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The possession of a third chromosome of any one type in an otherwise diploid cell.

Year introduced: 1964(1963)


Trisomy 18 Syndrome

A chromosome disorder associated with TRISOMY of all or part of CHROMOSOME 18. Clinical manifestations include INTRAUTERINE GROWTH RETARDATION; CLEFT PALATE; CONGENITAL HEART DEFECTS; MICROCEPHALY; MICROGNATHIA and clenched fists with overlapping fingers. Most affected fetuses do not survive to birth. Those who survive through their first year often have severe INTELLECTUAL DISABILITY.

Year introduced: 2018


Trisomy 13 Syndrome

A chromosome disorder associated with TRISOMY of all or part of CHROMOSOME 13. Clinical manifestations include CONGENITAL HEART DEFECTS (e.g., PATENT DUCTUS ARTERIOSUS), facial malformations (e.g., CLEFT LIP; CLEFT PALATE; COLOBOMA; MICROPHTHALMIA); HYPOTONIA, digit malformations (e.g., POLYDACTYLY or SYNDACTYLY), and SEIZURES and severe INTELLECTUAL DISABILITY associated with NERVOUS SYSTEM MALFORMATIONS.

Year introduced: 2018(2010)


Down Syndrome

A chromosome disorder associated either with an extra CHROMOSOME 21 or an effective TRISOMY for chromosome 21. Clinical manifestations include HYPOTONIA, short stature, BRACHYCEPHALY, upslanting palpebral fissures, epicanthus, Brushfield spots on the iris, protruding tongue, small ears, short, broad hands, fifth finger clinodactyly, single transverse palmar crease, and moderate to severe INTELLECTUAL DISABILITY. Cardiac and gastrointestinal malformations, a marked increase in the incidence of LEUKEMIA, and the early onset of ALZHEIMER DISEASE are also associated with this condition. Pathologic features include the development of NEUROFIBRILLARY TANGLES in neurons and the deposition of AMYLOID BETA-PROTEIN, similar to the pathology of ALZHEIMER DISEASE. (Menkes, Textbook of Child Neurology, 5th ed, p213)

Year introduced: 1993


6q+ Syndrome, Partial [Supplementary Concept]

Date introduced: June 25, 2010


Chromosome 17 trisomy [Supplementary Concept]

Duplication of chromosome 17 in some tissues (trisomy 17 mosaicism) is among the rarest trisomy in humans and full trisomy 17 has never been observed in living individuals. In mosaic cases, where trisomy occurs only in some cell populations, affected individuals may experience developmental delays, body asymmetry, slow growth, and cerebellar hypoplasia.

Date introduced: August 25, 2010


Chromosome 16, trisomy [Supplementary Concept]

A chromosomal abnormality characterized by a third copy of chromosome 16. Full trisomy 16 is lethal in utero and is the most common chromosomal trisomy that results in miscarriage. Mosaic trisomy 16, where affected individuals carry an extra chromosome 16 only in some tissues, may result in intrauterine growth retardation and congenital heart defects.

Date introduced: August 25, 2010


Chromosome 5, trisomy 5p [Supplementary Concept]

Date introduced: August 25, 2010


Chromosome 20, trisomy [Supplementary Concept]

Date introduced: August 25, 2010


Klinefelter Syndrome

A form of male HYPOGONADISM, characterized by the presence of an extra X CHROMOSOME, small TESTES, seminiferous tubule dysgenesis, elevated levels of GONADOTROPINS, low serum TESTOSTERONE, underdeveloped secondary sex characteristics, and male infertility (INFERTILITY, MALE). Patients tend to have long legs and a slim, tall stature. GYNECOMASTIA is present in many of the patients. The classic form has the karyotype 47,XXY. Several karyotype variants include 48,XXYY; 48,XXXY; 49,XXXXY, and mosaic patterns ( 46,XY/47,XXY; 47,XXY/48,XXXY, etc.).

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