Genetics – Phelan-McDermid Syndrome Foundation

Ring Chromosome 22

Learn why ring chromosome 22 matters for individuals with Phelan-McDermid syndrome (PMS). While most people with PMS caused by a deletion have a terminal 22q13 deletion, approximately 10% have a ring chromosome 22, in which the ends of chromosome 22 join to form a circle. This blog explains why families should know whether a loved one with a terminal deletion has ring 22 and why a karyotype or FISH testing may be needed to identify it. Ring chromosome 22 can have additional medical implications, including an increased risk for tumors associated with loss of function of the NF2 gene and NF2-related schwannomatosis. Understanding a person’s genetic diagnosis can help families and healthcare providers discuss appropriate medical monitoring and recognize potential concerns earlier. Families affected by Phelan-McDermid syndrome can learn what testing identifies ring chromosome 22 and why follow-up with genetics and other specialists may be important.

Uncovering New Genotype-Phenotype Relationships in Phelan-McDermid Syndrome

Phelan-McDermid syndrome is a rare genetic condition usually caused by a deletion or structural change at the end of chromosome 22, in a region called 22q13. Symptoms and severity can vary widely among people with Phelan-McDermid syndrome. For individuals with a chromosome 22 deletion, the size of the deletion may help explain some of these clinical differences. In general, larger 22q13 deletions are associated with more significant developmental delays and medical concerns. A recent study in 63 people with Phelan-McDermid syndrome further explored these genotype-phenotype relationships, helping researchers better understand how chromosome 22 deletion size may influence symptoms such as language development, motor function and development, and social behaviors as well as medical issues. This study also identified several candidate genes that could also be contributing to the symptoms seen in Phelan-McDermid syndrome.