Anogenital distance as a marker of androgen exposure in humans.

Abnormal foetal testis development has been proposed to underlie common disorders of the male reproductive system such as cryptorchidism, hypospadias, reduced semen quality and testicular germ cell tumour, which are regarded as components of a 'testicular dysgenesis syndrome'. The increasing trends and geographical variation in their incidence have been suggested to result from in utero exposure to environmental chemicals acting as endocrine disruptors. In rodents, the anogenital distance (AGD), measured from the anus to the base of genital tubercle, is a sensitive biomarker of androgen exposure during a critical embryonic window of testis development. In humans, several epidemiological studies have shown alterations in AGD associated with prenatal exposure to several chemicals with potential endocrine disrupting activity. However, the link between AGD and androgen exposure in humans is not well-defined. This review focuses on the current evidence for such a relationship. As in rodents, a clear gender difference is detected during foetal development of the AGD in humans which is maintained thereafter. Reduced AGD in association with clinically relevant outcomes of potential environmental exposures, such as cryptorchidism or hypospadias, is in keeping with AGD as a marker of foetal testicular function. Furthermore, AGD may reflect variations in prenatal androgen exposure in healthy children as shorter AGD at birth is associated with reduced masculine play behaviour in preschool boys. Several studies provide evidence linking shorter AGD with lower fertility, semen quality and testosterone levels in selected groups of adults attending andrology clinics. Overall, the observational data in humans are consistent with experimental studies in animals and support the use of AGD as a biomarker of foetal androgen exposure. Future studies evaluating AGD in relation to reproductive hormones in both infants and adults, and to gene polymorphisms, will help to further delineate the effect of prenatal and postnatal androgen exposures on AGD.The CBGS studies referred to in this review were supported by a European Union Framework V programme, the World Cancer Research Fund International, the Medical Research Council (UK), the Newlife Foundation, the Mothercare Foundation, the Evelyn Trust and the NIHR Cambridge Biomedical Research Centre.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/andr.1215

Trinucleotide (CAG) repeat polymorphism of the androgen receptor gene in human disease

Ph.DDOCTOR OF PHILOSOPH

Genetic analysis of male infertility

Approximately one in twenty men has impaired spermatogenesis due to mutation of genes involved in the establishment or maintenance of fertility. Our understanding of male infertility is complicated by the variable phenotypes produced by similar genetic changes, largely due to the practise of screening a single fertility gene in isolation. This thesis aimed to increase our understanding of the role of synergistic mutations in relation to differences in semen quality. Each sample was analysed for mutation in: CAG trinucleotide repeat variation in the X-linked androgen receptor (AR) gene, micro deletion within the three Y chromosome azoospermic factor (AZF) regions, and CAG trinucleotide repeat variation and exonuclease domain mutation in the nuclear polymerase gamma (POLγ gene. These genes have been associated with reduced semen quality in past research. Each gene region was amplified by polymerase chain reaction (PCR), followed by sequencing. Suspected AZF micro-deletions were confirmed by Southern blot hybridisation. Associations with semen quality were evaluated using either a t-test or Gtest for independence at α=0.05. Yq AZF micro-deletions were observed in 6.6% (14/211) of men with poor semen quality but not in normozoospermic samples (0/104); P<0.001). Micro-deletion frequency was greatest in azoospermic and severely oligoasthenozoospermic individuals (15% and 11.5%, respectively). AR CAG repeat length ranged from 9-38 CAG repeats in the normozoospermic population (n=98) and 13-31 CAG repeats in men with poor semen quality (n= 119). Variation in AR CAG trinucleotide repeat number was not significantly related to poor semen quality (P>0.05). Variation in POLγ CAG repeat number was not significantly different between normozoospermic men (n=93) and men with poor semen quality (n= 182); P>0.05. No nucleotide changes were observed in any of the three POLγ exonuclease motifs (n=83 normozoospermic and 191 non-normozoospermic motif, 61 and 65 motif II, and 60 and 64 motif III). Although most gene regions did not show an association with poor semen quality on their own, there was a general trend towards greater severity of impaired spermatogenesis with the presence of both Yq micro-deletion and mitochondrial DNA substitutions or moderately expanded AR CAG repeats. These results support the idea that male infertility is a complex process, due to many factors, some of which act dominantly and others act in concert