Recognizing a common genetic syndrome: 22q11.2 deletion syndrome

An article in published in the February 12th edition of the Canadian Medical Association Journal. To download the entire article (PDF) click here.

Below is a quote from the article authored by Ronak K. Kapadia, BSc,* and Anne S. Bassett, MD.**

*Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia.
**Clinical Genetics Research Program, Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, Toronto, Ontario.

22q11.2 deletion syndrome, previously known as DiGeorge syndrome or velocardiofacial syndrome, is the most common microdeletion syndrome known (estimated prevalence of 1 in 4000 live births), yet it remains underrecognized, especially in adults (1,2). Clinical variability, multisystem disease, subtle features, lack of medical genetics services, the recent availability of molecular cytogenetic testing in 1994 and, most importantly, the unfamiliarity of clinicians with this syndrome all contribute to delayed and missed diagnoses. Clinic visits and admissions to hospital present opportunities to diagnose 22q11.2 deletion syndrome, but without knowledge of this syndrome and its features, patients will not receive the correct diagnosis.

The deletion is hemizygous (affecting only 1 chromosome) and involves the 22q11.2 region of the long arm of chromosome 22. In most newly diagnosed cases (> 90%), and in our case, the parents are unaffected because this is a de novo mutation. Both parents of patients with 22q11.2 deletion syndrome should be tested for the deletion because expression may be mild (1). Fertility is generally unaffected in individuals with 22q11.2 deletion syndrome. Patients with a confirmed diagnosis require genetic counselling about the 50% chance of transmitting the deletion with each pregnancy and about the wide range of congenital and later-onset conditions associated with this syndrome (1). Common later-onset conditions include endocrine disorders, such as hypothyroidism and hypoparathyroidism (1), and schizophrenia or schizoaffective disorder (about 25% of cases) (1,2).

Bold emphasis is mine.

References

1. Bassett AS, Chow EWC, Husted J, et al. Clinical features of 78 adults with 22q11 deletion syndrome. Am J Med Genet A 2005;138:307-13. [Medline]
2. Bassett AS, Chow EWC. 22q11 deletion syndrome: a genetic subtype of schizophrenia. Biol Psychiatry 1999;46:882-91. [Medline]