GDF5 is a second locus for multiple-synostosis syndrome

Abstract

Multiple-synostosis syndrome is an autosomal dominant disorder characterized by progressive symphalangism, carpal/tarsal fusions, deafness, and mild facial dysmorphism. Heterozygosity for functional null mutations in the NOGGIN gene has been shown to be responsible for the disorder. However, in a cohort of six probands with multiple-synostosis syndrome, only one was found to be heterozygous for a NOGGIN mutation (W205X). Linkage studies involving the four-generation family of one of the mutation-negative patients excluded the NOGGIN locus, providing genetic evidence of locus heterogeneity. In this family, polymorphic markers flanking the GDF5 locus were found to cosegregate with the disease, and sequence analysis demonstrated that affected individuals in the family were heterozygous for a novel missense mutation that predicts an R438L substitution in the GDF5 protein. Unlike mutations that lead to haploinsufficiency for GDF5 and produce brachydactyly C, the protein encoded by the multiple-synostosis-syndrome allele was secreted as a mature GDF5 dimer. These data establish locus heterogeneity in multiple-synostosis syndrome and demonstrate that the disorder can result from mutations in either the NOGGIN or the GDF5 gene.

Figure 1

A, Pedigree of family R02-328 with SYNS1. B, Chromatograms showing the GDF5 wild-type (WT) sequence and the nucleotide substitution, 1313G→T, predicted to lead to the amino acid substitution R438L.

Figure 2

Synthesis and secretion of normal and mutant GDF5 proteins. DF-1 cells transfected were control vector, human GDF5, chicken (ch) GDF5, ch R438C-GDF5, and ch R438L-GDF5. A, Ponceau red-stained western blot demonstrating protein expression and uniform loading in samples derived from the cell lysate and supernatant. B, Western blot analysis of lysate from ch GDF5 transfected cells showing pro-GDF5 in the human control lane and mature GDF5 in wild-type ch GDF5 and in ch R438L-GDF5 but not in ch R438C-GDF5 (top); western blot analysis of supernatant from ch GDF5–transfected cells showing pro-GDF5 in the human control lane and mature GDF5 in wild-type ch GDF5 and in ch R438L-GDF5 but not in ch R438C-GDF5 (bottom).