PallisterKillian

Pallister-Killian syndrome, also known as tetrasomy 12p mosaicism, is a rare genetic disorder caused by the presence of an extra isochromosome 12p in a mosaic pattern. In affected cells, there are four copies of the short arm of chromosome 12 (12p) due to an isochromosome 12p that arises after fertilization. Because mosaicism varies between tissues, the abnormal karyotype may not be detected in peripheral blood and is often identified through culture of skin fibroblasts or analysis of other affected tissues using cytogenetic or molecular methods.

Clinical features commonly include distinctive facial dysmorphisms such as a high broad forehead, sparse or absent eyebrows, ptosis, a wide nasal bridge, and micrognathia, along with ear anomalies. The skin frequently shows hypopigmented or speckled patches. Growth retardation and generalized hypotonia are typical in infancy, with congenital and developmental disabilities ranging from moderate to severe. Many individuals have congenital anomalies, including diaphragmatic hernia, heart defects, renal or urogenital anomalies, and limb differences. Neurological involvement is common, with severe to profound developmental delay and seizures occurring in a subset of patients.

Diagnosis relies on genetic testing of affected tissues rather than blood. Skin biopsy or another tissue sample analyzed by karyotyping, FISH, or array-based methods can reveal mosaic tetrasomy 12p, confirming the diagnosis. Prenatal detection is possible in some cases through fetal or placental testing.

Management is multidisciplinary and supportive, emphasizing early intervention, physical and occupational therapy, speech development, and monitoring and treatment of associated anomalies. The condition shows a wide phenotypic spectrum; prognosis varies with the extent of mosaicism and the presence of congenital anomalies.