Chromosome 15q duplication is an extremely rare genetic disorder in which there is an excess copy of a segment of DNA found on the long ("q") arm of human chromosome 15. As a result, affected cells contain a total of 3 copies of the duplicated bases, instead of the usual 2 copies - one inherited from the mother and one from the father - found in a normal human diploid genome.
Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any number of complete chromosome sets is called a euploid cell.
Patau syndrome is a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. The extra genetic material disrupts normal development, causing multiple and complex organ defects.
Edwards syndrome, also known as trisomy 18, is a genetic disorder caused by the presence of a third copy of all or part of chromosome 18. Many parts of the body are affected. Babies are often born small and have heart defects. Other features include a small head, small jaw, clenched fists with overlapping fingers, and severe intellectual disability.
Mosaicism or genetic mosaicism is a condition in multicellular organisms in which a single organism possesses more than one genetic line as the result of genetic mutation. This means that various genetic lines resulted from a single fertilized egg. Mosaicism is one of several possible causes of chimerism, wherein a single organism is composed of cells with more than one distinct genotype.
Robertsonian translocation (ROB) is a chromosomal abnormality wherein a certain type of a chromosome becomes attached to another. 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 health difficulties, but can in some cases result in genetic disorders such as Down syndrome and Patau syndrome. Robertsonian translocations result in a reduction in the number of chromosomes.
Cri du chat syndrome is a rare genetic disorder due to a partial chromosome deletion on chromosome 5. Its name is a French term referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births across all ethnicities and is more common in females by a 4:3 ratio.
A small supernumerary marker chromosome (sSMC) is an abnormal extra chromosome. It contains copies of parts of one or more normal chromosomes and like normal chromosomes is located in the cell's nucleus, is replicated and distributed into each daughter cell during cell division, and typically has genes which may be expressed. However, it may also be active in causing birth defects and neoplasms. The sSMC's small size makes it virtually undetectable using classical cytogenetic methods: the far larger DNA and gene content of the cell's normal chromosomes obscures those of the sSMC. Newer molecular techniques such as fluorescence in situ hybridization, next generation sequencing, comparative genomic hybridization, and highly specialized cytogenetic G banding analyses are required to study it. Using these methods, the DNA sequences and genes in sSMCs are identified and help define as well as explain any effect(s) it may have on individuals.
Trisomy 8 causes Warkany syndrome 2, a human chromosomal disorder caused by having three copies (trisomy) of chromosome 8. It can appear with or without mosaicism.
Polysomy is a condition found in many species, including fungi, plants, insects, and mammals, in which an organism has at least one more chromosome than normal, i.e., there may be three or more copies of the chromosome rather than the expected two copies. Most eukaryotic species are diploid, meaning they have two sets of chromosomes, whereas prokaryotes are haploid, containing a single chromosome in each cell. Aneuploids possess chromosome numbers that are not exact multiples of the haploid number and polysomy is a type of aneuploidy. A karyotype is the set of chromosomes in an organism and the suffix -somy is used to name aneuploid karyotypes. This is not to be confused with the suffix -ploidy, referring to the number of complete sets of chromosomes.
Monosomy 9p is a rare chromosomal disorder in which some DNA is missing or has been deleted on the short arm region, “p”, of one of the 9th Chromosomes (9p22.2-p23). This deletion either happens de novo or a result of a parent having the chromosome abnormality. This rare chromosome abnormality is often diagnosed after birth when development delay, irregular facial features, and structural irregularities within the heart, and genital defects are noticed. Treatments for this syndrome usually focus on fixing the common malformations associated with this syndrome. Chromosome 9p deletion syndrome was first discovered in 1973 when 3 infants with similar clinical features were observed to have a partial deletion of the short arm of Chromosome 9. Symptoms include microgenitalia, intellectual disability with microcephaly and dysmorphic features.
The Pallister–Killian syndrome (PKS), also termed tetrasomy 12p mosaicism or the Pallister mosaic aneuploidy syndrome, is an extremely rare and severe genetic disorder. PKS is due to the presence of an extra and abnormal chromosome termed a small supernumerary marker chromosome (sSMC). sSMCs contain copies of genetic material from parts of virtually any other chromosome and, depending on the genetic material they carry, can cause various genetic disorders and neoplasms. The sSMC in PKS consists of multiple copies of the short arm of chromosome 12. Consequently, the multiple copies of the genetic material in the sSMC plus the two copies of this genetic material in the two normal chromosome 12's are overexpressed and thereby cause the syndrome. Due to a form of genetic mosaicism, however, individuals with PKS differ in the tissue distributions of their sSMC and therefore show different syndrome-related birth defects and disease severities. For example, individuals with the sSMC in their heart tissue are likely to have cardiac structural abnormalities while those without this sSMC localization have a structurally normal heart.
Ring chromosome 20, ring-shaped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms of chromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures, behaviour disorders and intellectual disability.
Cat eye syndrome (CES) or Schmid–Fraccaro syndrome is a rare condition caused by an abnormal extra chromosome, i.e. a small supernumerary marker chromosome. This chromosome consists of the entire short arm and a small section of the long arm of chromosome 22. In consequence, individuals with the cat eye syndrome have three (trisomic) or four (tetrasomic) copies of the genetic material contained in the abnormal chromosome instead of the normal two copies. The prognosis for patients with CES varies depending on the severity of the condition and their associated signs and symptoms, especially when heart or kidney abnormalities are seen.
Trisomy 22 is a chromosomal disorder in which three copies of chromosome 22 are present rather than two. It is a frequent cause of spontaneous abortion during the first trimester of pregnancy. Progression to the second trimester and live birth are rare. This disorder is found in individuals with an extra copy or a variation of chromosome 22 in some or all cells of their bodies.
Trisomy 16 is a chromosomal abnormality in which there are 3 copies of chromosome 16 rather than two. It is the most common trisomy leading to miscarriage and the second most common chromosomal cause of it, closely following X-chromosome monosomy. About 6% of miscarriages have trisomy 16. Those mostly occur between 8 and 15 weeks after the last menstrual period.
Tetrasomy 9p is a rare chromosomal disorder characterized by the presence of two extra copies of the short arm of chromosome 9, in addition to the usual two. Symptoms of tetrasomy 9p vary widely among affected individuals but typically include varying degrees of delayed growth, abnormal facial features and intellectual disability. Symptoms of the disorder are comparable to those of trisomy 9p.
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.
Pentasomy X, also known as 49,XXXXX, is a chromosomal disorder in which a female has five, rather than two, copies of the X chromosome. Pentasomy X is associated with short stature, intellectual disability, characteristic facial features, heart defects, skeletal anomalies, and pubertal and reproductive abnormalities. The condition is exceptionally rare, with an estimated prevalence between 1 in 85,000 and 1 in 250,000.
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 it is rarely diagnosed; fewer than 10% of those with the condition know they have it.
