DiGeorge (22q11.2 Deletion) Syndrome

DiGeorge Syndrome (also known as 22q11.2 Deletion Syndrome, and formerly Velocardiofacial Syndrome) is a syndrome caused by the deletion of a small segment (microdeletion) of chromosome 22. It is the most common microdeletion syndrome in humans. This microdeletion is also responsible for a 20 to 30 times increased risk for schizophrenia, which equates to 1 in 4 individuals developing schizophrenia. Thus, 22q11.2 deletion is considered to be the first true molecular genetic subtype of schizophrenia. In addition, individuals often have congenital heart problems, facial dysmorphia, developmental delay, learning problems, and cleft palate. Renal impairment, hearing loss, infections, and autoimmune disorders are also common.

Epidemiology

The prevalence of 22q11.2 Deletion Syndrome is estimated to be between 1 in 2000-4000 births.

Risk Factors

90% of cases are usually new diagnoses with no identifiable family history. Genetically, there is variable expression of the deletion within families, and even between identical twins.

Epidemiology

DiGeorge syndrome has a prevalence of 1 in 4,000 people.[1] Individuals are also at a higher risk for early-onset Parkinson's Disease.

What the Heck Does 22q11.2 Mean?

The '22q11.2' in 22q11.2 Deletion Syndrome refers to (see figure 1):
  • 22: Chromosome 22
  • q: the long arm (“queue”) of the chromosome 22
    • All chromosomes have a short (“petite” or “p”) arm and a long (“queue” or “q”) arm
  • 11.2: the location on chromosome 22 (region (1), band (1), sub-band (2))

22q11.2 Deletion Fig. 1

The diagnosis of DiGeorge Syndrome can be confirmed with various methods of genetic testing, including whole genome array, SNP clinical microarray, comparative genomic hybridization, and Multiplex Ligation-dependent Probe Amplification (MLPA). Fluorescence In Situ Hybridization (FISH) studies can also find the deletion in most patients. Cytogenetic (chromosome) testing can also be performed.

A clinical microarray (CMA) is clinically recommended and a first-line test for any individual with intellectual disability, developmental delay and/or multiple congenital anomalies.[2][3] The diagnostic yield is around 10-20%. However, there are limitations in that it will not detect all genetic conditions.

The presentation of schizophrenia in individuals with DiGeorge Syndrome is indistinguishable from idiopathic forms of schizophrenia. There is a similar age of onset and prodromal symptoms. Therefore, current guidelines also recommend the same treatment, including with antipsychotics.[4] However, since these patients are at a baseline higher risk of obesity (even without antipsychotic use), there needs to be even more careful monitoring and prevention of metabolic side effects.[5] Individuals with DiGeorge syndrome and schizophrenia and typically under-recognized and not diagnosed. The estimated prevalence of schizophrenia patients having DiGeorge, is estimated to be 1 in 100-200 patients.[6]

Antipsychotics Can Mask Early-Onset Parkinson's Symptoms in DiGeorge + Schizophrenia Patients

Individuals with DiGeorge have a higher risk for early-onset Parkinson's Disease.[7] As a result, individuals with concomitant schizophrenia and on long-term antipsychotic treatment may have their emerging Parkinson's symptoms masked and mistakenly attributed as extrapyramidal symptoms.

The microdeletion in DiGeorge Syndrome is a new mutation (de novo) in almost 90% of cases.[8] There is a highly variable expression with incomplete penetrance.

  • Ionized calcium and PTH should be measured routinely (especially when there are major biological stressors such as a serious medical illness or surgery)[9]
  • TSH (annually)[10]

Patients with DiGeorge have complex needs and often require multidisciplinary teams. Clinical practice guidelines have recommended a various investigations and follow ups.[11][12]

Patients with DiGeorge respond to clozapine treatment as well those non-DiGeorge schizophrenia. However, they may represent an excess of serious adverse events, primarily seizures.[13] Lower doses and prophylactic seizure management strategies can help reduce this risk. Individuals are also at greater risk for neutropenia and myocarditis.

Patients should have daily Vitamin D and calcium supplementation.[14][15]