UCLA

Disorders of Sex Development (DSD) are defined as “congenital conditions in which development of chromosomal, gonadal, or anatomic sex is atypical.” These conditions have an approximate frequency of 0.5-1% of live births and encompass a wide variety of urogenital abnormalities ranging from mild hypospadias to sex reversal. Lack of standardized anatomical/endocrine phenotyping and the limited number of known DSD genes with poor genotype/phenotype correlation have hampered the field of clinical management, leaving many patients without a definitive genetic diagnosis. Thus, the focus of this thesis is to identify the underlying pathogenic genetic mutations that disrupt development of urogenital structures, leading to Disorders of Sex Development in humans.

The traditional trend of diagnostic approach for patients with DSD is to select candidate gene testing by searching for additional phenotypic and metabolic information through imaging studies and endocrine tests that could explain the patient’s phenotype. This approach is usually ineffective, costly and time-consuming. To address this issue and identify genetic variants leading to DSD, we utilized exome sequencing, in patients diagnosed with abnormal sex development. We show that exome sequencing has transformed the field of clinical genetic diagnosis by increasing the rate of diagnosis by approximately 30% and has become a method of choice for many clinicians.

Although exome sequencing provides much higher diagnostic yields for DSD patients than the conventional techniques, more than half of the patients tested with ES still do not possess a specific genetic diagnosis. Rather, in these patients ES identifies hundreds of variants of unknown clinical significance (VUS). To investigate the role of these variants in the 46,XY subset of DSD patients, we performed gonadal gene expression studies in C57BL/6J-YPOS mice modeling the phenotype of human 46,XY individuals to identify genes important in sex development. We used these genes to filter VUS identified in 46,XY DSD exome negative cases. We identified 15 novel candidate genes with mutations in 46,XY DSD patents that may be associated with disease pathogenesis.

Due to innate limitations of exonic short read sequencing, many native variants are not identified by exome sequencing. To this end, we utilize genome sequencing in conjunction with a novel genome mapping technology in order to uncover the full spectrum of variations present in a human genomes. Collectively, these two technologies provide a physical map and a base pair-level DNA resolution allowing for identification of novel pathogenic variants that were previously inaccessible.