Phenotype in a patient with p.D50N mutation in GJB2 gene resemble both KID and Clouston syndromes

Connexins in epidermal health and diseases: insights into their mutations, implications, and therapeutic solutions

The epidermis, the outermost layer of the skin, serves as a protective barrier against external factors. Epidermal differentiation, a tightly regulated process essential for epidermal homeostasis, epidermal barrier formation and skin integrity maintenance, is orchestrated by several players, including signaling molecules, calcium gradient and junctional complexes such as gap junctions (GJs). GJ proteins, known as connexins facilitate cell-to-cell communication between adjacent keratinocytes. Connexins can function as either hemichannels or GJs, depending on their interaction with other connexons from neighboring keratinocytes. These channels enable the transport of metabolites, cAMP, microRNAs, and ions, including Ca2+, across cell membranes. At least ten distinct connexins are expressed within the epidermis and mutations in at least five of them has been linked to various skin disorders. Connexin mutations may cause aberrant channel activity by altering their synthesis, their gating properties, their intracellular trafficking, and the assembly of hemichannels and GJ channels. In addition to mutations, connexin expression is dysregulated in other skin conditions including psoriasis, chronic wound and skin cancers, indicating the crucial role of connexins in skin homeostasis. Current treatment options for conditions with mutant or altered connexins are limited and primarily focus on symptom management. Several therapeutics, including non-peptide chemicals, antibodies, mimetic peptides and allele-specific small interfering RNAs are promising in treating connexin-related skin disorders. Since connexins play crucial roles in maintaining epidermal homeostasis as shown with linkage to a range of skin disorders and cancer, further investigations are warranted to decipher the molecular and cellular alterations within cells due to mutations or altered expression, leading to abnormal proliferation and differentiation. This would also help characterize the roles of each isoform in skin homeostasis, in addition to the development of innovative therapeutic interventions. This review highlights the critical functions of connexins in the epidermis and the association between connexins and skin disorders, and discusses potential therapeutic options.

The Clinical Manifestation of p.Asp50Asn Heterozygous Mutation of GJB2 Gene in 3 Members of a Family Is Similar to That of Clouston Syndrome

Keratitis-ichthyosis-deafness (KID) syndrome has genetic heterogeneity, and the clinical manifestations of some patients may overlap with Clouston syndrome. A 34-year-old female patient came to our department with a complain of “sparse hair, rough skin, photophobia and deafness for more than 30 years.” We found that the proband and two other family members (57-year-old mother and 4-year-old daughter) had similar clinical manifestations: systemic hair loss, generalized skin hyperkeratosis, especially in the metacarpophalangeal area. Subungual hyperkeratosis, finger/toenail dystrophy, as well as photophobia and epiphora. According to the investigation, one of the family members also had similar clinical manifestations (grandfather of the proband) and he’s died. The other three members of the family had no hearing impairment, and all patients had typical nail dystrophy, hair loss and palmoplantar hyperkeratosis, similar like as seen in Clouston syndrome, so we suspected to diagnose the case as Clouston syndrome. However, after genetic testing, it was found that the proband, his mother and daughter all had p.Asp50Asn heterozygous mutations in the GJB2 gene, and no mutation was detected in GJB6. The modified diagnosis was KID syndrome.

Hereditary Hearing Impairment with Cutaneous Abnormalities

Syndromic hereditary hearing impairment (HHI) is a clinically and etiologically diverse condition that has a profound influence on affected individuals and their families. As cutaneous findings are more apparent than hearing-related symptoms to clinicians and, more importantly, to caregivers of affected infants and young individuals, establishing a correlation map of skin manifestations and their underlying genetic causes is key to early identification and diagnosis of syndromic HHI. In this article, we performed a comprehensive PubMed database search on syndromic HHI with cutaneous abnormalities, and reviewed a total of 260 relevant publications. Our in-depth analyses revealed that the cutaneous manifestations associated with HHI could be classified into three categories: pigment, hyperkeratosis/nail, and connective tissue disorders, with each category involving distinct molecular pathogenesis mechanisms. This outline could help clinicians and researchers build a clear atlas regarding the phenotypic features and pathogenetic mechanisms of syndromic HHI with cutaneous abnormalities, and facilitate clinical and molecular diagnoses of these conditions.