Chromosomal anomalies
- clinical conditions caused by an abnormal chromosome constitution in which there is extra or missing chromosome material, either a whole chromosome or a chromosome segment.
Down's syndrome
- A chromosomal abnormality consisting of the presence of a third copy of chromosome 21 in somatic cells.
- A disorder caused by the presence of an extra chromosome 21 and characterized by mental retardation and distinguishing physical features.
- 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, simian crease, and moderate to severe mental retardation.
- The most frequently occurring mental retardation/multiple anomaly syndrome usually involving more than 100 individual defects. Typical facies with upslanting palpebral fissures is the characteristic feature of this syndrome (hence the offensive designations "mongoloid idiocy" and "mongolism"). A wide range other defects, such as congenital heart diseases, respiratory disorders, and leukemia, may be associated. Down syndrome patients who survive into late adulthood may develop Alzheimer syndrome.
- A chromosomal dysgenesis syndrome resulting from a triplication or translocation of chromosome 21. Down syndrome occurs in approximately 1:700 live births. Abnormalities are variable from individual to individual and may include mental retardation, retarded growth, flat hypoplastic face with short nose, prominent epicanthic skin folds, small low-set ears with prominent antihelix, fissured and thickened tongue, laxness of joint ligaments, pelvic dysplasia, broad hands and feet, stubby fingers, transverse palmar crease, lenticular opacities and heart disease. Patients with Down syndrome have an estimated 10 to 30-fold increased risk for leukemia; most have symptoms of Alzheimer's disease by age 40. Also known as trisomy 21 syndrome. --2004
Patau's syndrome
- The presence of an additional (third) chromosome on an otherwise diploid chromosome 13 with variable abnormalities, most characteristic of which are microcephaly, microphthalmia, hypertelorism, cleft lip or palate, polydactyly, and cardiovascular, genitourinary, and neurological abnormalities. It is one of the most frequent causes of perinatal deaths.
Edwards' syndrome
- A syndrome characterized by the presence of an extra (third) chromosome on an otherwise diploid chromosome 18 associated with a broad spectrum of variable abnormalities consisting of more than 130 individual defects of the craniofacial structures, brain, heart, kidneys, and gut. One-third of newborn infants (weighing about 2300) are premature and two-thirds are female. Fetal abnormalities consist mainly of polyhydramnios, small placenta, and single umbilical artery. Tumors in some cases. Trisomy 18 mosaicism is often associated with normal intelligence and mild phenotype.
Autosomal deletion syndromes
Cri-du-chat syndrome
- infantile syndrome characterized by a cat-like cry, failure to thrive, microcephaly, mental retardation, spastic quadriparesis, micro- and retrognathia, glossoptosis, bilateral epicanthus, hypertelorism, and tiny external genitalia; caused by a deletion of the short arm of chromosome 5.
- Deletion of the short arm of chromosome 5 characterized by a variable clinical picture consisting of severe mental deficiency, growth retardation, multiple abnormalities and a peculiar crying sound resembling that of a suffering kitten (hence the synonym crying cat syndrome or cri du chat syndrome), that disappears within weeks or months after birth.
Velo-cardio-facial syndrome
- Typical facies with a prominent nose and retruded mandible, cleft palate, cardiovascular defects, learning disability, retarded mental development, and short stature. Elements of this syndrome are frequently present in the Robin syndrome.
- caused by microdeletion on chromosome 22q11.2; associated with multiple congenital anomalies, learning disabilities, behavioral phenotypes including ADHD and anxiety, with schizophrenic risk in adulthood.
Other microdeletions
- A developmental defect of the brain caused by incomplete neuronal migration and characterized by smoothness of the surface of the brain (lissencephaly) occurring in association with absence of the sulci and gyri (agyria) and thickening of the cerebral cortex with four rather than six layers (pachygyria), microcephaly, characteristic facial appearance, retarded growth and mental development, neurological complications, and multiple abnormalities of the brain, kidneys, heart, gastrointestinal tract, and other organs. Lissencephaly, once considered as synonymous with Walker-Warburg syndrome and Norman-Roberts syndrome, is now recognized as a component of several other syndromes. Type I (the classical form) is a component of Miller-Dieker and Norman-Roberts syndromes, also occurring as a separate entity; Type II the Walker-Warburg and muscle-eye-brain syndrome, also occurring in the Neu-Laxova syndrome.
- Deletion of the short arm of chromosome 17. As initially reported, the syndrome consisted mainly of cleft palate and congenital heart defect. The phenotype was later expanded to include brachycephaly, midfacial hypoplasia, broad nasal bridge, highly arched palate, mandibular prognathism, malformed ears, short hands, mental retardation, and other less constant abnormalities.
- a rare chromosomal disorder characterized by abnormalities of the craniofacial area (brachycephaly, prognathism, cleft palate), delays in the acquisition of skills requiring the coordination of mental and muscular activities, mental retardation; most affected individuals experience speech delays that may occur in association with hearing impairment; behavioral abnormalities may include hyperactivity and self-destructive behavior.
Other autosomal deletions
Balanced autosomal translocation in normal individual
Other conditions due to autosomal anomalies
Gonadal dysgenesis
- genetic disease that produces sterile females due to monosomy for X chromosome; the ovaries are rudimentary or missing; other abnormalities include short stature, webbed neck, and a broad chest with widely spaced nipples.
- A syndrome in which the affected patients have only 45 chromosomes, the loss of one of the X chromosomes producing an XO chromosome constitution. The syndrome occurs in 1/2500 female births and nearly 99% of XO fetuses are aborted. Gonadal agenesis and short stature are the main features in the surviving infants. Associated anomalies may included webbed neck, cubitus valgus, shield chest, short stature, lymphedema, coarctation of the aorta, pigmented nevi, and various renal, skeletal, dermatologic, neoplastic, and autoimmune complications. Mental retardation is attributed to ring chromosome X. The phenotype varies and not all abnormalities occur in all patients.
Klinefelter's syndrome
- genetic disease that produces sterile males with small testes lacking sperm due to XXY karyotype.
- A common sex chromosomal anomaly in males characterized mainly by small testes with tubular hyalinization, azospermia with infertility, slight breast enlargement, elevated urinary gonadotropins, and decreased urinary 17-ketosteroids. Dull mentality has been noted. The affected individuals appear normal after birth, except for small testes. Most characteristic features become evident at adolescence as hypogonadism, gynecomastia, incomplete virilization with variable eunuchoidism, and dull mentality. Without testosterone therapy, most adult patients may become obese. Occasional abnormalities may include cryptorchidism, hypospadias, ataxia, scoliosis during adolescence, and diabetes mellitus in adulthood.
Other conditions due to chromosome anomalies
Other conditions due to sex chromosome anomalies
Other conditions due to chromosome anomalies
Conditions due to anomaly of unspecified chromosome
- clinical conditions caused by an abnormal chromosome constitution in which there is extra or missing chromosome material, either a whole chromosome or a chromosome segment.
