Positive Selection of CAG Repeats of the ATXN2 Gene in Chinese Ethnic Groups

The ataxin-2 （ATXN2） gene is located on human chromo-some 12q24.1. In normal individuals, the coding region in exon 1 of this gene has fewer than 31 CAG repeats （Yu et al., 2005： Laffita-Mesa et al., 2012）. However, an abnormal expansion of CAG trinucleotide repeats results in the aggre-gation of polyglutamine （polyQ）, which causes spinocer-ebellar ataxia type 2 （SCA2） （Pulst et al., 1996）. The expanded alleles have more than 32 repeats in the affected individuals, and generally there is an inverse correlation between CAG repeat length and age of onset （Pulst et al., 1996）. SCA2 is an autosomal dominant inheritance neurodegenerative disease, whose major clinical feature is progressive cerebellar ataxia. Atrophies of the brainstem and frontal lobe have been frequently detected by magnetic resonance imaging （MRI） （Yamamoto-Watanabe et al., 2010）. This disease has the strong effect on sensory and motor control.

Androgen insensitivity syndrome： do trinucleotide repeats in androgen receptor gene have any role？

Aim： To investigate the role of CAG and GGN repeats as genetic background affecting androgen insensitivity syndrome （AIS） phenotype. Methods： We analyzed lengths of androgen receptor （AR）-CAG and GGN repeats in 69 AIS cases, along with 136 unrelated normal male individuals. The lengths of repeats were analyzed using polymerase chain reaction （PCR） amplification followed by allelic genotyping to determine allele length. Results： Our study revealed significantly shorter mean lengths of CAG repeats in patients （mean 18.25 repeats, range 14-26 repeats） in comparison to the controls （mean 22.57 repeats, range 12-39 repeats） （two-tailed P 〈 0.0001）. GGN repeats, however, did not differ significantly between patients （mean 21.48 repeats） and controls （mean 21.21 repeats） （two- tailed P = 0.474）. Among patients＇ groups, the mean number of CAG repeats in partial androgen insensitivity cases （mean 15.83 repeats） was significantly less than in complete androgen insensitivity cases （mean 19.46 repeats） （two- tailed P 〈 0.0001）. Conclusion： The findings suggest that shorter lengths of repeats in the AR gene might act as low penetrance genetic background in varying manifestation of androgen insensitivity.

Relationships among androgen receptor CAG repeat polymorphism, sex hormones and penile length in Han adult men from China： a cross-sectional study

This study aimed to investigate the correlations among androgen receptor （AR） CAG repeat polymorphism, sex hormones and penile length in healthy Chinese young adult men. Two hundred and fifty-three healthy men （aged 22.8 ± 3.1years） were enrolled. The individuals were grouped as CAG short （CAGs） if they harbored repeat length of 〈20 or as CAG long （CAGL） if their CAG repeat length was 〉20. Body height/weight, penile length and other parameters were examined and recorded by the specified physicians; CAG repeat polymorphism was determined by the polymerase chain reaction （PCR） method; and the serum levels of the sex hormones were detected by radioimmunoassay. Student＇s t-test or linear regression analysis was used to assess the associations among AR CAG repeat polymorphism, sex hormones and penile length. This investigation showed that the serum total testosterone （T） level was positively associated with the AR CAG repeat length （P = 0.01）; whereas, no significant correlation of T or AR CAG repeat polymorphism with the penile length was found （P = 0.593）. Interestingly, an inverse association was observed between serum prolactin （PRL） levels and penile length by linear regression analyses （β = -0.024, P = 0.039, 95% confidence interval （CI）： -0.047, 0）. Collectively, this study provides the first evidence that serum PRL, but not T or AR CAG repeat polymorphism, is correlated with penile length in the Han adult population from northwestern China.

Bulbocavernosus muscle area measurement： a novel method to assess androgenic activity

Serum testosterone does not correlate with androgen tissue activity, and it is critical to optimize tools to evaluate such activity in males. Ultrasound measurement of bulbocavernosus muscle （BCM） was used to assess the relationship between the number of CAG repeats （CAGn） in the androgen receptor （AR） and the BCM size; the changes in the number of CAGn over age were also evaluated. Transperineal ultrasound measurement of the BCM was also performed. AR CAGn were determined by high performance liquid chromatography, and morning hormone levels were determined using immunoassays. Forty-eight men had CAG repeat analysis. Twenty-five were 〈30 years of age, mean 23.7 years （s.d, = 3.24） and 23 were 〉45 years of age, mean 53years （s.d. = 5.58）. The median CAGn was 21 （13-29）. BCM area was greater when the number of CAGn were 〈18 as compared to the number of CAGn 〉24 （P= 0.04）. There was a linear correlation between the number of CAGn and the BCM area R^2= 16% （P= 0.01）. In the 45 to 65-years-old group, a much stronger negative correlation （R^2 = 29%, P= 0.01） was noticed. In the 19 to 29-years-old group, no such correlation was found （R2 = 4%, P = 0.36）. In older men, the number of CAGn increased with age （R^2 = 32%, P= 0.01）. The number of CAGn in the AR correlates with the area of the BCM. Ultrasound assessment of the BCM is an effective surrogate to evaluate end-organ activity of androgens. The number of CAGn may increase with age.

Predictors for partial suppression of spermatogenesis of hormonal male contraception

Aim： To analyze factors influencing the efficacy of hormonal suppression of spermatogenesis for male contraception. Methods： A nested case-control study was conducted, involving 43 subjects, who did not achieve azoospermia or severe oligozoospermia when given monthly injections of 500 mg testosterone undecanoate （TU）, defined as partial suppressors compared with 855 subjects who had suppressed spermatogenesis （complete suppressors）. Sperm density, serum testosterone, luteinizing hormone （LH） and follicle stimulating hormone （FSH） concentrations at the baseline and the suppression phase were compared between partial and complete suppressors. Polymorphisms of androgen receptor （AR） and three single nucleotide variants and their haplotypes of FSH receptor （FSHR） genes determined by polymerase chain reaction （PCR） and DNA sequencing technique were compared between 29 partial and 34 complete suppressors. Results： Baseline serum LH level was higher and serum LH as well as FSH level during the suppression phase was less suppressed in partial suppressors. Additionally, in a logistic regression analysis larger testis volume, higher serum FSH concentrations alone, or interaction of serum LH, FSH, testosterone and sperm concentrations were associated with degree of suppression. The distribution of polymorphisms of AR or FSH receptor genes did not differ between partial and complete suppressors. In cases with incomplete FSH suppression （FSH 〉 0.2 IU/L）, the chances of reaching azoospermia were 1.5 times higher in the subjects with more than 22 CAG triplet repeats. Conclusion： Partial suppression of spermatogenesis induced by 500 mg TU monthly injections is weakly influenced by hormonal and clinical features but not polymorphism in AR and FSHR genes.

Phenotypic heterogeneity of mutations in androgen receptor gene

Androgen receptor （AR） gene has been extensively studied in diverse clinical conditions. In addition to the point mutations, trinucleotide repeat （CAG and GGN） length polymorphisms have been an additional subject of interest and controversy among geneticists. The polymorphic variations in triplet repeats have been associated with a number of disorders, but at the same time contradictory findings have also been reported. Further, studies on the same disorder in different populations have generated different results. Therefore, combined analysis or review of the published studies has been of much value to extract information on the significance of variations in the gene in various clinical conditions. AR genetics has been reviewed extensively but until now review articles have focused on individual clinical categories such as androgen insensitivity, male infertility, prostate cancer, and so on. We have made the first effort to review most the aspects of AR genetics. The impact of androgens in various disorders and polymorphic variations in the AR gene is the main focus of this review. Additionally, the correlations observed in various studies have been discussed in the light of in vitro evidences available for the effect of AR gene variations on the action of androgens.

Examination of Huntington's disease in a Chinese family

We report brain imaging and genetic diagnosis in a family from Wuhan, China, with a history of Huntington＇s disease. Among 17 family members across three generations, four patients （Ⅱ2, Ⅱ6, Ⅲ5, and Ⅲ9） show typical Huntington＇s disease, involuntary dance-like movements. Magnetic resonance imaging found lateral ventricular atrophy in three members （Ⅱ2, Ⅱ6, and Ⅲ5）. Moreover, genetic analysis identified abnormally amplified CAG sequence repeats （〉 40） in two members （Ⅲ5 and Ⅲ9）. Among borderline cases, with clinical symptoms and brain imaging features of Huntington＇s disease, two cases were identified （Ⅱ2 and Ⅱ6）, but shown by mutation analysis for CAG expansions in the important transcript 15 gene, to be non-Huntington＇s disease. Our findings suggest that clinical diagnosis of Huntington＇s disease requires a combination of clinical symptoms, radiological changes, and genetic diagnosis.

Androgen receptor gene CAG and GGN repeat lengths as predictors of recovery of spermatogenesis following testicular germ cell cancer treatment

Spermatogenesis is an androgen-regulated process that depends on the action of androgen receptor （AR）. Sperm production may be affected in men treated for testicular cancer （TC）, and it is important to identify the factors influencing the timing of spermatogenesis recovery following cancer treatment. It is known that the CAG and GGN repeat numbers affect the activity of the AR; therefore, the aim of this study is to investigate if the CAG and GGN polymorphisms in the AR gene predict recovery of sperm production after TC treatment. TC patients （n = 130） delivered ejaculates at the following time points： postorchiectomy and at 6, 12, 24, 36, and 60 months posttherapy （TO, T6, T12, T24, T36, and T60）. The CAG lengths were categorized into three groups, 〈22 CAG, 22-23 CAG, and 〉23 CAG, and the GGN tracts were also categorized into three groups, 〈23 GGN, 23 GGN, and 〉23 GGN. At T12, men with 22-23 CAG presented with a statistically significantly （P = 0.045） lower sperm concentration than those with other CAG numbers （8.4 × 10^6 ml^-1 vs 16 × 10^6 ml^-1; 95% CI： 1.01-2.65）. This association was robust to omitting adjustment for treatment type and sperm concentration at TO （P= 0.021; 3.7× 10^6 ml^-1 vs 10 × 10^6 ml^-1; 95% CI： 1.13-4.90）. The same trends were observed for total sperm number. The least active AR variant seems to be associated with a more rapid recovery of spermatogenesis. This finding adds to our understanding of the biology of postcancer therapy recovery of fertility in males and has clinical implications.

Integrated analysis on transcriptome and behaviors defines HTT repeat-dependent network modules in Huntington's disease

Huntington's disease(HD)is caused by a CAG repeat expansion in the huntingtin(HTT)gene.Knock-in mice carrying a CAG repeat-expanded Htt will develop HD phenotypes.Previous studies suggested dysregulated molecular networks in a CAG length genotype-and the age-dependent manner in brain tissues from knock-in mice carrying expanded Htt CAG repeats.Furthermore,a large-scale phenome analysis defined a behavioral signature for HD genotype in knock-in mice carrying expanded Htt CAG repeats.However,an integrated analysis correlating phenotype features with genotypes(CAG repeat expansions)was not conducted previously.In this study,we revealed the landscape of the behavioral features and gene expression correlations based on 445 mRNA samples and 445 microRNA samples,together with behavioral features(396 PhenoCube behaviors and 111 NeuroCube behaviors)in Htt CAG-knock-in mice.We identified 37 behavioral features that were significantly associated with CAG repeat length including the number of steps and hind limb stand duration.The behavioral features were associated with several gene coexpression groups involved in neuronal dysfunctions,which were also supported by the single-cell RNA sequencing data in the striatum and the spatial gene expression in the brain.We also identified 15 chemicals with significant responses for genes with enriched behavioral features,most of them are agonist or antagonist for dopamine receptors and serotonin receptors used for neurology/psychiatry.Our study provides further evidence that abnormal neuronal signal transduction in the striatum plays an important role in causing HD-related phenotypic behaviors and provided rich information for the further pharmacotherapeutic intervention possibility for HD.