Further delineation of the hypotrichosis-deafness syndrome

We recently delineated a novel disorder characterized by hypotrichosis, nail dystrophy and sensorineural deafness and caused by a missense mutation in GJB2 (connexin26). The patient, a girl, was two years old when we first saw her. We had the opportunity to re-examine her at four years of age and found that the phenotype had changed appreciably. The hypotrichosis was less pronounced, but the nail dystrophy had worsened. Intriguingly, the phenotype now included a mucositis and skin lesions identical to those found in erythrokeratodermia variabilis. There is now a considerable overlap with other gap junction disorders and we propose that some cases of erythrokeratodermia variabilis without mutations in either GJB3 or GJB4 but with deafness may be caused by mutations in GJB2. This is the first description of the evolution of a gap junction disease over time and we note that follow-up of patients suffering from gap junction skin disorders is necessary to fully delineate the phenotypes caused by mutations in gap junction genes.

An unusual N-terminal deletion of the laminin alpha3a isoform leads to the chronic granulation tissue disorder laryngo-onycho-cutaneous syndrome

Laryngo-onycho-cutaneous (LOC or Shabbir) syndrome (OMIM 245660) is an autosomal recessive epithelial disorder confined to the Punjabi Muslim population. The condition is characterized by cutaneous erosions, nail dystrophy and exuberant vascular granulation tissue in certain epithelia, especially conjunctiva and larynx. Genome-wide homozygosity mapping localized the gene to a 2 Mb region on chromosome 18q11.2 with an LOD score of 19.8 at theta=0. This region includes the laminin alpha3 gene (LAMA3), in which loss-of-expression mutations cause the lethal skin blistering disorder Herlitz junctional epidermolysis bullosa. Detailed investigation showed that this gene possesses a further 38 exons (76 exons in total) spanning 318 kb of genomic DNA, and encodes three distinct proteins, designated laminin alpha3a, alpha3b1 and alpha3b2. The causative mutation in 15 families was a frameshift mutation 151insG predicting a stop codon 7 bp downstream in an exon that is specific to laminin alpha3a. This protein is secreted only by the basal keratinocytes of stratified epithelia, implying that LOC is caused by dysfunction of keratinocyte-mesenchymal communication. Surprisingly, the 151insG mutation does not result in nonsense-mediated mRNA decay due to rescue of the transcript by an alternative translation start site 6 exons downstream. The resultant N-terminal deletion of laminin alpha3a was confirmed by immunoprecipitation of secreted proteins from LOC keratinocytes. These studies show that the laminin alpha3a N-terminal domain is a key regulator of the granulation tissue response, with important implications not only in LOC but in a range of other clinical conditions associated with abnormal wound healing.