Phenotypic variability in a family with Townes-Brocks syndrome.

Townes-Brocks syndrome (TBS) is an autosomal dominant disorder characterized by external ear anomalies with sensorineural hearing loss, limb anomalies, renal and anorectal malformations. TBS is caused by mutations in SALL1, a gene mapped to chromosome 16q12.1. We report three generations of a family with SALL1 c.1326delC (p.Ser442fs) mutation, showing increased clinical severity over generations. The members of the first generation demonstrated polydactyly and deafness. In the second generation, the mother and uncle of the proband additionally had renal and/or anal anomalies. The proband in the third generation showed the most severe symptoms including congenital heart disease. Increase in clinical severity in successive generations in TBS cannot be explained genetically. There is wide clinical variation in TBS; however, most affected parents are usually mildly affected and may have similarly or more severely affected children. Social and/or physical bias at reproduction may contribute to an apparent increase in clinical severity over generations in TBS.