A HOXA13 allele with a missense mutation in the homeobox and a dinucleotide deletion in the promoter underlies Guttmacher syndrome

Abstract

Guttmacher syndrome, a dominantly inherited combination of distal limb and genital tract abnormalities, has several features in common with hand-foot-genital syndrome (HFGS), including hypoplastic first digits and hypospadias. The presence of features not seen in HFGS, however, including postaxial polydactyly of the hands and uniphalangeal 2(nd) toes with absent nails, suggests that it represents a distinct entity. HFGS is caused by mutations in the HOXA13 gene. We have therefore re-investigated the original Guttmacher syndrome family, and have found that affected individuals are heterozygous for a novel missense mutation in the HOXA13 homeobox (c.1112A>T; homeodomain residue Q50L), which arose on an allele already carrying a novel 2-bp deletion (-78-79delGC) in the gene's highly conserved promoter region. This deletion produces no detectable abnormalities on its own, but may contribute to the phenotype in the affected individuals. The missense mutation, which alters a key residue in the recognition helix of the homeodomain, is likely to perturb HOXA13's DNA-binding properties, resulting in both a loss and a specific gain of function.