chromosome have a child with es, with male and female carriers having 0.7% and 3.4%, respectively, chances of parenting such a child. the afflicted children of these parents have an es-producing ssmc containing only part of their parents derivative chromosome. this ssmc is termed derivative 22, der(22) or der(22)t(11;22); the afflicted individuals' karyotypes (i.e. chromosome tallies) are 47,xx,+der(22)t(11;22) for females and 47,xy,+der(22)t(11;22) for males. the ssmc in es forms as a result of a nondisjunction, i.e. failure, of the parent's derivative chromosome to separate from its homolog, i.e. paired, chromosome properly during the meiotic cell divisions that form their sperms or eggs. the genetic material in ssmc der(22)t(11;22) that produces the defects in es has not been established. der(22)t(8;22)(q24.1;q11.1) syndrome der(22)t(8;22)(q24.1;q11.1) syndrome, also termed the supernumerary der(22)t(8;22) syndrome, is a syndrome in which individuals are born with normal birth weight and growth but have moderate mental retardation; dysmorphic features in the face and head areas; prominent, low-set, underdeveloped ear canals, and/or preauricular pits (small holes or cysts in front and above the ear canal); clinodactyly (abnormal curvature of one or more fingers and/or toes); and ectopic testis (testes in unusual locations) or cryptorchidism (undescended testes). this syndrome is associated with a ssmc derived from an abnormal chromosome carried by a parent. this chromosome contains a balanced translocation between the q arm around band 24.13 of chromosome 8 and the q arm around band 11.1 of chromosome 22. carriers of it are at risk of having progeny with the der(22)t(8;22)(q24.1;q11.1) syndrome because they acquired a ssmc that has alteration(s) in the parent's abnormal chromosome. this alteration occurs in the parent's egg or sperm as a result of an nondisjunction of the parent's paired t(8;22)chromosomes during the meiosis cell divisions that form the sperm or egg. the genetic material in this ssmc that causes this syndrome's defects has not been established. tetrasomy 9p tetrasomy 9p (also termed 9p isochromosome) is associated with a wide range of birth defects including intrauterine growth retardation; facial dysmorphism; cleft lip and/or palate; malformations of the limbs and skeleton; and/or abnormalities of the central nervous system, heart, and/or genitourinary tract. the ssmc in tetrasomy 9 cases is an isochromosome of one of 3 compositions: a) two p arms of chromosome 9 which are mirror images of each other; b) this chromosome's two p arms plus a small part of its q arm from bands 12 to 13; or c) this chromosomes two p arms plus a part of its q arm from bands 21 to 22. all three of these ssmc variant types contain two copies of the p arm genetic material that they contain and therefore render cells tetrasomeic, i.e. possessing 4 copies, of some of this arm's genetic material. however, there is a trisomy 9p-related congenital disorder which has only 3 copies of this genetic material due an abnormal chromosome 12 containing duplicate copies rather than a single copy of some genetic material. these individuals have trisomy 9p; they have birth defects similar to, but less severe than, those in tetrasomy 9p. the genetic material in tetrasomy 9 and trisomy 9p that causes the birth defects is not known. findings that a) 7 adult cases of tetrasomy 9p were essentially normal and b) many of the genetically detailed cases of tetrasomy 9p have other chromosome abnormalities suggest that the role of the cited ssmcs in tetrasomy 9p requires further study. isochromosome i (5p) isochromosome i (5p) (also termed tetrasomy 5p) is a congenital disorder associated with a wide range of birth defects the most common of which are: developmental delay, hypotonia, short stature, seizures, congenital heart defects, ventriculomegaly (enlargement of the brain's lateral ventricles), shortened survival in the uterus or after birth, psychomotor retardation, facial disfigurements, and/or feeding and/or breathing difficulties. most cases of isochomosome i 5p are diagnosed in individuals aged 0 to 5 years or, in a few cases, in the uterus. a 2018 review of 15 postnatal cases that had genetic analyses found 4 were associated with amplifications due to mutations in chromosome 5's p arm and 8 were associated with ssmcs consisting of two partial copies of this arm. all 12 individuals had 2 extra copies of large areas in the p arm. however, the exact genetic material on the p arm contributing to the disorder were not established. individuals with only one extra partial copy of th 5p arm, i.e. who were trisomic, have similar but perhaps less severe defects than those with tetrasomy i (5p). there are large variations in the types of defects shown in individuals with isochromosome i (5p) ssmc due, at least in part, to genetic mosaicism, i.e. differences in the tissue and organ distribution of this ssmc. isochromosome 18p syndrome isochromosome 18p syndrome, also termed tetrasomy 18p, is a birth disorder associated with microcephaly (shorter than normal head), small kidneys, cryptorchidism, micropenis, hypospadias (i.e. the penis's urethral opening is mis-located), strabismus, feeding difficulties, neonatal jaundice, kyphosis (excessive convex curvature of the spine), scoliosis (sideways curve of the spine), recurrent otitis media, hearing loss, constipation, feeding problems, dysmorphic features, and/or moderately severe mental retardation. the ssmc in this syndrome is composed of two extra copies of the short arm of chromosome 18 developed in most cases during formation of a parent's egg or sperm or in the fertilized zygote although rare inherited cases of the intact ssmc have been reported. the specific genetic material on isochromosome 18p ssmc contributing to the development of the syndrome has generally not been assigned. however, a recent report on one individual with the syndrome revealed a ssmc of at least 15 mb extending from band 11.21 to ll.32 on the p arm of chromosome 18. recently, identical female twins, i.e. twins with essentially identical copies of their parent's chromosomes, were studied because one twin clearly had the isochromosome 18p syndrome while the other appeared completely normal. genetic analysis found evidence for the presence of isochromosome 18p's ssmc in almost all or all the cells isolated from the inner cheek, hair follicles, and skin fibroblasts of the afflicted twin while the normal twin had ≤5% of the cells in these samples positive for this ssmc. neither parent showed evidence of having the ssmc. thus, the normal twin appeared to have an extreme form of mosaicism in which the ssmc was present in too few tissue cells to cause the birth defects associated with the isochromosome 15p syndrome. extreme levels of ssmc mosaicism in this and possibly other ssmc-associated disorders can be well tolerated, not associated with birth defects, and more common than currently considered. pallister-killian syndrome pallister–killian syndrome (pks) is a congenital disorder that includes an extremely wide range of birth defects. the most common of these are facial dysmorphism, pigmentary skin anomalies, profound intellectual disability, hypotonia, and/or seizures; some of its less common defects include deafness, extra breast nipples, congenital diaphragmatic hernias, and/or focal areas of absent skin. pks is commonly caused by an ssmc that is an isochromosome consisting of two p arms of chromosome 12 but in less common cases four p arms of this chromosome. recent studies in two individuals with pks found the ssmc consisted of two small duplications from band 11 to the terminus of the p arm on chromosome 12. this area, termed the pks critical region, contains three genes, ing4, chd4, and mfap5 (also termed the magp2 gene), one or more of which is a candidate causer of the syndrome. turner syndrome turner syndrome is a condition in which females typically have only one x chromosome and either no y or only part of a y chromosome. these individuals exhibit a wide range of relatively mild to moderately severe birth defects including in all cases short stature; in most cases ovarian failure and infertility; and in less common cases bone anomalies, lymphoedema, deafness, and/or cardiovascular, thyroid and gastrointestinal disorders. a small percentage of turner syndrome individuals have ssmcs that contain parts of the genetic material from an x or, much less frequently, y chromosome. these ssmcs may or may not contain an xist gene. in normal females, the xist gene occurs on the x chromosome inherited from her mother but not on the x chromosome inherited from her father. the gene is not present on y chromosomes and in normal females resides on and functions to inactivate many of the genes located on its own maternal but not the father's x chromosome. turner syndrome females with an ssmc consisting of a partial x chromosome that does not contain the xist gene express at least some of this ssmc's genetic material and therefore contain excesses of this material. in consequence, they have a more serious form of the turner syndrome that ranges form moderately severe to extremely severe. the extremely severe cases have anencephaly (absence of a major portion of the brain, skull, and scalp), agenesis of the corpus callosum (lack of the thick tract of nerve fibers that connect the left and right cerebral hemispheres), and complex heart deformities. individuals with turner syndrome that have partial x chromosome containing-ssmcs that have the xist gene do not express this ssmc's genetic material and do not suffer the cited severer manifestations of the syndrome. ssmc-associated infertility infertility as used here occurs in individuals who have no other overt birth defects. as such, it is diagnosed three times more often in individuals possessing ssmcs and occurs in 0.125% of all infertility cases. infertile men cannot impregnate, have abnormally low rates of impregnation, and/or impregnate their partner but their impregnations have abnormally high rates of spontaneous abortion. a review published in 2015 reported that the ssmc's in infertile men contain parts of any chromosome except chromosomes 10, 19, and x, with chromosomes 15, 14, 22, and 13/21 (i.e. a complex ssmc consisting of parts of chromosomes 13 and 21) being the most common. clinically, these men have either azoospermia (i.e. absence of sperm), oligozoospermia (i.e. abnormally low sperm counts), or aoligoasthenoteratozoospermia (i.e. all three of the following, oligozoospermia, teratozoospermia , and asthenozoospermia ). infertility associated with a ssmc in women is ~7.5-fold less common than in men but, like men, their ssmc's consist of almost any chromosome but particularly chromosomes 15, 14, 22, and 13/21. clinically, women with ssmc-associated infertility have a history of amenorrhea and/or primary ovarian insufficiency, i.e. premature menopause or symptoms related to premenopausal events such as partial or total losses of estrogens, progesterone, androstenedione, activin, and/or inhibin production by the ovaries before age 40. while only a small percentage of the chromosome areas involved in infertility due to ssmc's have been defined, those that have include: (15)q11.1, associated with premature ovarian failure; (13)q11.2, associated with oligoasthenoteratozoospermia; (14)q11.1, associated with infertility; and (22)q11, associated with repeated abortions. the specific genetic material producing infertility in these ssmcs has, in general, not been clearly defined. atypical lipomatous tumors atypical lipomatous tumors (alts) are a type of well-differentiated liposarcoma. the term alt is often applied to tumors located in surgically accessible locations such as the skin, oral cavity, or eye socket whereas the term well-differentiated liposarcomas is applied to tumors in less surgically accessible, deep, and centrally-located, soft tissues such as the retroperitoneum. here, the two terms are used interchangeably. unlike less well-differentiated liposarcomas which are malignant, alts, while sometimes locally invasive and recurring after surgical removal, do not metastasize and rarely progress to less differentiated and potentially metastasizing forms. they are therefore commonly regarded as benign or premalignant tumors. the neoplastic cells in alt contain one or more ring-shaped ssmcs or one giant marker chromosome (i.e. a chromosome enlarged by having a duplication of parts of its own or one or more other chromosomes) that contain extra copies of chromosome 12's q arm at bands 13 through 15. this stretch of chromosome 12 includes the mdm2 proto-oncogene (a potentially tumor-causing gene) located at band 15 and cdk4 (a gene associated with the development of various tumors) located at band 14.1. the presence of these two genes is a highly sensitive and specific indicator that a lipomatous tumor is an alt rather than another type of lipomatous tumor. the ssmcs and giant marker chromosomes involved in alt may contain sequences from other chromosomes; furthermore, the ring ssmcs frequently break, reseal, transform into a rod-shape, and develop gains and/or losses in their genetic material. these factors