Apolipoprotein-E Influences Aspects of Intellectual Ability in Type 1 Diabetes
1 Department of Diabetes, Royal Infirmary of Edinburgh, Edinburgh, Scotland, U.K.+, http://www.100md.com
2 Department of Psychology, University of Edinburgh, Edinburgh, Scotland, U.K.+, http://www.100md.com
3 Centre for Molecular Genetics, Exeter University, Exeter, England, U.K.+, http://www.100md.com
ABSTRACT+, http://www.100md.com
The {epsilon} 4 allele of the apolipoprotein-E (APOE) gene is associated with poor outcome following various cerebral insults. The relationship between APOE genotype and cognitive function in patients with type 1 diabetes is unknown. In a cross-sectional study of 96 people with type 1 diabetes, subjects were APOE genotyped, previous exposure to severe hypoglycemia was estimated by questionnaire, and cognition was assessed by neuropsychological testing. Cognitive abilities were compared using multivariate general linear modeling (multiple analysis of covariance, MANCOVA) in those with (n = 21) and without (n = 75) the APOE {epsilon} 4 allele. APOE {epsilon} 4 selectively influenced cognitive ability in a sex-specific manner (F = 2.3, P = 0.044, Eta2 = 0.15); women with APOE {epsilon} 4 performed less well on tests of current, nonverbal intellectual ability (Wechsler Adult Intelligence Scale-Revised performance test score, P = 0.001, Eta2 0.26) and frontal lobe and executive function (Borkowski verbal fluency, P = 0.016, Eta2 = 0.15). Previous exposure to severe hypoglycemia did not interact with APOE {epsilon} 4 to produce cognitive disadvantage. The APOE {epsilon} 4 genotype is associated with specific cognitive disadvantage in young women with type 1 diabetes. APOE {epsilon} 4 is unlikely to mediate susceptibility to hypoglycemia-induced cognitive disadvantage.
Permanent cognitive impairment is a rare consequence of insulin-induced hypoglycemia. In insulin-treated diabetes, severe hypoglycemia is common, with an annual prevalence of 30% in type 1 diabetes and a higher incidence in people with impaired awareness of hypoglycemia and strict glycemic control (1). Whether recurrent exposure to severe hypoglycemia promotes long-term cognitive sequelae is unresolved. Retrospective cross-sectional studies have indicated that some people with type 1 diabetes suffer a modest cognitive decrement (2), a finding not replicated by prospective observations for up to 10 years (3,4). The cross-sectional studies have reported individual differences in cognitive decrements in those exposed to severe hypoglycemia (2), suggesting that factors other than neuroglycopenia may influence the risk of developing subsequent cognitive impairment. Chronological age, diabetes duration, and coexistent microvascular and macrovascular complications have been proposed as potential mediators of susceptibility to hypoglycemia-induced cognitive impairment (2), whereas genetic susceptibility has not been examined.
Genetic factors influence cognitive aging, and polymorphism of the gene for apolipoprotein-E (APOE) is the most important genetic determinant of late-onset Alzheimer’s disease (5). The APOE gene has three common alleles ({epsilon} 2, {epsilon} 3, and {epsilon} 4) coding for three protein isoforms (designated E2, E3, and E4). Apolipoprotein-E (APOE) mediates central nervous system cholesterol transport in an isoform-specific manner (6). APOE activity is important in neuronal repair and maintenance, and the least active E4-isoform confers a survival disadvantage to injured neurons (6). APOE polymorphism influences cognitive ability in health and disease—apparently healthy middle-aged adults possessing the {epsilon} 4 allele have, on average, relatively low learning and memory ability (7); the {epsilon} 4 allele is associated with poorer cognitive and neurological outcome in head injury, demyelinating disease, intracerebral hemorrhage, and cardiopulmonary bypass surgery (8)..x?@^, http://www.100md.com
The aim of the present study was to examine whether possession of the APOE {epsilon} 4 allele was associated with cognitive disadvantage in people with type 1 diabetes, and secondly, to determine whether the magnitude of any difference in cognitive ability was modified by preceding exposure to recurrent severe hypoglycemia.
RESEARCH DESIGN AND METHODS+85w}pw, 百拇医药
A total of 96 people with type 1 diabetes were recruited and all completed the cross-sectional study protocol. Participants were selected from two preexisting cohorts (63 patients [9], 33 patients [10]), each of which had completed identical neuropsychological assessments. To minimize influences confounding neuropsychological performance, the following exclusion criteria were applied: hypertension (defined as blood pressure >140/90 mmHg), any previous central nervous system pathology, psychiatric disease, alcoholism or drug misuse, or multisystem disease known to affect the central nervous system.+85w}pw, 百拇医药
Assessment of neuropsychological function.+85w}pw, 百拇医药
The neuropsychological test battery was chosen to be sensitive to cognitive decrements across diverse cognitive abilities. Assessors blinded to the diabetes characteristics and APOE genotype of participants administered the neuropsychological tests in a fixed order. Incipient hypoglycemia, or hypoglycemia within the preceding 24 h, was excluded before neuropsychological assessment. Evidence of biochemical (blood glucose <3.5 mmol/l) or symptomatic hypoglycemia resulted in rescheduling of the neuropsychological session. The psychometric instruments used were as follows:
The Hospital Anxiety and Depression Scale (11) evaluated potential confounding effects of low mood and anxiety.1rs$\(, http://www.100md.com
The Wechsler Adult Intelligence Scale-Revised (WAIS-R) (12) uses performance subtests to measure current intellectual performance (fluid and nonverbal intelligence) and are sensitive to disruption by organic brain disease. Four performance subtests were utilized (picture completion, object assembly, block design, and digit symbol tests).1rs$\(, http://www.100md.com
The National Adult Reading Test (NART) (13) is relatively resistant to the effect of age and some types of organic brain disease. NART performance correlates more closely with premorbid IQ than demographic variables and was used to control for the confounding effects of prior intellectual ability (premorbid IQ, crystallized intelligence) in the present study.1rs$\(, http://www.100md.com
Inspection time (14) was used to assess visual perceptual speed, a component of information processing ability. Participants discriminated between the spatial position (left or right) of the longer of two briefly presented vertical lines. The stimuli were backward-masked, the presentation duration was varied, and the duration of time required to reliably distinguish the stimulus (85% correct) was termed the "inspection time."
Choice reaction time (15) was used to assess psychomotor speed and completed tests of information processing ability, and 1,2,4,8- and 8,4,2,1-choice reaction times were examined.m*@p1cd, http://www.100md.com
The Borkowski Verbal Fluency Test (controlled association) (16) is thought to assess frontal lobe and executive function. Participants have 60 s to state as many words as possible, beginning with letters of the alphabet specified by the assessor.m*@p1cd, http://www.100md.com
The Paced Auditory Serial Addition Task (17) was used to assess the ability to sustain attention and concentration. Participants listened to a number list, which they were required to add together according to a given rule. After practice, two consecutive 61-number trials were performed with 4 and 2 s between successive digits, respectively.m*@p1cd, http://www.100md.com
Assessment of severe hypoglycemia exposure.m*@p1cd, http://www.100md.com
Severe hypoglycemia was defined as an episode requiring external assistance to facilitate recovery (18), and exposure was assessed retrospectively using a validated and formatted hypoglycemia questionnaire (9). Participants were asked to discuss their history of severe hypoglycemia with family, partners, or friends before completing questionnaires to improve accuracy of estimates. The total number of lifetime episodes, frequency of episodes, and total numbers of hypoglycemic seizures, coma, and episodes requiring medical intervention were recorded.
Determination of APOE genotype.:]y/|6c, http://www.100md.com
DNA was extracted from venous blood from all subjects using standard methods. APOE genotyping was performed using a PCR-restriction fragment-length polymorphism assay as described by Wenham et al. (19).:]y/|6c, http://www.100md.com
Statistical analysis.:]y/|6c, http://www.100md.com
SPSS version 10.0 (SPSS, Chicago, IL) was used for statistical analysis. Demographic factors influencing neuropsychological performance (age, sex, and duration of diabetes), premorbid intellectual ability (NART), and the groupings of interest (severe hypoglycemia category, APOE genotype) were evaluated by multivariate general linear modeling (multiple analysis of covariance, MANCOVA). Severe hypoglycemia was dichotomized into two groups (group 1 = naïve to severe hypoglycemia; group 2 = previously exposed to severe hypoglycemia) based upon the total number of previous episodes. APOE genotype was categorized into two groups ({epsilon} 4-, {epsilon} 4+). MANCOVA was used to determine the significance (P) and magnitude (Eta2) of the variables’ effects on cognitive performance.
Subjects.:&o3, http://www.100md.com
The clinical characteristics of participants are shown in . Data on glycemic control have not been included as the laboratory reference ranges, and the methodology for estimating glycated hemoglobin changed across the two time frames during which data from participants were collated.:&o3, http://www.100md.com
fig.ommtted:&o3, http://www.100md.com
Characteristics of participants subdivided by the presence of the APOE {epsilon} 4 allele:&o3, http://www.100md.com
Subdivision of participants by APOE {epsilon} 4 produced two groups, {epsilon} 4+ (n = 21) and {epsilon} 4- (n = 75). The clinical characteristics are shown in . The subgroups had similar premorbid intellectual ability (NART) and similar exposure to severe hypoglycemia. Those possessing {epsilon} 4 were slightly older (P = 0.033, t test) and tended to have had diabetes of longer duration (P = 0.059, t test).:&o3, http://www.100md.com
RESULTS:&o3, http://www.100md.com
Severe hypoglycemia and neuropsychological performance.
The range of exposure to severe hypoglycemia was wide, from those with naïve to severe hypoglycemia (30%) to those who had experienced >10 episodes (29%) . No significant difference in cognitive ability was observed between those previously exposed to severe hypoglycemia and those naïve to severe hypoglycemia (estimated marginal mean differences for those with and without a history of severe hypoglycemia are shown in ).7, 百拇医药
fig.ommtted7, 百拇医药
Effect of severe hypoglycemia on cognitive ability and interaction with APOE7, 百拇医药
APOE {epsilon} 4 and neuropsychological performance.7, 百拇医药
The APOE {epsilon} 4 allele was associated with a disadvantage in current intellectual performance (WAIS-R performance test score, P = 0.037, Eta2 = 0.072) and a trend toward poorer frontal lobe and executive functions (Borkowski Verbal Fluency, P = 0.063, Eta2 = 0.057) after consideration of age, sex, duration of diabetes, preceding severe hypoglycemia, and premorbid intellectual ability . The relative disadvantage associated with APOE {epsilon} 4 appeared to be sex-specific (APOE x sex interaction: F = 2.28, P = 0.04, Eta2 = 0.15). Because of the sex specificity, MANCOVA thereafter was performed separately for men and women, using a similar model but excluding sex as a between-subjects factor. APOE genotype significantly influenced cognitive ability in women but not in men . Women with APOE {epsilon} 4 exhibited a significant cognitive disadvantage affecting current intellectual performance (WAIS-R performance test score, P = 0.001, Eta2 = 0.26) and frontal lobe and executive function (Borkowski Verbal Fluency, P = 0.016, Eta2 = 0.15). The difference in ability associated with possession of APOE {epsilon} 4 in women was moderate-to-large (Eta2).
fig.ommttedg, http://www.100md.com
Effect of APOE ({epsilon} 4- and {epsilon} 4+), age, and premorbid intellectual ability (NART) on cognitive performanceg, http://www.100md.com
fig.ommttedg, http://www.100md.com
APOE alleles, cognition, and sexg, http://www.100md.com
Apolipoprotein-E genotype and severe hypoglycemia.g, http://www.100md.com
There was no statistical evidence of a detrimental interaction between APOE genotype, previous exposure to severe hypoglycemia, and cognitive ability (APOE x severe hypoglycemia interaction: F = 0.66, P = 0.68, Eta2 = 0.05). The cognitive ability of subjects with the APOE 4 allele, subdivided into those exposed previously to severe hypoglycemia (n = 15) and those with naïve to severe hypoglycemia (n = 6), is shown in . No significant difference in cognitive ability was demonstrated between the subgroups, although the numbers of subjects in this analysis are too small to be confident of a nonsignificant difference .g, http://www.100md.com
DISCUSSION
The presence of the APOE {epsilon} 4 allele was associated with a significant disadvantage in current intellectual performance (WAIS-R performance test score) and in frontal lobe and executive functions (Borkowski Verbal Fluency) in women with type 1 diabetes. The deficits did not encompass all aspects of cognitive ability, were present only in women, and were evident at a younger age (39 years) than that which has been reported in people who do not have diabetes (7). Female susceptibility to APOE {epsilon} 4-associated cognitive disadvantage has been described for WAIS-R performance test ability in healthy elderly women (20), although the pathogenesis of the possible sex difference remains unclear. Age influences the effect of APOE {epsilon} 4 on cognitive ability; neuropsychological performance in healthy children (21) and healthy young adults (22) is not affected by the {epsilon} 4 allele, but middle-aged otherwise healthy adults (mean age 46 years) have been observed to have impaired learning and memory ability (7). The younger age (median age 39 years) at which {epsilon} 4-associated cognitive disadvantage was observed in adults with type 1 diabetes in the present study implies premature susceptibility compared with nondiabetic individuals.
Laboratory and clinical evidence supports the concept of {epsilon} 4-associated premature cognitive aging in diabetes. Elderly people with type 2 diabetes and the {epsilon} 4 allele exhibit greater cognitive decrement (23) and an accelerated cognitive decline (24) compared with age-matched {epsilon} 4 healthy control subjects; APOE from people with diabetes is irreversibly glycated and exhibits less in vitro bioactivity (25) when compared with nondiabetic control subjects. APOE bioactivity appears to have clinical relevance, as outcomes from a variety of cerebral pathologies are poorer in individuals possessing the least biologically active E4 isoform (8). As the present study did not include a healthy comparator group, the notion that APOE {epsilon} 4 is associated with premature cognitive aging in type 1 diabetes is speculative at present, whereas this has been demonstrated in type 2 diabetes (23,24).'0, 百拇医药
The present study did not support the hypothesis that polymorphism of the APOE gene may contribute to the susceptibility to hypoglycemia-induced cognitive decrement in people with type 1 diabetes. The number of subjects in each {epsilon} 4 subgroup (n = 15 with previous severe hypoglycemia vs. n = 6 hypoglycemia naïve) does not give sufficient power to allow definitive conclusions, and further, appropriately powered investigation is required to evaluate this hypothesis. Irrespective of the influence of APOE alleles, cognitive performance was unaffected by severe hypoglycemia per se, consistent with the conclusions of the Diabetes Control and Complications Trial (3) and the Stockholm Diabetes Intervention Study (4), in which many participants had type 1 diabetes of relatively short duration, but conflicting with retrospective cross-sectional studies (2) that examined older subjects with diabetes of long duration.
In conclusion, the data in this modestly powered study suggest that APOE {epsilon} 4 confers a cognitive disadvantage in young women who have type 1 diabetes. Further investigation is required to verify these findings and to determine whether the APOE {epsilon} 4 allele is associated with premature or accelerated cognitive aging in people who have type 1 diabetes, the diabetes-specific factors that may be mediating any such disadvantage, and the possible interaction with sex.6s, 百拇医药
ACKNOWLEDGMENTS6s, 百拇医药
S.C.F. was supported by funding from Eli Lilly & Company Ltd., and the study was supported by the Royal Infirmary of Edinburgh NHS Trust. J.C.E. received a Millhayes Scholarship from Exeter University. I.J.D. is the recipient of a Royal Society-Wolfson Research Merit Award.6s, 百拇医药
REFERENCES6s, 百拇医药
Tattersall RB: Frequency, causes and treatment of hypoglycaemia. In Hypoglycaemia in Clinical Diabetes. Frier BM, Fisher BM, Eds. Chichester, John Wiley & Sons Ltd.,1999 , p.55 –88
Perros P, Deary IJ: Long term effect of hypoglycaemia on cognitive function and the brain in diabetes. In Hypoglycaemia in Clinical Diabetes. Frier BM, Fisher BM, Eds. Chichester, John Wiley & Sons Ltd.,1999 , p.187 –210(z, 百拇医药
Diabetes Control and Complications Trial Research Group: Effects of intensive diabetes therapy on neuropsychological function in adults in the Diabetes Control and Complications Trial. Ann Intern Med124 :379 –388,1996(z, 百拇医药
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Corder EH, Saunders AM, Strittmatter WJ, Schmechel DE, Gaskell PC, Small GW, Roses AD, Haines JL, Pericak-Vance MA: Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer’s disease in late onset families. Science261 :921 –923,1993(z, 百拇医药
Maclullich AMJ, Seckl JR, Starr JM, Deary IJ: The biology of intelligence: from association to mechanism. Intelligence26 :63 –73,1998
Flory JD, Manuck SB, Ferrell RE, Ryan CM, Muldoon MF: Memory performance and the apolipoprotein E polymorphism in a community sample of middle-aged adults. Am J Med Genet96 :707 –711,2000l, 百拇医药
Smith JD: Apolipoprotein E4: an allele associated with many diseases. Ann Med32 :118 –127,2000l, 百拇医药
Deary IJ, Crawford JR, Hepburn DA, Langan SJ, Blackmore LM, Frier BM: Severe hypoglycemia and intelligence in adult patients with insulin-treated diabetes. Diabetes42 :341 –344,1993l, 百拇医药
Ferguson SC, Blane A, Perros P, McCrimmon RJ, Best JJK, Wardlaw J, Dreary IJ, Frier BM: Cognitive ability and brain structure in type 1 diabetes: relation to microangiopathy and preceding severe hypoglycemia. Diabetes52 :149 –156,2003l, 百拇医药
Zigmond AS, Snaith RP: The Hospital Anxiety and Depression Scale. Acta Psychiatr Scand67 :361 –370,1983l, 百拇医药
Wechsler D: Manual for the Wechsler Adult Intelligence Scale-Revised. New York, Psychological Corporation,1981l, 百拇医药
Nelson HE, Willison JR: National Adult Reading Test (NART) Test Manual. 2nd ed. Windsor, NFER-Nelson,1991
McCrimmon RJ, Deary IJ, Huntly BJH, MacLeod KJM, Frier BM: Visual information processing during controlled hypoglycaemia in humans. Brain119 :1277 –1287,199693@%h, 百拇医药
Jensen AR: Individual differences in the Hick paradigm. In Speed of Information Processing and Intelligence. Vernon PA, Ed. Norwood, NJ, Ablex,1987 , p.101 –17593@%h, 百拇医药
Borkowski JG, Benton AL: Word fluency and brain damage. Neuropsychologia5 :135 –140.,196793@%h, 百拇医药
Deary IJ, Langan SJ, Hepburn DA, Frier BM: Which abilities does the PASAT test? Pers Indiv Diff12 :983 –987,199193@%h, 百拇医药
The Diabetes Control and Complications Trial Research Group: Hypoglycemia in the Diabetes Control and Complications Trial. Diabetes46 :271 –286,199793@%h, 百拇医药
Wenham PR, Price WH, Blandell G: Apolipoprotein E genotyping by one-stage PCR. Lancet337 :1158 –1159,199193@%h, 百拇医药
Mortensen EL, Hogh P: A gender difference in the association between APOE genotype and age-related cognitive decline. Neurology57 :89 –95,200193@%h, 百拇医药
Turic D, Fisher PJ, Plomin R, Owen MJ: No association between apolipoprotein E polymorphisms and general cognitive ability in children. Neurosci Lett299 :97 –100,200193@%h, 百拇医药
Yu YW, Lin CH, Chen SP, Hong CJ, Tsai SJ: Intelligence and event-related potentials for young female human volunteer apolipoprotein E epsilon4 and non-epsilon4 carriers. Neurosci Lett294 :179 –181,200093@%h, 百拇医药
Kalmijn S, Feskens EJ, Launer LJ, Kromhout D: Cerebrovascular disease, the apolipoprotein e4 allele, and cognitive decline in a community-based study of elderly men. Stroke27 :2230 –2235,199693@%h, 百拇医药
Haan MN, Shemanski L, Jagust WJ, Manolio TA, Kuller L: The role of APOE epsilon4 in modulating effects of other risk factors for cognitive decline in elderly persons. JAMA282 :40 –46,199993@%h, 百拇医药
Shuvaev VV, Fujii J, Kawasaki Y, Itoh H, Hamaoka R, Barbier A, Ziegler O, Siest G, Taniguchi N: Glycation of apolipoprotein E impairs its binding to heparin: identification of the major glycation site. Biochim Biophys Acta1454 :296 –308,1999(Stewart C. Ferguson Ian J. Deary Julie C. Evans Sian Ellar Andrew T. Hattersley and Brian M. Frier)
2 Department of Psychology, University of Edinburgh, Edinburgh, Scotland, U.K.+, http://www.100md.com
3 Centre for Molecular Genetics, Exeter University, Exeter, England, U.K.+, http://www.100md.com
ABSTRACT+, http://www.100md.com
The {epsilon} 4 allele of the apolipoprotein-E (APOE) gene is associated with poor outcome following various cerebral insults. The relationship between APOE genotype and cognitive function in patients with type 1 diabetes is unknown. In a cross-sectional study of 96 people with type 1 diabetes, subjects were APOE genotyped, previous exposure to severe hypoglycemia was estimated by questionnaire, and cognition was assessed by neuropsychological testing. Cognitive abilities were compared using multivariate general linear modeling (multiple analysis of covariance, MANCOVA) in those with (n = 21) and without (n = 75) the APOE {epsilon} 4 allele. APOE {epsilon} 4 selectively influenced cognitive ability in a sex-specific manner (F = 2.3, P = 0.044, Eta2 = 0.15); women with APOE {epsilon} 4 performed less well on tests of current, nonverbal intellectual ability (Wechsler Adult Intelligence Scale-Revised performance test score, P = 0.001, Eta2 0.26) and frontal lobe and executive function (Borkowski verbal fluency, P = 0.016, Eta2 = 0.15). Previous exposure to severe hypoglycemia did not interact with APOE {epsilon} 4 to produce cognitive disadvantage. The APOE {epsilon} 4 genotype is associated with specific cognitive disadvantage in young women with type 1 diabetes. APOE {epsilon} 4 is unlikely to mediate susceptibility to hypoglycemia-induced cognitive disadvantage.
Permanent cognitive impairment is a rare consequence of insulin-induced hypoglycemia. In insulin-treated diabetes, severe hypoglycemia is common, with an annual prevalence of 30% in type 1 diabetes and a higher incidence in people with impaired awareness of hypoglycemia and strict glycemic control (1). Whether recurrent exposure to severe hypoglycemia promotes long-term cognitive sequelae is unresolved. Retrospective cross-sectional studies have indicated that some people with type 1 diabetes suffer a modest cognitive decrement (2), a finding not replicated by prospective observations for up to 10 years (3,4). The cross-sectional studies have reported individual differences in cognitive decrements in those exposed to severe hypoglycemia (2), suggesting that factors other than neuroglycopenia may influence the risk of developing subsequent cognitive impairment. Chronological age, diabetes duration, and coexistent microvascular and macrovascular complications have been proposed as potential mediators of susceptibility to hypoglycemia-induced cognitive impairment (2), whereas genetic susceptibility has not been examined.
Genetic factors influence cognitive aging, and polymorphism of the gene for apolipoprotein-E (APOE) is the most important genetic determinant of late-onset Alzheimer’s disease (5). The APOE gene has three common alleles ({epsilon} 2, {epsilon} 3, and {epsilon} 4) coding for three protein isoforms (designated E2, E3, and E4). Apolipoprotein-E (APOE) mediates central nervous system cholesterol transport in an isoform-specific manner (6). APOE activity is important in neuronal repair and maintenance, and the least active E4-isoform confers a survival disadvantage to injured neurons (6). APOE polymorphism influences cognitive ability in health and disease—apparently healthy middle-aged adults possessing the {epsilon} 4 allele have, on average, relatively low learning and memory ability (7); the {epsilon} 4 allele is associated with poorer cognitive and neurological outcome in head injury, demyelinating disease, intracerebral hemorrhage, and cardiopulmonary bypass surgery (8)..x?@^, http://www.100md.com
The aim of the present study was to examine whether possession of the APOE {epsilon} 4 allele was associated with cognitive disadvantage in people with type 1 diabetes, and secondly, to determine whether the magnitude of any difference in cognitive ability was modified by preceding exposure to recurrent severe hypoglycemia.
RESEARCH DESIGN AND METHODS+85w}pw, 百拇医药
A total of 96 people with type 1 diabetes were recruited and all completed the cross-sectional study protocol. Participants were selected from two preexisting cohorts (63 patients [9], 33 patients [10]), each of which had completed identical neuropsychological assessments. To minimize influences confounding neuropsychological performance, the following exclusion criteria were applied: hypertension (defined as blood pressure >140/90 mmHg), any previous central nervous system pathology, psychiatric disease, alcoholism or drug misuse, or multisystem disease known to affect the central nervous system.+85w}pw, 百拇医药
Assessment of neuropsychological function.+85w}pw, 百拇医药
The neuropsychological test battery was chosen to be sensitive to cognitive decrements across diverse cognitive abilities. Assessors blinded to the diabetes characteristics and APOE genotype of participants administered the neuropsychological tests in a fixed order. Incipient hypoglycemia, or hypoglycemia within the preceding 24 h, was excluded before neuropsychological assessment. Evidence of biochemical (blood glucose <3.5 mmol/l) or symptomatic hypoglycemia resulted in rescheduling of the neuropsychological session. The psychometric instruments used were as follows:
The Hospital Anxiety and Depression Scale (11) evaluated potential confounding effects of low mood and anxiety.1rs$\(, http://www.100md.com
The Wechsler Adult Intelligence Scale-Revised (WAIS-R) (12) uses performance subtests to measure current intellectual performance (fluid and nonverbal intelligence) and are sensitive to disruption by organic brain disease. Four performance subtests were utilized (picture completion, object assembly, block design, and digit symbol tests).1rs$\(, http://www.100md.com
The National Adult Reading Test (NART) (13) is relatively resistant to the effect of age and some types of organic brain disease. NART performance correlates more closely with premorbid IQ than demographic variables and was used to control for the confounding effects of prior intellectual ability (premorbid IQ, crystallized intelligence) in the present study.1rs$\(, http://www.100md.com
Inspection time (14) was used to assess visual perceptual speed, a component of information processing ability. Participants discriminated between the spatial position (left or right) of the longer of two briefly presented vertical lines. The stimuli were backward-masked, the presentation duration was varied, and the duration of time required to reliably distinguish the stimulus (85% correct) was termed the "inspection time."
Choice reaction time (15) was used to assess psychomotor speed and completed tests of information processing ability, and 1,2,4,8- and 8,4,2,1-choice reaction times were examined.m*@p1cd, http://www.100md.com
The Borkowski Verbal Fluency Test (controlled association) (16) is thought to assess frontal lobe and executive function. Participants have 60 s to state as many words as possible, beginning with letters of the alphabet specified by the assessor.m*@p1cd, http://www.100md.com
The Paced Auditory Serial Addition Task (17) was used to assess the ability to sustain attention and concentration. Participants listened to a number list, which they were required to add together according to a given rule. After practice, two consecutive 61-number trials were performed with 4 and 2 s between successive digits, respectively.m*@p1cd, http://www.100md.com
Assessment of severe hypoglycemia exposure.m*@p1cd, http://www.100md.com
Severe hypoglycemia was defined as an episode requiring external assistance to facilitate recovery (18), and exposure was assessed retrospectively using a validated and formatted hypoglycemia questionnaire (9). Participants were asked to discuss their history of severe hypoglycemia with family, partners, or friends before completing questionnaires to improve accuracy of estimates. The total number of lifetime episodes, frequency of episodes, and total numbers of hypoglycemic seizures, coma, and episodes requiring medical intervention were recorded.
Determination of APOE genotype.:]y/|6c, http://www.100md.com
DNA was extracted from venous blood from all subjects using standard methods. APOE genotyping was performed using a PCR-restriction fragment-length polymorphism assay as described by Wenham et al. (19).:]y/|6c, http://www.100md.com
Statistical analysis.:]y/|6c, http://www.100md.com
SPSS version 10.0 (SPSS, Chicago, IL) was used for statistical analysis. Demographic factors influencing neuropsychological performance (age, sex, and duration of diabetes), premorbid intellectual ability (NART), and the groupings of interest (severe hypoglycemia category, APOE genotype) were evaluated by multivariate general linear modeling (multiple analysis of covariance, MANCOVA). Severe hypoglycemia was dichotomized into two groups (group 1 = naïve to severe hypoglycemia; group 2 = previously exposed to severe hypoglycemia) based upon the total number of previous episodes. APOE genotype was categorized into two groups ({epsilon} 4-, {epsilon} 4+). MANCOVA was used to determine the significance (P) and magnitude (Eta2) of the variables’ effects on cognitive performance.
Subjects.:&o3, http://www.100md.com
The clinical characteristics of participants are shown in . Data on glycemic control have not been included as the laboratory reference ranges, and the methodology for estimating glycated hemoglobin changed across the two time frames during which data from participants were collated.:&o3, http://www.100md.com
fig.ommtted:&o3, http://www.100md.com
Characteristics of participants subdivided by the presence of the APOE {epsilon} 4 allele:&o3, http://www.100md.com
Subdivision of participants by APOE {epsilon} 4 produced two groups, {epsilon} 4+ (n = 21) and {epsilon} 4- (n = 75). The clinical characteristics are shown in . The subgroups had similar premorbid intellectual ability (NART) and similar exposure to severe hypoglycemia. Those possessing {epsilon} 4 were slightly older (P = 0.033, t test) and tended to have had diabetes of longer duration (P = 0.059, t test).:&o3, http://www.100md.com
RESULTS:&o3, http://www.100md.com
Severe hypoglycemia and neuropsychological performance.
The range of exposure to severe hypoglycemia was wide, from those with naïve to severe hypoglycemia (30%) to those who had experienced >10 episodes (29%) . No significant difference in cognitive ability was observed between those previously exposed to severe hypoglycemia and those naïve to severe hypoglycemia (estimated marginal mean differences for those with and without a history of severe hypoglycemia are shown in ).7, 百拇医药
fig.ommtted7, 百拇医药
Effect of severe hypoglycemia on cognitive ability and interaction with APOE7, 百拇医药
APOE {epsilon} 4 and neuropsychological performance.7, 百拇医药
The APOE {epsilon} 4 allele was associated with a disadvantage in current intellectual performance (WAIS-R performance test score, P = 0.037, Eta2 = 0.072) and a trend toward poorer frontal lobe and executive functions (Borkowski Verbal Fluency, P = 0.063, Eta2 = 0.057) after consideration of age, sex, duration of diabetes, preceding severe hypoglycemia, and premorbid intellectual ability . The relative disadvantage associated with APOE {epsilon} 4 appeared to be sex-specific (APOE x sex interaction: F = 2.28, P = 0.04, Eta2 = 0.15). Because of the sex specificity, MANCOVA thereafter was performed separately for men and women, using a similar model but excluding sex as a between-subjects factor. APOE genotype significantly influenced cognitive ability in women but not in men . Women with APOE {epsilon} 4 exhibited a significant cognitive disadvantage affecting current intellectual performance (WAIS-R performance test score, P = 0.001, Eta2 = 0.26) and frontal lobe and executive function (Borkowski Verbal Fluency, P = 0.016, Eta2 = 0.15). The difference in ability associated with possession of APOE {epsilon} 4 in women was moderate-to-large (Eta2).
fig.ommttedg, http://www.100md.com
Effect of APOE ({epsilon} 4- and {epsilon} 4+), age, and premorbid intellectual ability (NART) on cognitive performanceg, http://www.100md.com
fig.ommttedg, http://www.100md.com
APOE alleles, cognition, and sexg, http://www.100md.com
Apolipoprotein-E genotype and severe hypoglycemia.g, http://www.100md.com
There was no statistical evidence of a detrimental interaction between APOE genotype, previous exposure to severe hypoglycemia, and cognitive ability (APOE x severe hypoglycemia interaction: F = 0.66, P = 0.68, Eta2 = 0.05). The cognitive ability of subjects with the APOE 4 allele, subdivided into those exposed previously to severe hypoglycemia (n = 15) and those with naïve to severe hypoglycemia (n = 6), is shown in . No significant difference in cognitive ability was demonstrated between the subgroups, although the numbers of subjects in this analysis are too small to be confident of a nonsignificant difference .g, http://www.100md.com
DISCUSSION
The presence of the APOE {epsilon} 4 allele was associated with a significant disadvantage in current intellectual performance (WAIS-R performance test score) and in frontal lobe and executive functions (Borkowski Verbal Fluency) in women with type 1 diabetes. The deficits did not encompass all aspects of cognitive ability, were present only in women, and were evident at a younger age (39 years) than that which has been reported in people who do not have diabetes (7). Female susceptibility to APOE {epsilon} 4-associated cognitive disadvantage has been described for WAIS-R performance test ability in healthy elderly women (20), although the pathogenesis of the possible sex difference remains unclear. Age influences the effect of APOE {epsilon} 4 on cognitive ability; neuropsychological performance in healthy children (21) and healthy young adults (22) is not affected by the {epsilon} 4 allele, but middle-aged otherwise healthy adults (mean age 46 years) have been observed to have impaired learning and memory ability (7). The younger age (median age 39 years) at which {epsilon} 4-associated cognitive disadvantage was observed in adults with type 1 diabetes in the present study implies premature susceptibility compared with nondiabetic individuals.
Laboratory and clinical evidence supports the concept of {epsilon} 4-associated premature cognitive aging in diabetes. Elderly people with type 2 diabetes and the {epsilon} 4 allele exhibit greater cognitive decrement (23) and an accelerated cognitive decline (24) compared with age-matched {epsilon} 4 healthy control subjects; APOE from people with diabetes is irreversibly glycated and exhibits less in vitro bioactivity (25) when compared with nondiabetic control subjects. APOE bioactivity appears to have clinical relevance, as outcomes from a variety of cerebral pathologies are poorer in individuals possessing the least biologically active E4 isoform (8). As the present study did not include a healthy comparator group, the notion that APOE {epsilon} 4 is associated with premature cognitive aging in type 1 diabetes is speculative at present, whereas this has been demonstrated in type 2 diabetes (23,24).'0, 百拇医药
The present study did not support the hypothesis that polymorphism of the APOE gene may contribute to the susceptibility to hypoglycemia-induced cognitive decrement in people with type 1 diabetes. The number of subjects in each {epsilon} 4 subgroup (n = 15 with previous severe hypoglycemia vs. n = 6 hypoglycemia naïve) does not give sufficient power to allow definitive conclusions, and further, appropriately powered investigation is required to evaluate this hypothesis. Irrespective of the influence of APOE alleles, cognitive performance was unaffected by severe hypoglycemia per se, consistent with the conclusions of the Diabetes Control and Complications Trial (3) and the Stockholm Diabetes Intervention Study (4), in which many participants had type 1 diabetes of relatively short duration, but conflicting with retrospective cross-sectional studies (2) that examined older subjects with diabetes of long duration.
In conclusion, the data in this modestly powered study suggest that APOE {epsilon} 4 confers a cognitive disadvantage in young women who have type 1 diabetes. Further investigation is required to verify these findings and to determine whether the APOE {epsilon} 4 allele is associated with premature or accelerated cognitive aging in people who have type 1 diabetes, the diabetes-specific factors that may be mediating any such disadvantage, and the possible interaction with sex.6s, 百拇医药
ACKNOWLEDGMENTS6s, 百拇医药
S.C.F. was supported by funding from Eli Lilly & Company Ltd., and the study was supported by the Royal Infirmary of Edinburgh NHS Trust. J.C.E. received a Millhayes Scholarship from Exeter University. I.J.D. is the recipient of a Royal Society-Wolfson Research Merit Award.6s, 百拇医药
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