Diagnosis of 22q11.2 Deletion
Genetic testing to confirm the 22q11.2 deletion is usually done from a simple blood sample sent to a clinical lab. The recommended test today involves methods that are more sophisticated than the previously used fluorescence in situ hybridization (FISH) as the new tests also can tell the size of the deletion or duplication. These include “genome-wide” methods such as comparative genomic hybridization (CGH), a SNP microarray (e.g., CGA) or MLPA test. Again, targeted FISH studies can miss some smaller “nested” 22q11.2 deletions/duplications that the more sophisticated methods will detect. A standard cytogenetic test (karyotype) is only very rarely able to detect the 22q11.2 deletion in about 25% of cases and is therefore not a recommended method for detecting 22q11.2DS.
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Diagnosis of 22q11.2 Duplication
22q11.2 Duplication Syndrome is not detectable by routine genetic testing (called karyotyping.) Most individuals with 22q11.2 duplication are identified either by something called array genomic hybridization (array GH) testing or by multiplex ligation-dependent probe amplification (MLPA) testing for 22q11.2 deletion syndrome. Both of these tests are performed with blood work but can be diagnosed in pregnancy using cells from the placenta or the amniotic fluid.
The 22q11.2 deletion is most often not inherited from either parent and does not usually run in a family. Parents without the deletion are not at increased risk of having a second affected child. However, a person with the deletion has a 50% chance of passing it on to his or her child with every pregnancy. Only about 10% of children with the 22q11.2 deletion have a parent who is also affected. In the majority of individuals, the deletion happens sporadically without a previous family history of the condition. It is also important for parents to keep in mind that nothing they did or failed to do could have caused the deletion to occur. It is common for parents to initially feel a sense of guilt over the fact that their child has a “genetic condition,” but it is clear that this was out of their control and not anyone’s fault.