22q11.2 distal deletion syndrome

22q11.2 distal deletion syndrome
Other names	Distal del(22)(q11.2)[1]
Schematic overview of the 22q11.2 deletion region [2]

22q11.2 distal deletion syndrome is a rare genetic condition caused by a tiny missing part of one of the body's 46 chromosomes –

The first published description of a person with a 22q11.2 distal deletion was in 1999.[4] There have since been hundreds of cases reported worldwide. 22q11.2 distal deletion syndrome seems to occur equally often in males and females. There are reports of people who are unaffected by carrying the deletion and only discovered it after their child was diagnosed. It seems that the 22q11.2 distal deletion can be "silent" and it is unknown how many people may have a silent form of this syndrome.

Presentation

Every 22q11.2 distal deletion is unique, and each person may have different medical and developmental concerns. A number of common features have emerged:^{[citation needed]}

• Some children are likely to need support with learning. The amount of support needed by each child will vary
• Speech is often delayed and some children have articulation problems
• Growth delay both in the womb and after birth
• Heart problems
• Behavioral difficulties such as difficulties with concentration and anxiety
• Subtly unusual facial features. Families may notice similarities between their own child and others with the deletion

Cause

22q11.2 distal deletion occurs spontaneously; there is no known environmental cause. The genetic term for this is de novo; both parents typically have normal chromosomes. This is hereditary and people affected by distal deletion syndrome have a 50/50 chance of passing it to their children.^{[citation needed]}

De novo 22q11.2 distal deletions are caused by a mistake that is thought to occur when the parents' sperm or egg cells are formed. At one point in the formation, all the chromosomes including the two chromosome 22s pair up and swap segments. To pair up precisely, each chromosome 'recognizes' matching or near-matching DNA sequences on its partner chromosome. However, throughout each chromosome there are many similar DNA sequences that can overlap incorrectly, and pair with the wrong sequence. It is believed that when the exchange of genetic material, known as 'crossing over', occurs after mismatching, it is unequal, looping out and excising a length of the chromosome.^{[citation needed]}

Diagnosis

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Treatment

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Research

The features of 22q11.2 distal deletion syndrome are likely to be the result of the loss of a number of different genes found in this region. Most people have an approximately 0.4 to 2.1 Mb deletion (400'000- 2. Millions bases). Although the gene(s) responsible for the clinical features associated with 22q11.2 distal deletion syndrome have not been clearly defined, several potential candidate genes have been suggested.^{[citation needed]}