LAUSR

Calpainopathies constitute a heterogeneous group of disorders resulting from deficiencies in calpains, calcium‐specific proteases that modulate substrates by limited proteolysis. Clinical manifestations depend on tissue‐specific expression of the defective calpain and substrate specificity. CAPN15, encoding the Drosophila small optic lobes (sol) homolog, was recently found to cause various eye defects in individuals carrying bi‐allelic missense variants. Here we report on two siblings with manifestations reminiscent of Johanson‐Blizzard syndrome including failure to thrive, microcephaly, global developmental delay, dysmorphic features, endocrine abnormalities and congenital malformations, in addition to eye abnormalities. Exome sequencing identified a homozygous 47 base‐pair deletion in a minimal intron of CAPN15, including the splice donor site. Sequencing of cDNA revealed single exon skipping, resulting in an out‐of‐frame deletion with a predicted premature termination codon. These findings expand the phenotypic spectrum associated with CAPN15 variants, and suggest that complete loss‐of‐function is associated with a recognizable syndrome of congenital malformations and developmental delay, overlapping Johanson‐Blizzard syndrome and the recently observed brain defects in Capn15 knockout (KO) mice. Moreover, the data highlight the unique opportunity for indel detection in minimal introns.