Exome Sequencing to Identify Novel Susceptibility Genes for Nonsyndromic Split-Hand/Ft Malformation: A Report From...

Split-hand/foot malformation (SHFM) is a rare, genetically heterogeneous, congenital limb defect. Some but not all associated genes are known; therefore, the aim was to identify genes underlying SHFM.

Buccal cell-derived DNA from 26 children with SHFM and their parents who participated in the National Birth Defects Prevention Study was exome sequenced. Family-based trio analyzes prioritized rare coding variants by inheritance patterns, predicted pathogenicity, and location within putative limb development genes. Copy-number variants in SHFM candidate genomic regions were also examined. Case-control analyzes compared coding variants between case children and 1191 controls (parents of children with non-limb birth defects). Variant validation was by Sanger sequencing or droplet digital polymerase chain reaction.

In family-based analyzes, the prioritized and validated variants (each in a single family) included likely damaging variants that were heterozygous and de novo in speckle type BTB/POZ protein (SPOP) and ubiquitin-like modifier activating enzyme 2 (UBA2), X-linked recessive in fibroblast growth factor 13 (FGF13) and RNA binding motif protein 10 (RBM10), and compound heterozygous in interleukin enhancer binding factor 3 (ILF3). Validation assays did not confirm predicted de novo copy-number gains at chromosomes 10q24 and 19p13.11. Case-control analyzes did not identify statistically significant associations.

Exome analysis nominated new susceptibility genes (FGF13, ILF3, RBM10, SPOP) and detected a variant in a known candidate gene (UBA2). Follow-up investigation is needed to ascertain damaging variants in these genes in additional cases with SHFM and evaluate the impact of the variants on gene expression, protein function, and limb development.