ZIC2 and holoprosencephaly: Although CMA was performed on all simplex cases (n = 141), a causal variant was identified in the form of chromosomal deletion in only three cases (14DG1134, 16DG1465, and 15DG0267); the latter is a case of holoprosencephaly linked to a large homozygous deletion that encompasses ZIC2 and ZIC5 (Additional file 1: Table S1, Additional file 2: Figure S3 A-B).