FAQs - Section 2: Chromosome Deletions in Pregnancy
A chromosome deletion is the absence of a segment of the DNA from a chromosome. The overall number of chromosomes is normal, but one chromosome is missing some of its DNA. A deletion is often referred to as a ‘microdeletion’ as the segment may be extremely small.
22q11.2 deletion syndrome is a chromosomal condition that occurs when there is a small deletion in a specific region of chromosome 22. This deletion is so small it is usually undetectable when using conventional screening methods. This deletion results in the absence of a number of genes, which are responsible for the clinical features described below.
22q11.2 deletion is the most common chromosomal microdeletion.
- This condition may occur in as many as one in 1,000 pregnancies.
- After Down syndrome (trisomy 21), it is the second most common cause of developmental delay with major congenital heart disease.
- It is more common than many other genetic conditions, such as cystic fibrosis.
- More than 90% of affected individuals have no family history of 22q11.2 deletion.
- 22q11.2 deletion is not reliably detected by routine screening or chromosome studies.
- Unlike some other chromosomal conditions, the chance of having a baby with 22q11.2 deletion syndrome does not increases with maternal age; it can occur in any pregnancy.
- Some patients may carry the 22q11.2 deletion themselves, or have a family history of the 22q11.2 deletion. NIPT is not possible for these patients, and the possibility of diagnostic testing (CVS or amniocentesis) should be considered, in conjunction with an appropriate specialist.
The early identification of 22q11.2 deletion in the developing baby will alter the management of a pregnancy. If this deletion is identified, the following actions should be considered:
- Genetic testing by CVS or amniocentesis to confirm the presence of the deletion.
- Detailed ultrasound with fetal echocardiogram to evaluate for anomalies, such as congenital heart defect, cleft palate, etc.
- Genetic counselling regarding the potential of other family members having the deletion.
- Specialist advice regarding documented or potential features of the 22q11.2 syndrome.
- Delivery at a tertiary care hospital.
The 22q11.2 deletion is the underlying cause of conditions described as DiGeorge syndrome and velocardiofacial syndrome. These conditions demonstrate a wide variety of features that vary in severity and age of onset. It is usually difficult to make an accurate prenatal prediction of the outcome for an individual.
There is an increased risk of psychiatric illness in later life
The clinical findings in a person with 22q11.2 deletion will vary with age. Some features of the syndrome will be evident at birth, e.g. abnormalities of the heart and palate. Other features may become evident in the first few months of life, e.g. swallowing difficulties. It may take a number of years for features such as delayed growth or development to be recognised.
The severity of 22q11.2 syndrome varies widely. Some people are severely affected, while others are very mildly affected. The 22q11.2 deletion may be present in a number of members of a family and, for reasons that are unknown, the severity can still vary widely. The diagnosis of 22q11.2 in a parent may only be made after the diagnosis has been made in a more severely affected child.