A novel variant in AFF3 underlying isolated syndactyly

Isolated syndactyly is a common limb malformation with limited known genetic etiology. We used exome sequencing to discover a novel heterozygous missense variant c.2915G > C: p.Arg972Pro in AFF3 on chromosome 2q11.2 in a family with isolated syndactyly in hands and feet. AFF3 belongs to a family of nuclear transcription activating factors and is involved in limb dorsoventral patterning. The variant Arg972Pro is located near the C terminus, a region that is yet to be associated with human disorders. Functional studies did not show a difference in the stability or subcellular localization of the mutant and wild type proteins. Instead, overexpression in zebrafish embryos suggests that Arg972Pro is a loss-of-function allele. These results suggest that variants in the C terminus of AFF3 may cause a phenotype distinct from previously characterized AFF3 variants.