special subjects
DNA Variants and Mutations
Uniparental disomy
Uniparental disomy occurs when Both chromosomes have been inherited from only one parent It is very rare and is thought to involve trisomy rescue; ie, the zygote started off as a trisomy (having 3 instead of 2 of a particular chromosome) and one of the 3 was lost, a process that leads to uniparental disomy when the 2 chromosomes that remain are from the same parent (in about one third of cases). Uniparental disomy may cause abnormal phenotypes and inheritance patterns. For example, if duplicates of the same chromosome (isodisomy) are present and carry an abnormal allele for an autosomal recessive disorder, affected people can have an autosomal recessive disorder even though only one parent is a carrier. Uniparental disomy can result in an imprinting disorder when the disomic chromosome results in the loss of appropriate expression of a critically imprinted region (eg, Secondary hypogonadism may result from maternal isodisomy of chromosome 15). 