<unk>  is a<unk>  caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. The extra genetic material disrupts normal development, causing multiple and complex organ defects. This can occur either because each cell contains a full extra copy of chromosome 13 (a disorder known as trisomy 13 or trisomy D or T13), or because each cell contains an extra partial copy of the chromosome or because there are two different lines of cells - one healthy with the correct number of chromosomes 13 and one that contains an extra copy of the chromosome- mosaic<unk> . Full trisomy 13 is caused by nondisjunction of chromosomes during meiosis (the mosaic form is caused by nondisjunction during mitosis). Like all nondisjunction conditions (such as Down<unk>  and Edwards<unk> , the risk of this<unk>  in the offspring increases with maternal age at pregnancy, with about 31 years being the average.<unk>  affects somewhere between 1 in 10,000 and 1 in 21,700 live births.
Patau syndrome
Bart syndrome
McGillivray syndrome
Sotos syndrome
Keutel syndrome
Cortes Lacassie syndrome
Bart–Pumphrey syndrome
Fryns-Aftimos syndrome