Genetic counseling is the process of providing individuals and families with information on the nature, inheritance, and implications of genetic disorders to help them make informed medical and personal decisions. The following section deals with genetic risk assessment and the use of family history and genetic testing to clarify genetic status for family members. This section is not meant to address all personal, cultural, or ethical issues that individuals may face or to substitute for consultation with a genetics professional. To find a genetics or prenatal diagnosis clinic, see the GeneTests Clinic Directory.
Mode of Inheritance
The 22q11.2 deletion syndrome is a contiguous deletion syndrome inherited in an autosomal dominant manner.
Risk to Family Members:
- About 93% of probands have a de novo deletion of 22q11.2.
- Seven percent have inherited the deletion from a parent.
- Recommendations for the evaluation of parents of a proband include FISH testing because mildly affected adults, as well as normal adults with somatic mosaicism, have been identified [McDonald-McGinn et al 2001].
- The risk to the sibs of a proband depends upon the status of the parents.
- If the parents of an individual with the 22q11.2 deletion syndrome have normal FISH studies, the risk to sibs is low, but greater than that of the general population because parents with germline mosaicism or low-level somatic mosaicism have been identified.
- If a parent is also found to have the 22q11.2 deletion syndrome, the risk to each sib is 50%.
Offspring of individuals with the 22q11.2 deletion syndrome have a 50% chance of inheriting deletion 22q11.2.
The risk to other family members depends upon the status of the proband’s parents. If a parent is found to have the deletion, his or her family members are at risk.
The optimal time for determination of genetic risk and discussion of the availability of prenatal testing is before pregnancy. Similarly, decisions about testing to determine the genetic status of at-risk asymptomatic family members are best made before pregnancy.
DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, mutations, and diseases will improve in the future, consideration should be given to banking DNA of affected individuals. See Image testing.jpg for a list of laboratories offering DNA banking.
High-risk pregnancies. Prenatal testing using FISH analysis is available.
- Chromosome preparations from fetal cells obtained by amniocentesis usually performed at approximately 15-18 weeks’ gestation or CVS at approximately ten to 12 weeks’ gestation can be analyzed using FISH in the same manner described in Molecular Genetic Testing.
- Fetuses at increased risk may be evaluated between 18 and 22 weeks’ gestation by high-resolution ultrasound examination for palatal and other associated anomalies and by echocardiography for cardiac anomalies.
Note: Gestational age is expressed as menstrual weeks calculated either from the first day of the last normal menstrual period or by ultrasound measurements.
In some fetuses not known by family history to be at increased risk for the 22q11.2 deletion syndrome, findings of congenital heart disease and/or cleft palate detected by routine ultrasound examination may suggest the diagnosis, in particular in those individuals with conotruncal cardiac anomalies such as interrupted aortic arch,truncusarteriosus, tetralogy of Fallot, and ventricular septal defect. Chromosome preparations obtained from fetal cells can be analyzed using FISH. Establishing the diagnosis of the 22q11.2 deletion syndrome even late in gestation can be useful for perinatal management.