Further delineation of KIDAR syndrome: Two new cases with novel variants, functional analysis of the variants and a comprehensive review

The syndrome known as KIDAR (keratitis, ichthyosis, deafness, autosomal recessive) is extremely rare. It is caused by biallelic mutations in AP1B1 , encoding adaptor-related protein complex, beta-1 subunit. AP1 complex takes part in the formation of vesicles and the selection of cargo proteins in the trans-golgi network. It also contributes to vesicular transport of ATP7A and ATP7B. Accordingly, KIDAR has been defined as both an adaptinopathy and a copper metabolism disorder. Eleven cases have been reported to date. We report two new KIDAR cases with novel splice site variants—c.1796+1 G > T and c.1796+1 G > C—in AP1B1 (NM_001127.4) gene. Functional analysis of the first variant revealed that this mutation disrupts the normal splicing process, resulting in the creation of a cryptic donor site 150 base pairs downstream of the canonical donor site which introduces a premature stop codon into the transcript. We also present a review of previously reported KIDAR cases and genetic disorders involving altering copper metabolism and highlight our patients’ new clinical features, which may broaden the recognized phenotype. A detailed study of these cases may contribute to the ongoing genetic and clinical characterization of KIDAR syndrome.