Uniparental disomy
Encyclopedia
Uniparental disomy occurs when a person receives two copies of a chromosome
, or part of a chromosome, from one parent and no copies from the other parent.. UPD could involve isodisomy (meiosis II error) or heterodisomy (meiosis I error) .
or sperm
cells or may happen in early fetal
development. It can also occur during trisomic rescue
.
II, the genotype
may include identical copies of the uniparental chromosome (isodisomy), leading to the manifestation of rare recessive
disorders. UPD should be suspected in an individual manifesting a recessive disorder, where only one parent is a carrier
.
Uniparental inheritance of imprinted
genes can also result in phenotypical anomalies. Few imprinted genes have been identified, however uniparental inheritance of an imprinted gene can result in the loss of gene function which can lead to delayed development, mental retardation, or other medical problems.
2, 5-11, 13-16, 21 and 22.
This article incorporates public domain text from The U.S. National Library of Medicine
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
, or part of a chromosome, from one parent and no copies from the other parent.. UPD could involve isodisomy (meiosis II error) or heterodisomy (meiosis I error) .
Pathophysiology
UPD can occur as a random event during the formation of eggOvum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
or sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
cells or may happen in early fetal
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
development. It can also occur during trisomic rescue
Trisomic rescue
Trisomic rescue a genetic phenomenon in which a fertilized ovum containing three copies of a chromosome loses one of these chromosomes to form a normal, diploid chromosome complement. If both of the retained chromosomes came from the same parent, then uniparental disomy results....
.
- When the child receives two (different) homologous chromosomes (inherited from both grandparents) from one parent, this is called an heterodisomic UPD. Heterodisomy (heterozygous) indicates a meiosis I error.
- When the child receives two (identical) replica copies of a single homolog of a chromosomeChromosomeA chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
, this is called an isodisomic UPD. Isodisomy (homozygous) indicates either a meiosis II or postzygotic chromosomal duplication.
Phenotype
Most occurrences of UPD result in no phenotypical anomalies. However, if the UPD causing event happens during meiosisMeiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
II, the genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
may include identical copies of the uniparental chromosome (isodisomy), leading to the manifestation of rare recessive
Recessive
In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...
disorders. UPD should be suspected in an individual manifesting a recessive disorder, where only one parent is a carrier
Genetic carrier
A genetic carrier , is a person or other organism that has inherited a genetic trait or mutation, but who does not display that trait or show symptoms of the disease. They are, however, able to pass the gene onto their offspring, who may then express the gene...
.
Uniparental inheritance of imprinted
Imprinting (genetics)
Genomic imprinting is a genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner. It is an inheritance process independent of the classical Mendelian inheritance. Imprinted alleles are silenced such that the genes are either expressed only from the non-imprinted...
genes can also result in phenotypical anomalies. Few imprinted genes have been identified, however uniparental inheritance of an imprinted gene can result in the loss of gene function which can lead to delayed development, mental retardation, or other medical problems.
- The most well-known conditions include Prader-Willi syndromePrader-Willi syndromePrader–Willi syndrome is a rare genetic disorder in which seven genes on chromosome 15 are deleted or unexpressed on the paternal chromosome...
and Angelman syndromeAngelman syndromeAngelman syndrome is a neuro-genetic disorder characterized by intellectual and developmental delay, sleep disturbance, seizures, jerky movements , frequent laughter or smiling, and usually a happy demeanor....
. Both of these disorders can be caused by UPD or other errors in imprinting involving genes on the long arm of chromosome 15. - Other conditions, such as Beckwith-Wiedemann syndromeBeckwith-Wiedemann syndromeBeckwith–Wiedemann syndrome is an overgrowth disorder usually present at birth characterized by an increased risk of childhood cancer and certain congenital features. Originally, Dr...
, 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, mental retardationMental retardationMental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
and joint contractures among others.
All chromosomes
Occasionally, all chromosomes will be inherited from one parent, due to either a sperm fertilizing an empty egg and duplicating itself, or a diploid egg that is not fertilized. The effect is similar to triploidy, with either a molar pregnancy with no embryo if only paternal genes are present, or an embryo with no placenta if only maternal genes are present. Neither condition ever results in a liveborn infant.History
The first clinical case of UPD was reported in 1988 and involved a girl with cystic fibrosis and unusually 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 ChromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
2, 5-11, 13-16, 21 and 22.
External links
- Uniparental disomy (University of British Columbia)
This article incorporates public domain text from The U.S. National Library of Medicine