22q13 deletion syndrome

22q13 deletion syndrome, also known as Phelan-McDermid syndrome, is a genetic disorder caused by deletions or rearrangements at the q terminal end, the long arm, of chromosome 22. Any abnormal variation in the q13 region that produces the significant features typical of a terminal deletion may be diagnosed as this syndrome, though researchers disagree about its exact definition. The Developmental Synaptopathies Consortium defines it by SHANK3 mutations, which appears to exclude terminal deletions. Large terminal deletions can be found by karyotype, but many are too small, so DNA microarray has become the usual diagnostic tool, with FISH still useful for mosaicism and chromosomal rearrangements.