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Medical Definition of Chromosome 8
1. Trisomy 8 mosaicism, one of the major cytogenetic syndromes, is characterised by a very suggestive facial dysmorphism, as well as osteoarticular anomalies. Craniofacial dysmorphism includes long face, lop-ear deformities, prominent forehead and overhang of lower lip. Osteoarticular anomalies include camptodactyly, brachydactyly or arachnodactyly, clinodactyly, clubfoot and joint contractures leading to permanent deformities. Deep palmar and plantar creases can be noted in young infants. Skeletal malformations are frequent and severe. Inner organ malformations are rare and kidney or congenital heart defect can be observed. Mental deficiency is not very pronounced. 8p monosomy often occurs de novo. Patients present with a small skull with protruding occiput, short nose, small mouth, and a short and wide neck. Cardiac malformations are frequent. The degree of mental retardation is variable. Inverted duplications of chromosome 8p with distal deletion of 8p are reported. Common clinical traits are hypotonia at birth, large mouth with thin upper lip, bulbous and broad nose, malformed ears, hand and feet anomalies and severe mental retardation. 8p trisomy can result from a parental translocation or can occur de novo. Patients have high prominent forehead, everted fleshy lower lip and flexion contractures of the limbs. Cardiac and cerebral malformations can be observed. Mental retardation is considerably more severe than with trisomy 8 mosaicism. Mosaic tetrasomy 8p resulting from an isochromosome 8p was described. The clinical phenotype can overlap in part with those of trisomy 8 or trisomy 8p, but shows distinctive features including agenesis of the corpus callosum, cardiac malformations and minimal facial dysmorphism. 8q2 trisomy usually results from a parental translocation or inversion. The phenotype includes prominent forehead with hypertelorism, very wide bridge of the nose with blunt nasofrontal angle, microretrognathia, detached and poorly folded ears, buccal deformities including bifid tip of the tongue, cleft upper gum, high arched or cleft palate and bifid uvula. Joint contractures are also noted. Cardiac malformations are frequent and severe. Mental retardation is variable. The Langer-Giedion syndrome, characterised by craniofacial dysmorphism and skeletal abnormalities, is caused by a genetic defect in 8q24.1. Among the gene assignments known for chromosome 8 is the gene for glutathione reductase, the deficiency of which causes a variety of haemolytic anaemia. (05 Mar 2000)
Lexicographical Neighbors of Chromosome 8
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