New intragenic and promoter region deletion mutations in FERMT1 underscore genetic homogeneity in Kindler syndrome

BACKGROUND

Kindler syndrome (KS) is a rare autosomal recessive skin disorder, which was recently reclassified as a subtype of epidermolysis bullosa. Despite the fact that loss-of-function mutations in the FERMT1 gene, encoding kindlin-1, have been shown to cause the syndrome in numerous patients, a small number of typical cases of KS in which FERMT1 mutations could not be identified has raised the possibility that the disorder may be genetically heterogeneous.

AIM

To assess two highly consanguineous families with clinical characteristics of KS.

RESULTS

In the first family, a hitherto unreported deletion (c.137-140delTAGT) in FERMT1 was detected, which is predicted to lead to premature termination of translation. However, direct sequencing of the coding region of FERMT1 failed to disclose any pathogenic change in the second family. To confirm the possibility that the disease in this family may be due to a mutation in another gene, we used homozygosity mapping, and found that all affected family members share a segment of homozygosity on 20p12.3, spanning the FERMT1 gene. Accordingly, a large and highly unusual deletion (g.-711-1241del) spanning the putative FERMT1 promoter sequence and the first noncoding exon of the gene was found to cosegregate with the disease phenotype in this family, and to prevent transcription of the gene, as attested by the lack of FERMT1 message in the skin of a patient.

CONCLUSION

The present data provide evidence in support of genetic homogeneity in KS.

CEDNIK syndrome results from loss-of-function mutations in SNAP29

BACKGROUND

CEDNIK (cerebral dysgenesis, neuropathy, ichthyosis and keratoderma) syndrome is a rare genodermatosis which was shown 5 years ago in one family to be associated with a loss-of-function mutation in SNAP29, encoding a member of the SNARE family of proteins. Decrease in SNAP29 expression was found to result in abnormal lamellar granule maturation leading to aberrant epidermal differentiation and ichthyosis.

OBJECTIVES

To delineate the molecular consequences of disease-causing mutations in SNAP29.

METHODS

We used direct sequencing, in vitro mutagenesis and three-dimensional organotypic cell cultures.

RESULTS

We identified a novel homozygous insertion in SNAP29 (c.486insA) in two sibs presenting with ichthyosis and dysgenesis of the corpus callosum. In vitro transfection experiments indicated that this mutation results in SNAP29 loss-of-function. Further substantiating this notion, we could replicate histological features typical for CEDNIK syndrome in three-dimensional primary human keratinocyte organotypic cell cultures downregulated for SNAP29.

CONCLUSIONS

The identification of a second mutation in SNAP29 in the present study definitely establishes a causal relationship between defective function of SNAP29 and the pleiotropic manifestations of CEDNIK syndrome. Our present and previous data position SNAP29 as an essential component of the epidermal differentiation machinery.