Implications for genotype-phenotype predictions in Townes-Brocks syndrome: case report of a novel SALL1 deletion and review of the literature.

Townes-Brocks syndrome (TBS) is a well-described genetic syndrome characterized by anal, ear, and thumb anomalies and variable expressivity. Over 60 nonsense and frameshift mutations have been identified in SALL1, the zinc finger transcription factor causing TBS, and are proposed to cause disease via a dominant negative mechanism. In contrast, only four deletions have been described, with mild phenotypes reported as a result of haploinsufficiency. We report on a family with features of TBS in whom a novel 149 kb deletion spanning the SALL1 gene was identified by high resolution cytogenetics SNP microarray. We review the available genotype-phenotype information for all known truncating mutations and deletions. Taken together, they do not support the correlation of SALL1 deletions with a milder TBS phenotype and highlight a need for more robust clinical phenotyping combined with investigation of mutational mechanism.