Definition:

1p36 deletion syndrome is a recently delineated disorder, considered to be the most common subtelomeric microdeletion syndrome. 1p36 deletion syndrome is characterized by typical craniofacial features consisting of straight eyebrows, deep-set eyes, midface hypoplasia, wide and depressed nasal bridge, long philtrum, and pointed chin. Developmental delay/intellectual disability of variable degree and hypotonia are present in almost all patients. Seizures occur in around half of affected individuals. Other findings include structural brain abnormalities, congenital heart defects, eye/vision problems, hearing loss, skeletal anomalies, abnormalities of the external genitalia, and renal abnormalities. There is significant phenotypic variation among affected individuals. This variation is due, at least in part, to the genetic heterogeneity seen in 1p36 deletions which include terminal and interstitial deletions of varying lengths.