The urofacial (Ochoa) syndrome (UFS) is a rare autosomal recessive disorder characterized by abnormal facial expression and urinary abnormalities. Previously, we mapped the gene to a genomic interval of approximately 1 cM on chromosome region 10q23-24, using families from Columbia. Here we demonstrate genetic homogeneity of the syndrome through homozygosity mapping in American patients with Irish heritage. We established a physical map and identified novel polymorphic markers in the UFS critical region. Haplotype analysis using the new markers mapped the UFS gene within one YAC clone of 1,410 kb. We also determined the precise location of the gene encoding for glutamate oxaloacetate transaminase (GOT1) within the new UFS critical region and determined its genomic structure. However, mutation analysis excluded GOT1 as a candidate for the UFS gene.