Keratoderma-hypotrichosis-leukonychia totalis syndrome (KHLS) is an extremely rare, autosomal-dominant disorder characterized by severe skin hyperkeratosis, congenital alopecia and leukonychia totalis. The genetic defect underlying KHLS remained undetermined. By performing whole-exome sequencing in a family with KHLS, we identified a heterozygous mutation (c.23G>T [p.Gly8Val]) in GJA1, which cosegregated with the phenotype in the family. In an additional affected individual, we also found the identical de novo mutation which was absent in his unaffected family members. GJA1 encodes a gap junction protein connexin 43 (Cx43) which is ubiquitously expressed in various organs, including the epidermis and hair follicles. In vitro studies on HEK293 cells expressing Cx43Gly8Val found that the protein formed gap junction plaques between adjacent transfected cells, as observed in the wild-type. Dye-transfer experiments by microinjection of Lucifer yellow displayed functional gap junction of the Cx43Gly8Val mutant. Using patch clamp and Ca2+ imaging methods, we observed that the Cx43Gly8Val hemichannel had significantly more openings than Cx43WT, facilitating Ca2+ influx at resting potential. Such gain-of-function effect might result in cytoplasmic Ca2+ overload, accelerated apoptosis of keratinocytes and subsequent skin hyperkeratosis. Taken together, our results demonstrated that, with probably enhanced hemichannel activities, a mutation in GJA1 is linked to KHLS without extracutaneous involvement.