A Frameshift Mutation in PEN-2 Causes Familial Comedones Syndrome.

BACKGROUND: Familial comedones without dyskeratosis are a rare autosomal dominant skin disorder, characterized by the occurrence of comedones that are distributed all over the body with specific features. We have previously reported two Thai families with familial comedones with expanded phenotypic spectrum. However, its genetic defect and pathogenesis remain unknown. OBJECTIVE: To explore the molecular defect causing familial comedones. METHODS: Whole-genome linkage analysis and whole-exome sequencing in family I were performed. RESULTS: We identified a heterozygous one-base pair insertion, c.84_85insT (p. L28FfsX93) in PEN-2, located within the linked region on chromosome 19. PCR-Sanger sequencing confirmed the identified mutation. The mutation segregated with the disease phenotype in family I and was fully penetrant. This similar mutation was also present in the unrelated affected individual from family II. Quantitative PCR revealed increased mRNA expression of PEN-2 in leukocytes of affected individuals. CONCLUSION: We for the first time identify PEN-2 as the causative gene of familial comedones.

Expanding phenotypic spectrum of familial comedones.

Familial comedones is a rare autosomal dominant disorder characterized by thousands of comedones developing in teens. Some pits or inflammatory lesions may coexist. Only 32 patients from three families have previously been reported. We report herein 12 cases in two unrelated families with familial comedones. Clinical manifestations among members in the same family vastly vary from scattered comedones on the face, trunk, upper and lower extremities to generalized thousands of open comedones, a large number of skin pits and acneiform inflammatory lesions over the entire body. Additionally, multiple severe purulent nodules and abscesses that leave unsightly scars similar to those of hidradenitis suppurativa are observed. Lesions of long-standing inflammation in two patients had developed into squamous cell carcinoma with a poor prognosis. The phenotypic spectrum of familial comedones varies to a large degree. Most importantly, there is potential for some long-standing inflammatory lesions to develop into squamous cell carcinoma. Extra vigilance in surveillance and prompt treatment for such lesions are recommended.

Novel CTSK mutation resulting in an entire exon 2 skipping in a Thai girl with pycnodysostosis.

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia characterized by osteosclerosis, short stature, acro-osteolysis of the distal phalanges, bone fragility and skull deformities. Mutations in the cathepsin K (CTSK) gene, which encodes a lysosomal cysteine protease highly expressed in osteoclasts, have been found to be responsible for the disease. We identified a Thai girl with pycnodysostosis. Her parents were first cousins. Polymerase chain reaction sequencing of the entire coding regions of CTSK of the proband's complementary DNA revealed that the whole exon 2 was skipped. We subsequently amplified exon 2 using genomic DNA, which showed that the patient was homozygous for a c.120G>A mutation. The mutation was located at the last nucleotide of exon 2. Its presence was confirmed by restriction enzyme analysis using BanI. The skipping of exon 2 eliminates the normal start codon. The mutation has never been previously reported, thus the current report expands the CTSK mutational spectrum.