A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, February 2015 / Androgen Insensitivity Syndrome (AIS) is an X-linked disorder caused by mutations in the androgen receptor (AR) gene. The phenotype is variable and ranges from a complete feminine syndrome to simple gynecomastia. The phenotypes are described in terms of complete, partial and mild forms (CAIS, PAIS and MAIS). We describe novel and previously reported (recurrent) mutations in the AR gene for a family in which segregation of breast cancer (BC) and gynecomastia/MAIS is present. Methods: We studied a family of 16 members spanning four generations. Based on the presentation of symptoms, the family was divided into affected, unaffected, and control groups. Seven patients (six males diagnosed with MAIS and one female diagnosed with BC) formed the affected group, four genetically related individuals (two males and two females) formed the unaffected group and five genetically unrelated family members (one male and four females) served as controls. In each of these individuals, PCR amplification, cloning and the sequencing of exon 1 were carried out. Exons 2-8 were sequenced directly after PCR amplification. Exon 1 (CAG)n and (GGN)n repeats were classified according to their length: short (S) (n<23), long (L) (n>23) and wild type (WT) (n=23). Results: Part 1-The (CAG)n repeats varied among individuals and generations. In the 2nd generation, the unaffected male was S and the control female was WT. In the 3rd generation, three affected males were S, 2 of the controls were WT, one control was L and the other S. In the 4th generation, the 4 affected individuals were L, 1 of the unaffected was WT and the other 2 unaffected were L. Part 2- The (GGN)n variations also differed among individuals and generations. In the 2nd generation, the unaffected male and the control were S. In the 3rd generation, all three affected family members were S and among the controls, 1 was WT, 1 was L and 2 were S. In the 4th generation, 3 of the affected were S and one was WT and among the 3 unaffected, 2 were S and one was WT. Part 3- 30 unreported (novel) mutations as well as 13 recurrent (previously reported) mutations in exon 1 of the AR gene were identified. 17 novel and 5 reported mutations were identified in the affected group, 8 novel and 5 reported mutations, including one premature stop codon mutation, were identified in the related unaffected group and 7 novel and 4 reported mutations were found in the controls. Of the above-mentioned mutations, four mutations were identified in the activation function-1 (AF-1) domain of exon 1 in 4 members (3 affected: M-2, F-1 and 1 unaffected: F-1) of the family. All the point mutations identified were somatic in nature and were present in heterogeneous form i.e wild and mutant (mixture) as determined by cloning. The analysis of exons 2 through 8 revealed completely WT sequences. Conclusions: The (CAG)n and (GGN)n repeat analysis showed an indeterminate association with MAIS and BC in the family. Generation specific patterns of (CAG)n were detected and suggest generation specific modulation of the AR. Novel mutations including AF-1 region mutations were identified in exon 1. The disruption of the AF-1 domain may affect the transactivation activity of the AR.