CAG repeat contraction in the androgen receptor gene in three brothers with mental retardation

Repeat variations in polyglutamine disease-associated genes and cognitive function in old age

Although the heritability of cognitive function in old age is substantial, genome-wide association studies have had limited success in elucidating its genetic basis, leaving a considerable amount of "missing heritability." Aside from single nucleotide polymorphisms, genome-wide association studies are unable to assess other large sources of genetic variation, such as tandem repeat polymorphisms. Therefore, here, we studied the association of cytosine-adenine-guanine (CAG) repeat variations in polyglutamine disease-associated genes (PDAGs) with cognitive function in older adults. In a large cohort consisting of 5786 participants, we found that the CAG repeat number in 3 PDAGs (TBP, HTT, and AR) were significantly associated with the decline in cognitive function, which together accounted for 0.49% of the variation. Furthermore, in an magnetic resonance imaging substudy, we found that CAG repeat polymorphisms in 4 PDAGs (ATXN2, CACNA1A, ATXN7, and AR) were associated with different imaging characteristics, including brain stem, putamen, globus pallidus, thalamus, and amygdala volumes. Our findings indicate that tandem repeat polymorphisms are associated with cognitive function in older adults and highlight the importance of PDAGs in elucidating its missing heritability.

Possible association between the androgen receptor gene and autism spectrum disorder

Autism is a highly heritable disorder but the specific genes involved remain largely unknown. The higher prevalence of autism in men than in women, in conjunction with a number of other observations, has led to the suggestion that prenatal brain exposure to androgens may be of importance for the development of this condition. Prompted by this hypothesis, we investigated the potential influence of variation in the androgen receptor (AR) gene on the susceptibility for autism. To this end, 267 subjects with autism spectrum disorder and 617 controls were genotyped for three polymorphisms in exon 1 of the AR gene: the CAG repeat, the GGN repeat and the rs6152 SNP. In addition, parents and affected siblings were genotyped for 118 and 32 of the cases, respectively. Case-control comparisons revealed higher prevalence of short CAG alleles as well as of the A allele of the rs6152 SNP in female cases than in controls, but revealed no significant differences with respect to the GGN repeat. Analysis of the 118 families using transmission disequilibrium test, on the other hand, suggested an association with the GGN polymorphism, the rare 20-repeat allele being undertransmitted to male cases and the 23-repeat allele being overtransmitted to female cases. Sequencing of the AR gene in 46 patients revealed no mutations or rare variants. The results lend some support for an influence of the studied polymorphisms on the susceptibility for autism, but argue against the possibility that mutations in the AR gene are common in subjects with this condition.

Clinical study and haplotype analysis in two brothers with Partington syndrome

Partington et al. [1988] described a three-generation family (MRXS1, MIM *309510, PRTS) with a syndromic form of X-linked mental retardation (XLMR). The clinical features in 10 affected males included mild to moderate MR, dystonic movements of the hands, and dysarthria. After refinement, the PRTS locus was mapped to marker DXS989 (with maximum LOD score of 3.1) with flanking markers DXS365 and DXS28. Since then, no other patients with a similar phenotype have been described. We present a detailed description of the neurological symptoms and the disease history of two brothers with the clinical features of PRTS. Psychomotor development was delayed in both, and neurological features included mild to moderate mental retardation, dysarthria, facial muscle weakness, severe dysdiadochokinesis, slow dystonic movements, and mild spasticity of the hands, without ataxia or spasticity of the legs. The symptoms were nonprogressive and extrapyramidal, and without cerebellar involvement. In general, behavior of the two brothers was friendly and quiet, although the elder brother had periods of depressed mood and outbursts of anger. Karyotypes and subsequent investigation of the subtelomeres as well as DNA analysis of the FMR1 gene, the androgen receptor gene, and the DM locus did not reveal a genetic abnormality. Haplotype analysis showed that the affected brothers share the PRTS region at Xp22.1. Mutation screening of the PDH-E1alpha gene did not reveal a pathogenic mutation.