17q21.31 microdeletion syndrome: further expanding the clinical phenotype.

Microdeletions of the 17q21.31 region are associated with hypotonia, oromotor dyspraxia, an apparently characteristic face, moderate learning disability and have an estimated prevalence of approximately 1 in 16,000. Here we report 3 individuals who extend further the phenotypic spectrum observed with microdeletions of the 17q21.31 region. They all have learning disability, hypotonia, and craniofacial dysmorphism in keeping with previous reported cases. One case has iris-choroid coloboma and partial situs inversus, 2 features that are newly recorded phenotype abnormalities. These deletions were detected from a cohort of 600 individuals with learning disability and congenital anomalies, reflecting that 17q21.31 microdeletions are a common finding in such cases. FISH analysis demonstrated that each of the deletions occurred as de novo events. The deleted region in our cases encompasses the previously defined critical region for 17q21.31, and includes CRHR1 and MAPT, putative candidate genes for the 17q21.31 phenotype. The 17q21.31 microdeletion phenotype is perhaps more variable than previously described despite haploinsufficiency for the same genes in many cases.