A novel ZRS mutation leads to preaxial polydactyly type 2 in a heterozygous form and Werner mesomelic syndrome in a homozygous form

Abstract

Point mutations in the zone of polarizing activity regulatory sequence (ZRS) are known to cause human limb malformations. Although most mutations cause preaxial polydactyly (PPD), triphalangeal thumb (TPT) or both, a mutation in position 404 of the ZRS causes more severe Werner mesomelic syndrome (WMS) for which malformations include the distal arm or leg bones in addition to the hands and/or feet. Of more than 15 reported families with ZRS mutations, only one homozygous individual has been reported, with no change in phenotype compared with heterozygotes. Here, we describe a novel point mutation in the ZRS, 402C>T (AC007097.4:g.105548C>T), that is transmitted through two Mexican families with one homozygous individual. The homozygous phenotype for this mutation, WMS, is more severe than the numerous heterozygous individuals genotyped from both families who have TPT and PPD. A mouse transgenic enhancer assay shows that this mutation causes an expansion of the enhancer's expression domain in the developing mouse limb, confirming its pathogenicity. Combined, our results identify a novel ZRS mutation in the Mexican population, 402C>T, and suggest that a dosage effect exists for this ZRS mutation.

Keywords: SHH; Werner mesomelic syndrome; ZRS; enhancer; preaxial polydactyly.

Figure 1

A: The pedigree of family A contains 154 individuals; 31 have isolated TPT, 14 have PPD with TPT and only one (V/29) has WMS. B: The proband’s father (IV/30) has bilateral TPTs and a preaxial remnant with a small bone that he is able to manipulate. C: The proband’s mother (IV/31) has digitalization of thumbs with an extra crease in the distal interphalangeal space and bilateral elongated distal phalanx of first fingers. D–F: The proband (V/29) was born with PPD and after surgery has rudimentary thumbs. She has mild shortening and fusion of radioulnar bones, fusion of metacarpal bones and bilateral hypoplastic tibias with bowing of the fibula. G: The five-generation pedigree of family B contains two individuals with PPD, six individuals with isolated TPT, two individuals with PPD and TPT, and two individuals with mild radioulnar synostosis. H: The proband and siblings have bilateral TPTs, V/11 is shown here.

Figure 2

A: Chromatogram traces show the heterozygous mutation in the father (IV/30) and the homozygous mutation in the proband of family A compared with a wild-type control sample. The site of the mutation is indicated by the red arrow. B: The ZRS402C>T mutant transgenic enhancer assay shows the expanded anterior expression of LacZ beyond the posterior of the limb buds of a representative E11.5 mouse embryo. C: The isolated right hindlimb clearly shows enhancer expression beyond the normal ZPA region (indicated by the gray arrowhead) toward the anterior part of the limb (arrow). D: A control wild-type ZRS mouse assay shows LacZ confined to the normal ZPA region (gray arrowhead).