Role of phosphoinositide-specific phospholipase C η2 in isolated and syndromic mental retardation.

Deletions in the distal region of the short arm of chromosome 1 (1p36) are widely diffuse, both as somatic abnormalities in tumors and as constitutive in the congenital 1p36 deletion syndrome. The deletion size varies from 1.5 to 10 Mb, with common breakpoints located from 1p36.13 to 1p36.33. Patients bearing constitutional deletion of a smaller region, 1p36.3, present with a number of features, including mental retardation. The gene PLCH2, codifying for the phosphoinositide-specific phospholipase C (PI-PLC) η2, maps on the 1p36.32 region. PI-PLC η2, expressed in the brain after birth, is a key enzyme in cellular calcium mobilization. In the brain, calcium plays a role in axon growth and retraction, growth cone guidance, synapse formation, and responses to various neurotransmitters. For its role in the nervous system, PI-PLC η2 might be a putative candidate gene for the neurodevelopmental delay observed in patients bearing 1p36.3 deletions.