Basan Syndrome is an autosomal dominant genodermatosis characterized by congenital adermatoglyphia, transient congenital facial milia, neonatal acral bullae, and absent or reduced sweating. Basan Syndrome is rare and has been reported in only 10 kindreds worldwide. It is caused by variants in the skin-specific isoform of SMARCAD1, which starts with an alternative exon 1. All reported variants, except for one large deletion, are point mutations within the donor splice site of the alternative exon 1.
Here we report two families with Basan syndrome and describe two SMARCAD1 variants. In one family, we have identified a complex structural variant (a deletion and a non-tandem inverted duplication) using whole genome optical mapping and whole genome sequencing. Although this variant results in the removal of the first 9 exons of SMARCAD1 and exon 1 of the skin-specific isoform, it manifested in the typical Basan phenotype. This suggests that, unlike the skin-specific isoform, a single copy of SMARCAD1 full-length is sufficient for its respective function. In the second family, whole exome sequencing revealed a deletion of 12-bp spanning the exon/intron junction of the alternative exon 1 of the skin-specific SMARCAD1 isoform.
In conclusion, we report two additional families with Basan syndrome and describe two SMARCAD1 pathogenic variants.