Abnormalities of chromosome 13 are usually most commonly associated with trisomy 13 and are the second most common autosomal disorder. It is more common in females than in males, and the incidence increases with the age of the pregnant mother. The main features are severe mental retardation, peculiar facial features, malformations of the hands and feet, and genitalia, accompanied by severe lethal malformations, with 90% of deaths occurring within the first year of life. Cytogenetics is characterized by trisomy of chromosome 13, which occurs mainly due to nondisjunction of chromosome 13 in the germ cells of one of the parents during meiosis to form gametes, or during mitosis of a fertilized egg, resulting in the memory of an extra chromosome 13 in the somatic cells of the embryo, and for which there is currently no effective treatment.