Ring Chromosome 22

About 250 cases of ring chromosome 22 (RC22) have been reported in the literature. Approximately 90% of RC22 cases have a deletion of the terminal band, 22q13, compatible with the clinical diagnosis of Phelan-McDermid syndrome (PMS), previously called 22q13 deletion syndrome. The phenotype of these RC22 is consistent with PMS, with intellectual impairment, motor delays, neonatal hypotonia, absent or severely delayed speech, and minor dysmorphic features, although there is a greater predisposition to growth delay in RC22 than in simple deletion of 22q13. It is estimated that about 14% of individuals with PMS have a RC22 but this is likely to be an underestimate. Many individuals with deletion of 22q13 are now diagnosed by chromosomal microarray analysis (CMA), which does not detect the RC. A follow-up karyotype is required, and recommended, to detect the ring following the identification of a terminal deletion of chromosome 22 by CMA. It is imperative to determine if a ring is present, as the additional health risk of developing neurofibromatosis type 2 (NF2) and atypical teratoid rhabdoid tumors (ATRT) accompany the presence of a RC22 in individuals with PMS.