<unk> .2<unk>  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<unk>  deletion syndrome have a 50/50 chance of passing it to their children. De novo<unk> .2<unk>  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.
22q11.2 distal deletion syndrome
13q deletion syndrome
22q13 deletion syndrome
2q37 deletion syndrome
1q21.1 deletion syndrome
9q34 deletion syndrome
1p36 deletion syndrome
Chromosome 5q deletion syndrome