Allelic Distribution of Genes for Apolipoprotein E and MTHFR in Patients with Alzheimer's Disease and Their Epistatic Interaction.

BACKGROUND: Genetic risk factors play an important role in the pathogenesis of Alzheimer's disease (AD). However, the gene-gene interaction (epistasis) between specific allelic variants is only partially understood. OBJECTIVE: In our study, we examined the presence of the ɛ4 allele of apolipoprotein E (APOE) and the presence of C677T and A1298C (rs1801133 and rs1801131) polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene in patients with AD and controls. We also evaluated the epistatic interaction between MTHFR and the APOE variants. METHODS: A total of 564 patients with AD and 534 cognitively unimpaired age-matched controls were involved in the study. RESULTS: The presence of the ɛ4 allele of APOE increases the risk of developing AD in a dose-dependent manner (OR 32.7: homozygotes, 15.6: homozygotes + heterozygotes, 14.3: heterozygotes). The combination of genotypes also increases the risk of developing AD in a dose-dependent manner: OR 18.3 (APOE 4/X and 4/4 + CT rs1801133), OR 19.4 (APOE 4/X and 4/4 + CT rs1801133 + AC rs1801131), OR 22.4 (APOE 4/X and 4/4 + TT rs1801133), and OR 21.2 (APOE 4/X and 4/4 + CC rs1801131). Homozygotes for variant alleles of MTHFR as well as patients with AD had significantly higher levels of homocysteine than homozygotes for standard alleles or controls. CONCLUSION: Homozygotes for APOE4 and carriers of APOE4 with TT genotype of rs1801133 were found to be at the highest risk of developing AD. These findings suggest that the epistatic interaction of specific gene variants can have a significant effect on the development of AD.

Differing clinical presentations of two unrelated cases of X-linked adrenoleukodystrophy with identical mutation Y296C in the ABCD1 gene.

OBJECTIVES: X-linked adrenoleukodystrophy is a genetically determined disorder that causes varying degrees of malfunction of the adrenal cortex and central nervous system. Our aim was to investigate the occurrence of known, or new, mutations in the ABCD1 gene in two unrelated patients with clinical suspicion of the adrenoleukodystrophy. METHODS: Two unrelated patients - the first with behavioral changes, the second with progressive cognitive deficit - underwent a clinical and genetic examination in order to establish a diagnosis and discover a possible mutation. RESULTS: In the first patient, a 47 year old man, the clinical examination showed dementia of the frontal type and spastic quadriparesis. The patient also suffered from adrenal insufficiency for 6 years. An MRI showed confluent hyperintensive lesions in FLAIR images in the frontal lobe of both hemispheres. The second patient, a 16 year old boy, suffered also from Addison's disease since the age of 9, and developed cognitive deficit in the course of one year. The MRI showed posterior atrophy and hyperintensive lesions in parietal and occipital lobes in T2WI. In both cases, genetic analyses showed a missense mutation at the codon 887 (A>G) in exon 1 of the ABCD1 gene, predicting the substitution Y296C in the ALD protein. CONCLUSION: We detected the same mutation of the ABCD1 gene in two unrelated patients with ALD. In the first case there was frontal lobe involvement, in the second case parieto-occipital involvement. Both pathologic involvement and clinical presentation differed in two cases of the same mutation.