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.