Porokeratotic eccrine duct and hair follicle nevus (PEHFN) associated with keratitis-ichthyosis-deafness (KID) syndrome

Postzygotic gain-of-function variants in FGFR2 in two patients with hair follicle naevus

Hair follicle naevus (HFN) is a rare benign hamartoma that predominantly affects the face and neck. The genetic basis of HFN remains unclear. We report on two cases of HFN caused by pathozygotic gain-of-function variants in FGFR2.

Ichthyosis follicularis syndromes in patients with germline mutations in GJB2

Ichthyosis follicularis (IF) manifests as generalized spiny follicular projections found in syndromic diseases secondary to SREBF1 and MBTPS2 mutations. We sought the genetic cause of IF in two distinct families from a cohort of 180 ichthyosis patients. In Family 1, the proband presented with IF, bilateral sensorineural hearing loss (SNHL) and punctate palmoplantar keratoderma, and compound heterozygous GJB2 mutations were discovered in DNA from peripheral blood lymphocytes: GJB2:c.526A>G and c.35delG. In Family 2, the proband presented with a previously unreported IF phenotype in the context of KID syndrome, and whole-exome sequencing found a de novo heterozygous GJB2:c.148G>A mutation. Histopathology was consistent with porokeratotic eccrine ostial and dermal duct nevus (PEODDN) and IF in Probands 1 and 2, respectively. Our findings add to the clinical and histopathological spectrum of IF and emphasize the association of PEODDN-like entities with GJB2 variants.

Porokeratotic eccrine and hair follicle nevus: a report of two cases and review of the literature

Porokeratotic eccrine and hair follicle nevus is a very rare non-hereditary disorder of keratinization with eccrine and hair follicle involvement with only 9 cases described in the literature. In 2009 the term porokeratotic anexial ostial nevus was proposed to comprehend porokeratotic eccrine and hair follicle nevus and a related and more common process without follicular involvement: porokeratotic eccrine ostial and dermal duct nevus Recent findings suggest that both entities may be produced by a mutation in GJB2 gene, which is associated to KID syndrome. Herein we report 2 cases of porokeratotic eccrine and hair follicle nevus and review the existing cases in the Spanish and English literature.

Connexins and pannexins in the integumentary system: the skin and appendages

The integumentary system comprises the skin and its appendages, which includes hair, nails, feathers, sebaceous and eccrine glands. In this review, we focus on the expression profile of connexins and pannexins throughout the integumentary system in mammals, birds and fish. We provide a picture of the complexity of the connexin/pannexin network illustrating functional importance of these proteins in maintaining the integrity of the epidermal barrier. The differential regulation and expression of connexins and pannexins during skin renewal, together with a number of epidermal, hair and nail abnormalities associated with mutations in connexins, emphasize that the correct balance of connexin and pannexin expression is critical for maintenance of the skin and its appendages with both channel and non-channel functions playing profound roles. Changes in connexin expression during both hair and feather regeneration provide suggestions of specialized communication compartments. Finally, we discuss the potential use of zebrafish as a model for connexin skin biology, where evidence mounts that differential connexin expression is involved in skin patterning and pigmentation.

Connexin hemichannels influence genetically determined inflammatory and hyperproliferative skin diseases

Connexin mutations underlie numerous human genetic diseases. Several connexin genes have been linked to skin diseases, and mechanistic studies have indicated that a gain of abnormal channel function may be responsible for pathology. The topical accessibility of the epidermal connexins, the existence of several mouse models of human skin disease, and the ongoing identification of pharmacological inhibitors targeting connexins provide an opportunity to test new therapeutic approaches.

Disseminated superficial actinic porokeratosis on the face treated with imiquimod 5% cream

Porokeratoses are a group of hereditary or acquired disorders characterized by annular lesions with an atrophic center and a prominent peripheral ridge. Pathologically, porokeratosis is characterized by the presence of abnormal clones of keratinocytes that form a column of parakeratotic cells, called the cornoid lamella. Fifteen percent of patients of disseminated superficial actinic porokeratosis (DSAP) have facial lesions; other regions like the extensor surface of extremities constitute the majority of reported cases. Exclusively facial lesions are probably less frequent. Rarely, actinic porokeratosis is confined to the nose only. Of reported porokeratosis cases, 7.5% have revealed a malignancy arising within the lesion. We present a case of facial sporadic DSAP that was treated with imiquimod 5% cream in conjunction with a regular sunscreen. Follow-up of this case is important to rule out the possibility of malignant transformation of the lesions.

Porokeratotic eccrine nevus may be caused by somatic connexin26 mutations

Porokeratotic eccrine ostial and dermal duct nevus, or porokeratotic eccrine nevus (PEN), is a hyperkeratotic epidermal nevus. Several cases of widespread involvement have been reported, including one in association with the keratitis–ichthyosis–deafness (KID) syndrome (OMIM #148210), a rare disorder caused by mutations in the GJB2 gene coding for the gap junction protein connexin26 (Cx26). The molecular cause is, as yet, unknown. We have noted that PEN histopathology is shared by KID. The clinical appearance of PEN can resemble that of KID syndrome. Furthermore, a recent report of cutaneous mosaicism for a GJB2 mutation associated with KID describes linear hyperkeratotic skin lesions that might be consistent with PEN. From this, we hypothesized that PEN might be caused by Cx26 mutations associated with KID or similar gap junction disorders. Thus, we analyzed the GJB2 gene in skin samples from two patients referred with generalized PEN. In both, we found GJB2 mutations in the PEN lesions but not in unaffected skin or peripheral blood. One mutation was already known to cause the KID syndrome, and the other had not been previously associated with skin symptoms. We provide extensive functional data to support its pathogenicity. We conclude that PEN may be caused by mosaic GJB2 mutations.