Бір аталық дизомия: себептері, түрлері және клиникалық маңызы

Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or of part of a chromosome, from one parent and no copy from the other. UPD can be the result of heterodisomy, in which a pair of non identical chromosomes are inherited from one parent (an earlier stage meiosis I error) or isodisomy, in which a single chromosome from one parent is duplicated (a later stage meiosis II error). Uniparental disomy may have clinical relevance for several reasons. For example, either isodisomy or heterodisomy can disrupt parent specific genomic imprinting, resulting in imprinting disorders. Additionally, isodisomy leads to large blocks of homozygosity, which may lead to the uncovering of recessive genes, a similar phenomenon seen in inbred children of consanguineous partners. UPD has been found to occur in about 1 in 2,000 births.

UPD can occur as a random event during the formation of egg cells or sperm cells or may happen in early fetal development. It can also occur during trisomic rescue. When the child receives two (different) homologous chromosomes (inherited from both grandparents) from one parent, this is called heterodisomic UPD. Heterodisomy (heterozygous) indicates a meiosis I error if the gene loci in question didn't cross over. When the child receives two (identical) replica copies of a single homologue of a chromosome, this is called an isodisomic UPD. Isodisomy (homozygous) indicates either a meiosis II (if the gene loci in question didn't cross over
Other conditions, such as Beckwith–Wiedemann syndrome, are associated with abnormalities of imprinted genes on the short arm of chromosome 11. Chromosome 14 is also known to cause particular symptoms such as skeletal abnormalities, intellectual disability, and joint contractures, among others. UPD has rarely been studied prospectively, with most reports focusing on either known conditions or incidental findings. It has been proposed that the incidence may not be as low as believed, rather it may be under reported.

Genome wide UPD, also called uniparental diploidy, is when all chromosomes are inherited from one parent. Only in mosaic form can this phenomenon be compatible with life. As of 2017, there have only been 18 reported cases of genome wide UPD.

Eric Engel first proposed the concept of uniparental disomy in 1980 as both homologous chromosomes are inherited from one parent, with no contribution (for that chromosome) from the other parent. Eight years later in 1988, the first clinical case of UPD was reported and involved a girl with cystic fibrosis and short stature who carried two copies of maternal chromosome 7. Since 1991, out of the 47 possible disomies, 29 have been identified among individuals ascertained for medical reasons. This includes chromosomes 2, 5–11, 13–16, 21 and 22.