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Medical Definition of Chromosome 15
1. Mosaic trisomy 15 is reported with no major or visible dysmorphia and severe inner organ defect. Duplication in the 15q11-13 region is also reported, although rarely, and can be associated with Prader-Willi syndrome. The phenotype includes developmental delay, particularly concerning acquisition of speech, ataxic gait with similarities to Angelman syndrome and seizures. Craniofacial dysmorphism includes oval face, high cheekbones and deep orbits. The trisomy can result from a malsegregation of a parental translocation, or can occur de novo with the presence of a supernumerary acrocentric chromosome of the size of a G-group chromosome or a supernumerary chromosome carrying satellites at both extremities. The latter rearrangement causes partial 15 tetrasomy results from an inverted duplication of chromosome 15. Patients with inv dup(15) show normal growth, moderate to severe mental retardation, seizures, poor motor coordination, behavioural problems, autism and mild dysmorphic features. Triplication in the same 15q11-13 region is also reported. Clinically, the patients present with hypotonia, developmental delay, visual impairment and minor dysmorphic features. 15q2 trisomy results from malsegregation of a parental translocation and shows a highly characteristic craniofacial dysmorphism including microdolichocephaly, narrow palpebral fissures, protuberant philtral borders and micrognathia. Various osteoarticular anomalies are observed. Inner organ malformations include heart disease. Mental retardation is severe. Prader-Willi syndrome and Angelman syndrome are distinct mental retardation disorders which result from paternal and maternal deficiency, respectively, for chromosome 15q11-q13. Approximately half of the patients with Prader-Willi syndrome show microscopically detectable paternally derived deletions, duplications and other chromosomal rearrangements of 15q11.2, or maternal uniparental disomy for chromosome 15. In contrast, Angelman syndrome can result from either maternally inherited deletions of this region or paternal uniparental disomy for chromosome 15. Major features of Prader-Willi syndrome include neonatal hypotonia with feeding difficulties, poor spontaneous movement, spells of cyanosis, a weak or absent cry, hypogonadism with cryptorchidism, mental retardation, obesity, hyperphagia and short stature. Features of Angelman syndrome include severe mental deficiency, ataxic (puppet-like) gait, prognathia and wide mouth, seizures and paroxysmal laughter. The phenotype of an interstitial deletion 15q13 includes gross congenital anomalies consisting of large fontanelles and sutures, midface hypoplasia, flat ears with thin cartilage, prominent eyes, anteverted nostrils, cleft palate, positional deformation of hands and feet, hypertonia and inner organ malformations. The phenotype shows few overlapping features with Prader-Willi syndrome or Angelman syndrome. Ring chromosome 15 is a rare cytogenetic disorder characterised by growth retardation, microcephaly, triangular facies, hypertelorism, brachydactyly, variable mental retardation and speech delay. Gene assignments to chromosome 15 include the gene coding for hexosaminidase-A, whose mutation causes Tay-Sachs disease, and the major gene for Marfan syndrome. (05 Mar 2000)
Lexicographical Neighbors of Chromosome 15
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