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Pallister–Killian syndrome (also tetrasomy 12p mosaicism or Pallister mosaic aneuploidy syndrome) is an extremely rare genetic disorder occurring in humans. Pallister-Killian occurs due to the presence of the anomalous extra isochromosome 12p, the short arm of the twelfth chromosome. This leads to the development of tetrasomy 12p. Because not all cells have the extra isochromosome, Pallister-Killian is a mosaic condition.
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Characteristics include varying degrees of developmental disability, epilepsy, hypotonia, and both hypopigmentation and hyperpigmentation. Patients also exhibit a distinctive facial structure, characterized by high foreheads, sparse hair on the temple, a wide space between the eyes, epicanthal folds, and a flat nose. Vision and hearing impairments may occur. Patients may also exhibit congenital heart defects, gastroesophageal reflux, cataracts, and supernumerary nipples. Diaphragm problems seen in newborns can lead to death shortly after birth.
As patients pass into adolescence, the syndrome is characterized by a coarse and flat face, macroglossia prognathia, inverted lower lip, and psychomotor retardation with muscular hypertonia and contractures.
Pallister-Killian does not appear to be hereditary. Some research has suggested that the presence of the extra chromosome may be linked to premeiotic mitotic errors, both maternally and paternally. Several theories regarding the mechanism of this formation have been introduced.
The isochromosome can be primarily detected in samples of skin fibroblasts, as well as in chorionic villus and amniotic fluid cell samples. Very rarely, it can also be detected in blood lymphocytes. It is also possible to detect the isochromosome in circulating lymphocytes, as well as other amniotic and placental samples. There is no strict limit as to where the isochromosome can be found. However, it is often unlikely that these samples will be tested when the blood karyotype is normal.
Using an ultrasound, Pallister-Killian may be diagnosed through observation of hypertelorism, broad neck, shorts limbs, abnormal hands or feet, diaphragmatic hernia, and hydramnios. Once born, a child may be diagnosed by observation of the syndrome's distinct facial features.
- Peltomaki, P., S. Knuutila, A. Ritvanen et al. (1987). "Pallister-Killian syndrome: cytogenetic and molecular studies". Clin Genet 31 (6): 399–405. doi:10.1111/j.1399-0004.1987.tb02832.x. PMID 2887316.
- Polityko, A.D., E. Goncharova, L. Shamgina et al. (2005). "Pallister-Killian Syndrome : Rapid Decrease of Isochromosome 12p Frequency during Amniocyte Subculturing. Conclusion for Strategy of Prenatal Cytogenetic Diagnostics". Journal of Histochemistry and Cytochemistry 53 (3): 361–364. doi:10.1369/jhc.4A6402.2005. PMID 15750020.
- Hunter, A.G., B. Clifford, D.M. Cox (1985). "The characteristic physiognomy and tissue specific karyotype distribution in the Pallister-Killian syndrome". Clin Genet 28 (1): 47–53. doi:10.1111/j.1399-0004.1985.tb01217.x. PMID 4028501.
- Van Dyke, D.L., V.R. Babu, L. Weiss (1987). "Parental age, and how extra isochromosomes (secondary trisomy) arise". Clin Genet 32 (1): 75–9. doi:10.1111/j.1399-0004.1987.tb03328.x. PMID 3621657.
- Zambon, Francesco (2001-05-22). "Pallister-Killian syndrome". Medline Current Contents. Archived from the original on 2006-05-09. Retrieved 2006-05-31.