Deletion mapping of critical region for hypospadias, penoscrotal transposition and imperforate anus on human chromosome 13

Background: The 13q-deletion syndrome causes human congenital birth defects due to the loss of regions of one long arm of human chromosome 13. A distal critical region for severe genitourinary and anorectal birth defects in the region of 13q32.2-34 has been suggested; we sought to narrow this critical region. Methods: From patients with karyotypes revealing haploinsufficiency for distal chromosome 13q and their parents, peripheral blood was obtained and lymphocytes were immortalized for DNA isolation. Genetic and molecular cytogenetic methods were used to map deletions. Patient and parental samples were genotyped with a panel of 20 microsatellite markers spanning 13q31.3-qter and deletions identified by loss of heterozygosity. Deletions were also mapped using a panel of 35 BAC clones from the same region as probes for fluorescence in situ hybridization on patient lymphoblastoid metaphase preparations. The data were synthesized and a deletion map defining the critical region was generated. Results: Eight patients with known deletions around 13q32-qter and their parents were analyzed, and categorized into three groups: three patients without anorectal or genitourinary anomalies (hypospadias, penoscrotal transposition), four male patients with anorectal and/or genitourinary anomalies, and one XY patient with ambiguous genitalia without anorectal anomalies. We mapped the critical region for anorectal and genitourinary anomalies to an ∼9.5-Mb interval of 13q33.3-q34 delineated by markers D13S280-D13S285; this spans ∼8% of the chromosome and contains 20 annotated genes. Conclusion: The critical region of chromosome 13q mediating genitourinary/anorectal anomalies has been further narrowed to a ∼9.5 Mb region on 13q33.3-q34. Identification of the gene(s) mediating these syndromic genitourinary defects should further our knowledge on molecular mediators of non-syndromic hypospadias, penoscrotal transposition and anorectal malformations.