WNT10A, dermatology and dentistry

WNTs (Wingless-related integration sites) are secreted glycoproteins that are involved in signalling pathways critical to organ development and tissue regeneration. Of the 19 known WNT ligands, one member of this family, WNT10A, appears to have specific relevance to skin, its appendages and teeth. This review focuses on how variants in the WNT10A gene have been associated with various ectodermal disorders and how such changes may have clinical relevance to dermatologists and dentists. Germline mutations in WNT10A underlie several forms of autosomal recessive ectodermal dysplasia in which heterozygous carriers may also display some lesser ectodermal anomalies. Within the general population, multiple heterozygous variants in WNT10A can cause skin, hair, sweat gland or dental alterations, also known as ectodermal derivative impairments. WNT10A variants have also been implicated in hair thickness, male androgenetic alopecia, hair curl, acne vulgaris, lipodystrophy, keloids, wound healing, tooth size, tooth agenesis, hypodontia, taurodontism and oral clefting. Beyond dermatology and dentistry, WNT10A abnormalities have also been identified in kidney fibrosis, keratoconus, certain malignancies (particularly gastrointestinal) and neuropathic pain pathways. In this review, we detail how WNT10A is implicated as a key physiological and pathological contributor to syndromic and nonsyndromic disorders, as well as population variants, affecting the skin and teeth, and document all reported mutations in WNT10A with genotype-phenotype correlation.

Prevalence, pathophysiology and management of itch in epidermolysis bullosa

Epidermolysis bullosa (EB) is a highly diverse group of inherited skin disorders, resulting from mutations in genes encoding proteins of the dermoepidermal junction. Itch (pruritus) is one of the most common symptoms across all EB subtypes. It occurs in blistered or wounded sites, or manifests as a generalized phenomenon, thereby affecting both intact skin and healing wounds. The mechanism of pruritus in EB is unclear. It is likely that skin inflammation secondary to barrier disruption, wound healing cascades and dysregulated activation of epidermal sensory nerve endings are all involved in its pathophysiology on the molecular and cellular level. Understanding these mechanisms in depth is crucial in developing optimized treatments for people with EB and improving quality of life. This review summarizes current evidence on the prevalence, mechanisms and management of itch in EB.

Autosomal recessive hypotrichosis with loose anagen hairs associated with TKFC mutations

BACKGROUND

Loose anagen hair is a rare form of impaired hair anchorage in which anagen hairs that lack inner and outer root sheaths can be gently and painlessly plucked from the scalp. This condition usually occurs in children and is often self-limiting. A genetic basis for the disorder has been suggested but not proven. A better understanding the aetiology of loose anagen hair may improve prevention and treatment strategies.

OBJECTIVES

To identify a possible genetic basis of loose anagen hair using next-generation DNA sequencing and functional analysis of variants identified.

METHODS

In this case study, whole-exome sequencing analysis of a pedigree with one affected individual with features of loose anagen hair was performed.

RESULTS

The patient was found to be compound heterozygous for two single-nucleotide substitutions in TKFC resulting in the following missense mutations: c.574G> C (p.Gly192Arg) and c.682C> T (p.Arg228Trp). Structural analysis of human TKFC showed that both mutations are located near the active site cavity. Kinetic assays of recombinant proteins bearing either of these amino acid substitutions showed almost no dihydroxyacetone kinase or D-glyceraldehyde kinase activity, and FMN cyclase activity reduced to just 10% of wildtype catalytic activity.

CONCLUSIONS

TKFC missense mutations may predispose to the development of loose anagen hairs. Identification of this new biochemical pathobiology expands the metabolic and genetic basis of hypotrichosis.

A decade of next-generation sequencing in genodermatoses: the impact on gene discovery and clinical diagnostics

BACKGROUND

Discovering the genetic basis of inherited skin diseases is fundamental to improving diagnostic accuracy and genetic counselling. In the 1990s and 2000s, genetic linkage and candidate gene approaches led to the molecular characterization of several dozen genodermatoses, but over the past decade the advent of next-generation sequencing (NGS) technologies has accelerated diagnostic discovery and precision.

OBJECTIVES

This review examines the application of NGS technologies from 2009 to 2019 that have (i) led to the initial discovery of gene mutations in known or new genodermatoses and (ii) identified involvement of more than one contributing pathogenic gene in individuals with complex Mendelian skin disorder phenotypes.

METHODS

A comprehensive review of the PubMed database and dermatology conference abstracts was undertaken between January 2009 and December 2019. The results were collated and cross-referenced with OMIM.

RESULTS

We identified 166 new disease-gene associations in inherited skin diseases discovered by NGS. Of these, 131 were previously recognized, while 35 were brand new disorders. Eighty-five were autosomal dominant (with 43 of 85 mutations occurring de novo), 78 were autosomal recessive and three were X-linked. We also identified 63 cases harbouring multiple pathogenic mutations, either involving two coexisting genodermatoses (n = 13) or an inherited skin disorder in conjunction with other organ system phenotypes (n = 50).

CONCLUSIONS

NGS technologies have accelerated disease-gene discoveries in dermatology over the last decade. Moreover, the era of NGS has enabled clinicians to split complex Mendelian phenotypes into separate diseases. These genetic data improve diagnostic precision and make feasible accurate prenatal testing and better-targeted translational research.