A novel missense mutation in RSPO4 gene underlies autosomal recessive congenital anonychia in a consanguineous Pakistani family

GLY67ARG substitution in RSPO4 disrupts the WNT signaling pathway due to an abnormal binding pattern with LGRs leading to anonychia

R-Spondins regulate the WNT/β-catenin signaling pathway by interacting with leucine rich-repeat containing G-protein coupled receptors (LGR4–6).

Genetics of human isolated hereditary nail disorders

Human hereditary nail disorders constitute a rare and heterogeneous group of ectodermal dysplasias. They occur as isolated and/or syndromic ectodermal conditions where other ectodermal appendages are also involved, and can occur associated with skeletal dysplasia. 'Nail disorder, nonsyndromic congenital' (OMIM; Online Mendelian Inheritance in Man) is subclassified into 10 different types. The underlying genes identified thus far are expressed in the nail bed and play important roles in nail development and morphogenesis. Here, we review the current literature on nail disorders and present a coherent review on the genetics of nail disorders. This review will pave the way to identifying putative genes and pathways involved in nail development and morphogenesis.

Structural and molecular basis of ZNRF3/RNF43 transmembrane ubiquitin ligase inhibition by the Wnt agonist R-spondin

The four R-spondin (Rspo) proteins are secreted agonists of Wnt signalling in vertebrates, functioning in embryogenesis and adult stem cell biology. Through ubiquitination and degradation of Wnt receptors, the transmembrane E3 ubiquitin ligase ZNRF3 and related RNF43 antagonize Wnt signalling. Rspo ligands have been reported to inhibit the ligase activity through direct interaction with ZNRF3 and RNF43. Here we report multiple crystal structures of the ZNRF3 ectodomain (ZNRF3(ecto)), a signalling-competent Furin1-Furin2 (Fu1-Fu2) fragment of Rspo2 (Rspo2(Fu1-Fu2)), and Rspo2(Fu1-Fu2) in complex with ZNRF3(ecto), or RNF43(ecto). A prominent loop in Fu1 clamps into equivalent grooves in the ZNRF3(ecto) and RNF43(ecto) surface. Rspo binding enhances dimerization of ZNRF3(ecto) but not of RNF43(ecto). Comparison of the four Rspo proteins, mutants and chimeras in biophysical and cellular assays shows that their signalling potency depends on their ability to recruit ZNRF3 or RNF43 via Fu1 into a complex with LGR receptors, which interact with Rspo via Fu2.

Novel missense mutation in the RSPO4 gene in congenital hyponychia and evidence for a polymorphic initiation codon (p.M1I)

Background

Anonychia/hyponychia congenita is a rare autosomal recessive developmental disorder characterized by the absence (anonychia) or hypoplasia (hyponuchia) of finger- and/or toenails frequently caused by mutations in the R-spondin 4 (RSPO4) gene.

Methods

Three hypo/anonychia consanguineous Pakistani families were ascertained and genotyped using microsatellite markers spanning the RSPO4 locus on chromosome 20p13. Mutation screening of the RSPO4 gene was carried out by direct sequencing of the entire coding region and all intron-exon boundaries.

Results

Mutations in the RSPO4 gene were identified in all families including a novel missense mutation c.178C>T (p.R60W) and two recurrent variants c.353G>A (p.C118Y) and c.3G>A (p.M1I). The c.3G>A variant was identified in unaffected family members and a control sample in a homozygous state.

Conclusions

This study raises to 17 the number of known RSPO4 mutations and further expands the molecular repertoire causing hypo/anonychia. The c.353G>A emerges as a recurrent change with a possible founder effect in the Pakistani population. Our findings suggest that c.3G>A is not sufficient to cause the disorder and could be considered a polymorphism.

Brachydactyly, anonychia and a deformed nasal tip in a 16-year-old girl: a case report

The current report describes a case of a 16-year-old girl with a rare combination of nasal dysmorphology, anonychia and brachydactyly of hands and feet. The combination of hand and nasal malformations suggested a type B brachydactyly. Genetic investigation, however, revealed Cooks syndrome with unexplained facial dysmorphology. Concerning her cosmetic complaints, options for surgical treatment were discussed. It was decided to treat only the nasal deformity by open rhinoplasty, leaving the nail deformities undisturbed.