Based on genetic data at least three entities may exist but they are discussed in this database as a group because so few families have been reported.  MCOPCT1 follows an autosomal dominant pattern and segregates with a single unknown mutation at 16p13.3.  Another family with a reciprocal translocation t(2;16)(p22.3;p13.3)  involving a breakpoint in the 16p13.3 region seems to support the idea that an altered gene in this location is responsible for the phenotype.  MCOPCT2 also usually follows an autosomal dominant pattern and seems to be caused by mutations in the SIX6 [1] gene (14q23.1).  The mode of inheritance in MCOPCT3 is uncertain since the transmission pattern in one family suggested X-linked dominance while in another family only males were affected.  No mutation or locus has been identified.