Genomic imprinting is an epigenetic phenomenon that causes genes to be expressed or not, depending on whether they are inherited from the female or male parent. Genes can also be partially imprinted. Partial imprinting occurs when alleles from both parents are differently expressed rather than complete expression and complete suppression of one parent's allele. Forms of genomic imprinting have been demonstrated in fungi, plants and animals. In 2014, there were about 150 imprinted genes known in mice and about half that in humans. As of 2019, 260 imprinted genes have been reported in mice and 228 in humans.
Prader–Willi syndrome (PWS) is a rare genetic disorder caused by a loss of function of specific genes on chromosome 15. In newborns, symptoms include weak muscles, poor feeding, and slow development. Beginning in childhood, those affected become constantly hungry, which often leads to obesity and type 2 diabetes. Mild to moderate intellectual impairment and behavioral problems are also typical of the disorder. Often, affected individuals have a narrow forehead, small hands and feet, short height, and light skin and hair. Most are unable to have children.
Chromosome 15q partial deletion is a rare human genetic disorder, caused by a chromosomal aberration in which the long ("q") arm of one copy of chromosome 15 is deleted, or partially deleted. Like other chromosomal disorders, this increases the risk of birth defects, developmental delay and learning difficulties, however, the problems that can develop depend very much on what genetic material is missing. If the mother's copy of the chromosomal region 15q11-13 is deleted, Angelman syndrome (AS) can result. The sister syndrome Prader-Willi syndrome (PWS) can result if the father's copy of the chromosomal region 15q11-13 is deleted. The smallest observed region that can result in these syndromes when deleted is therefore called the PWS/AS critical region. In addition to deletions, uniparental disomy of chromosome 15 also gives rise to the same genetic disorders, indicating that genomic imprinting must occur in this region.
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 or isodisomy, in which a single chromosome from one parent is duplicated. 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.
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division (mitosis/meiosis). There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).
Robertsonian translocation (ROB) is a chromosomal abnormality where the entire long arms of two different chromosomes become fused to each other. It is the most common form of chromosomal translocation in humans, affecting 1 out of every 1,000 babies born. It does not usually cause medical problems, though some people may produce gametes with an incorrect number of chromosomes, resulting in a risk of miscarriage. In rare cases this translocation results in Down syndrome and Patau syndrome. Robertsonian translocations result in a reduction in the number of chromosomes. A Robertsonian evolutionary fusion, which may have occurred in the common ancestor of humans and other great apes, is the reason humans have 46 chromosomes while all other primates have 48. Detailed DNA studies of chimpanzee, orangutan, gorilla and bonobo apes has determined that where human chromosome 2 is present in our DNA in all four great apes this is split into two separate chromosomes typically numbered 2a and 2b. Similarly, the fact that horses have 64 chromosomes and donkeys 62, and that they can still have common, albeit usually infertile, offspring, may be due to a Robertsonian evolutionary fusion at some point in the descent of today's donkeys from their common ancestor.
Chromosome 15 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 15 spans about 99.7 million base pairs and represents between 3% and 3.5% of the total DNA in cells. Chromosome 15 is an acrocentric chromosome, with a very small short arm, which contains few protein coding genes among its 19 million base pairs. It has a larger long arm that is gene rich, spanning about 83 million base pairs.
A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where there is an atypical number of chromosomes, or as structural abnormalities, where one or more individual chromosomes are altered. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. Chromosome abnormalities may be detected or confirmed by comparing an individual's karyotype, or full set of chromosomes, to a typical karyotype for the species via genetic testing.
Confined placental mosaicism (CPM) represents a discrepancy between the chromosomal makeup of the cells in the placenta and the cells in the fetus. CPM was first described by Kalousek and Dill in 1983. CPM is diagnosed when some trisomic cells are detected on chorionic villus sampling and only normal cells are found on a subsequent prenatal test, such as amniocentesis or fetal blood sampling. In theory, CPM is when the trisomic cells are found only in the placenta. CPM is detected in approximately 1-2% of ongoing pregnancies that are studied by chorionic villus sampling (CVS) at 10 to 12 weeks of pregnancy. Chorionic villus sampling is a prenatal procedure which involves a placental biopsy. Most commonly when CPM is found it represents a trisomic cell line in the placenta and a normal diploid chromosome complement in the baby. However, the fetus is involved in about 10% of cases.
Trisomic rescue is a genetic phenomenon in which a fertilized ovum containing three copies of a chromosome loses one of these chromosomes to form a diploid chromosome complement. If both of the retained chromosomes come from the same parent, then uniparental disomy results. If the retained chromosomes come from different parents then there are no phenotypic or genotypic anomalies. The mechanism of trisomic rescue has been well confirmed in vivo, and alternative mechanisms that occur in trisomies are rare in comparison.
KCNQ1 overlapping transcript 1, also known as KCNQ1OT1, is a long non-coding RNA gene found in the KCNQ1 locus. This locus consists of 8–10 protein-coding genes, specifically expressed from the maternal allele, and the paternally expressed non-coding RNA gene KCNQ1OT1. KCNQ1OT1 and KCNQ1 are imprinted genes and are part of an imprinting control region (ICR). Mitsuya identified that KCNQ1OT1 is an antisense transcript of KCNQ1. KCNQ1OT1 is a paternally expressed allele and KCNQ1 is a maternally expressed allele. KCNQ1OT1 is a nuclear, 91 kb transcript, found in close proximity to the nucleolus in certain cell types.
18p-, also known as monosomy 18p, deletion 18p syndrome, del(18p) syndrome, partial monosomy 18p, or de Grouchy syndrome 1, is a genetic condition caused by a deletion of all or part of the short arm of chromosome 18. It occurs in about 1 of every 50,000 births.
Neonatal diabetes mellitus (NDM) is a disease that affects an infant and their body's ability to produce or use insulin. NDM is a kind of diabetes that is monogenic and arises in the first 6 months of life. Infants do not produce enough insulin, leading to an increase in glucose accumulation. It is a rare disease, occurring in only one in 100,000 to 500,000 live births. NDM can be mistaken for the much more common type 1 diabetes, but type 1 diabetes usually occurs later than the first 6 months of life. There are two types of NDM: permanent neonatal diabetes mellitus (PNDM), a lifelong condition, and transient neonatal diabetes mellitus (TNDM), a form of diabetes that disappears during the infant stage but may reappear later in life.
Silver–Russell syndrome, also called Silver–Russell dwarfism, is a rare congenital growth disorder. In the United States it is usually referred to as Russell–Silver syndrome, and Silver–Russell syndrome elsewhere. It is one of 200 types of dwarfism and one of five types of primordial dwarfism.
The imprinted brain hypothesis is an unsubstantiated hypothesis in evolutionary psychology regarding the causes of autism spectrum and schizophrenia spectrum disorders, first presented by Bernard Crespi and Christopher Badcock in 2008. It claims that certain autistic and schizotypal traits are opposites, and that this implies the etiology of the two conditions must be at odds.
Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. Chromosomal deletion syndromes typically involve larger deletions that are visible using karyotyping techniques. Smaller deletions result in Microdeletion syndrome, which are detected using fluorescence in situ hybridization (FISH)
Isodisomy is a form of uniparental disomy in which both copies of a chromosome, or parts of it, are inherited from the same parent. It differs from heterodisomy in that instead of a complete pair of homologous chromosomes, the fertilized ovum contains two identical copies of a single parental chromosome. This may result in the expression of recessive traits in the offspring. Some authors use the term uniparental disomy and isodisomy interchangeably.
Tetrasomy X, also known as 48,XXXX, is a chromosomal disorder in which a female has four, rather than two, copies of the X chromosome. It is associated with intellectual disability of varying severity, characteristic "coarse" facial features, heart defects, and skeletal anomalies such as increased height, clinodactyly, and radioulnar synostosis. Tetrasomy X is a rare condition, with few medically recognized cases; it is estimated to occur in approximately 1 in 50,000 females.
Trisomy X, also known as triple X syndrome and characterized by the karyotype 47,XXX, is a chromosome disorder in which a female has an extra copy of the X chromosome. It is relatively common and occurs in 1 in 1,000 females, but is rarely diagnosed; fewer than 10% of those with the condition know they have it.
Kagami-Ogata syndrome is a rare genetic disease that is caused by mutations on Maternal chromosome 14 or by paternal UPD(14). The main signs of this disease are: polyhydramnios, narrow bell-shaped thorax, coat-hanger-like ribs, abdominal wall defect, enlarged placenta. Patients with KOS also have a facial dysmorphism, such as: frontal bossing, excessive hair growth on forehead, depressed nasal bridge, micrognathia with/or retrognathia, full cheeks, webbed neck, protruding philtrum.
