The spectrum of mutations in erythrokeratodermias - novel and de novo mutations in GJB3

Abstract

Intercellular channels in skin are a complex and functionally diverse system formed by at least eight connexins (Cx). Our recent molecular studies implicating Cx defects in inherited skin disorders emphasize the critical role of this signaling pathway in epidermal differentiation. Erythrokeratodermia variabilis (EKV) is an autosomal dominant genodermatosis with a striking phenotype characterized by the independent occurrence of transient localized erythema and hyperkeratosis. The disease maps to 1p34-p35, and recently we identified the causative gene GJB3 encoding Cx31. We have now investigated GJB3 in two families and three sporadic cases with EKV, and report three new heterozygous mutations. In a sporadic case, we detected a mutation leading to substitution of a conserved phenylalanine (F137L) in the third transmembrane domain, which likely interferes with the proper assembly or gating properties of connexons. In another family, all three affected individuals carried two distinct mutations on the same GJB3 allele. However, only a de novo heterozygous missense mutation replacing arginine 42 with proline (R42P) co-segregated with the disease, while a 12 bp deletion predicted to eliminate four amino acid residues in the variable carboxy terminal domain of Cx31 was also found in clinically unaffected relatives but not in 90 unaffected controls. Including the previously published mutations, in toto, five different missense mutations have now been detected in 6 out of 17 families investigated by our laboratory, all of which presumably affect the cytoplasmic amino terminal and transmembrane domains of Cx31. In contrast, two mutations linked to progressive high-tone hearing impairment were located in the second extracellular domain, suggesting that the character and position of Cx mutations determine their phenotypic expression in different tissues. However, the phenotypic spectrum of GJB3 mutations seems not to include progressive symmetric erythrokeratodermia, another dominant genodermatosis with overlapping features, since no mutations were found in six unrelated families tested.

A common frameshift mutation and other variants in GJB4 (connexin 30.3): Analysis of hearing impairment families

“…To date fourteen human connexin genes have been described, several of which have been associated with human disorders. Four genes causing deafness (GJB1 (Cx32), GJB2 (Cx26), GJB3 (Cx31) and GJB6 (Cx30)) encode connexin proteins (http://www.iro.es/deafness) and distinct dominant mutations in three of these genes (GJB3, GJB2 and GJB6) are involved in skin diseases (reviewed in Kelsell et al, 2001 andRichard et al, 2000). Recently a mutation (F137L) in GJB4 (MIM# 605425) has been identified in affected members of a family with erythrokeratodermia variabilis (EKV; MIM#1 33200) (Macari et al, 2000) but the role of GJB4 in skin disorders has to be confirmed with the identification of additional EKV families with GJB4 mutations.…”

Properties of human connexin 31, which is implicated in hereditary dermatological disease and deafness

“…Connexin 31 (Cx31) is one of several connexins associated with human disease (see Supporting Text, which is published as supporting information on the PNAS web site, for further details and references). Cx31 is expressed in skin (1,2), and mutations in the human gene (GJB3) are associated with the genetic skin disorder erythrokeratodermia variabilis (3,4). Cx31 is also expressed in the mouse cochlea (5,6) and in peripheral auditory nerves (7), which may explain the association of some mutations in Cx31 with deafness (8).…”

“…Similarly, studies of human Cx31 (hCx31) suggest that mutations in this connexin may also lead to alterations in trafficking or channel function (26)(27)(28), and some mutations increase cell death when expressed in HeLa, NIH 3T3, or NEB1 cells (26,29). Although mutations in the gene for hCx31 have been associated with autosomal recessive deafness (30) or skin disease (31), most pathogenic hCx31 mutations lead to dominantly inherited disease (3,4,30) and are likely to be caused by either toxic gain-of-function or dominant-negative interactions.…”

Connexins: a connection with the skin

“…Mutations in the Cx gene GJB3 encoding Cx31 were identified in the autosomal dominant skin disorder erythrokeratodermia variabilis (EKV, OMIM 133200) (23), and simultaneously molecular defects in GJB2 (Cx26) were linked to palmoplantar keratoderma associated with congenital hearing loss (OMIM 148350) (18). Subsequent mutation reports of GJB3 in EKV (24,25) and the identification of a common GJB2 mutation (D66H) that underlies mutilating keratoderma with sensorineural deafness (Vohwinkel syndrome, OMIM 124500) (26) tighten this link and provide convincing evidence that gap junctional intercellular communication (GJIC) mediated by Cx signaling is crucial for normal function and differentiation of human skin. These observations then raise the questions: What are connexins and what is their role in skin?…”

“…In subsequent studies, GJB3 was screened for disease-causing mutations in 7 additional families with EKV and 6 families with PSEK (Table 4, Fig. 2) (24). While no molecular changes were found in PSEK, they identified 4 novel heterozygous se- quence aberrations in EKV.…”