22q13.3 deletion syndrome,
also known as Phelan-McDermid syndrome, is a chromosome abnormality caused by the loss (deletion) of a small piece of chromosome 22. The deletion occurs near the end of the long arm (or q arm) at a location designated as q13.3. The signs and symptoms of this condition vary widely from person to person. Common symptoms include low muscle tone (hypotonia), intellectual disability, delayed or absent speech, abnormal growth, tendency to overheat, large hands, and abnormal toenails. Affected individuals may have characteristic behaviors, such as mouthing or chewing on non-food items, decreased perception of pain, and autistic-like behaviors. The loss of a particular gene on chromosome 22, called the SHANK3 gene, is likely responsible for many of the signs and symptoms of 22q13.3 deletion syndrome. Additional genes within the deleted region probably contribute to the variable features of the syndrome. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.