American College of Medical Genetics Statement on Diagnostic Testing for Uniparental Disomy

Uniparental disomy represents a departure from the usual situation in which one member of each pair of chromosomes (called homologous chromosomes) is normally inherited from each parent. Thus, for each of the 23 pairs of human chromosomes, one is normally inherited from the father and the other from the mother. Uniparental disomy (UPD) is the abnormal situation in which both members of a chromosome pair are inherited from one parent, and the other parent’s chromosome for that pair is missing.1 Uniparental disomy for some chromosomes is without consequence, but for a few chromosomes can result in abnormality in the affected individual through parent-of-origin differences in gene expression. Serious conditions, including syndromes affecting growth and development, can be the result. Below is an explanation of the mechanisms and consequences of UPD and recommendations for situations in which testing for UPD is indicated.