OSR2 and microcephaly: Concordant polymorphisms for QTL 4 were intergenic or located in the genes VPS13B and OSR2. In humans, mutations in VPS13B cause the Cohen syndrome, for which symptoms include mental retardation, facial dysmorphism, microcephaly, retinal dystrophy, truncal obesity, joint laxity and intermittent neutropenia[24].