Microphthalmia with brain and digital anomalies (
MCOPS6, MIM# 607932) is an autosomal dominant disorder caused by loss-of-function variants or large deletions involving BMP4, which encodes
bone morphogenetic protein 4, a member of the TGF-β
protein superfamily. BMP4 has a number of roles in embryonic development including neurogenesis, lens induction, development of cartilage and bone, urogenital development, limb and digit patterning, hair follicle regeneration, as well as tooth formation. In addition to syndromic
microphthalmia, BMP4 variants have been implicated in non-syndromic
cleft lip with or without
cleft palate and
congenital healed cleft lip indicating different allelic presentations.
MCOPS6 subjects may also lack some of the major phenotypic hallmarks of the disorder, including
microphthalmia, indicating variable expressivity. As only a handful of individuals with
MCOPS6 have been described, we review the clinical findings in previously reported cases with either deletions or loss-of-function variants in BMP4. We describe three new cases, including two subjects with novel deletions and one subject with a likely pathogenic de novo nonsense variant [c.1052C>G, p.(S351*)] in BMP4. One of the subjects had dual molecular diagnoses including a co-occurring microdeletion at 17q21.31 associated with
Koolen de Vries syndrome, which has a partially overlapping disease phenotype. None of these individuals had clinically apparent
microphthalmia or anopthalmia, which have been reported in a majority of previously described cases. One subject had exophthalmia and
strabismus, while another had bilateral Peters anomaly and sclerocornea, thus expanding the phenotype associated with BMP4 loss-of-function variants.