Chromosome 22q11.2 duplication syndrome

22q11.2 duplication syndrome is inherited in families in what is known as an autosomal dominant manner. In human cells, chromosomes are arranged in 23 pairs of 2. The first 22 pairs of chromosomes are called autosomes and are numbered 1-22, while the 23rd pair is known as the sex chromosomes and determines gender (XX for female and XY for male). Individuals with 22q11.2 duplication typically have this duplication on one chromosome 22. A change on only one of the two chromosomes in a pair is sufficient to cause symptoms of 22q11.2 duplication in affected individuals (referred to as dominant inheritance).

If an individual has the 22q11.2 duplication on one chromosome 22, then with each pregnancy there is a 1 in 2 (50%) chance of passing on the duplicated chromosome 22, therefore, children of an individual with 22q11.2 duplication syndrome have a 50% chance of either inheriting or not inheriting the duplication from their affected parent, regardless of the gender of either the affected parent or the child.

About 70 percent of individuals with 22q11.2 duplication syndrome inherit the duplication from a parent who also has a duplication 22q11.2. In the remaining approximately 30% of individuals with 22q11.2 duplication syndrome, neither of the parents have a duplication on their 22nd chromosomes. This is referred to as a de novo (new) change, which occurred as a spontaneous event in either the egg or sperm at conception.

When a 22q11.2 duplication has occurred de novo (for the first time in an affected individual), the chance of the unaffected parents having a subsequent affected child in future pregnancies is estimated to be less than 1%. There is a small possibility that a parent havimay have a 22q11.2 duplication in only their egg or sperm cell, but not the cells in the rest of their body (this is known as gonadal mosaicism), and if present, would raise the chance of recurrence of 22q11.2 duplication in a subsequent pregnancy, even if the parent's chromosomes were normal when tested in the blood. Parents may also carry a different type of chromosome change other than the 22q11.2 duplication which raises the chances of 22q11.2 duplication or another chromosome change occurring in a pregnancy. Genetic testing on parents who have a child with 22q11.2 duplication is recommended.

When a 22q11.2 duplication occurs de novo in a pregnancy, there is nothing a parent can do to cause or reduce the chances of the 22q11.2 duplication in the child. No environmental, dietary, or lifestyle factors are known to cause this type of change in a chromosome.

When an individual has been diagnosed with 22q11.2 duplication syndrome, genetic testing and genetic counseling is an option for his or her parents and other family members who are concerned about the risk of recurrence of 22q11.2 duplication syndrome in other members of the family. The National Society of Genetic Counselors "Find a Genetic Counselor" search feature can locate a genetic counselor in the United States or Canada if a family is interested in genetic counseling regarding 22q11.2 duplication syndrome.