Chromosome 12
Several types of cancer are due to changes in chromosome 12. These genetic changes are somatic, which means that they are acquired during the life of a person and are present only in certain cells. For example, rearrangements (translocations) of genetic material between chromosome 12 and other chromosomes are often found in certain blood-forming cell cancers (leukemia) and immune system cell cancers (lymphomas). In addition, somatic mutations can lead to an additional copy of chromosome 12 (trisomy 12) in cancer cells, specifically a type of leukemia called Chronic lymphocytic leukemia.
Translocations have also been found that involve chromosome 12 in solid tumors such as lipomas and liposarcomas, which are formed by fatty tissue. Chromosome 12 abnormalities have been identified in at least two other rare tumors, angiomatoid fibrous histiocytomas and clear cell sarcomas. Angiomatoid fibrous histiocytomas occur mainly in adolescents and young adults and are usually found in the arms and legs (limbs). Clear cell sarcomas occur most often in young adults and tend to be associated with tendons and related structures called aponeurosis.
Pallister-Killian syndrome is usually caused by the presence of an extra abnormal chromosome called ispromosome 12p. An isochromosome is a chromosome with two identical arms. Normal chromosomes have a long (q) and a short (p) arm, but isochromosomes have two equal arms. Which means that some body cells have a 12p tetrasomy. Pallister-Killian syndrome occurs in mosaic, it is a developmental disorder that affects many parts of the body. This condition is characterized by an extremely weak muscle tone (hypotonia) in childhood and early childhood, intellectual disability, distinctive facial features, poor hair, areas of unusual skin coloration (pigmentation) and other congenital defects.
Chronic eosinophilic leukemia is associated with PDGFRB. This condition is characterized by a greater number of eosinophils, a type of white blood cell. The most common translocation that causes this condition fuses part of the PDGFRB gene on chromosome 5 with part of the ETV6 gene on chromosome 12, written as t (5; 12) (q31-33; p13). These translocations are acquired during a person's life and are present only in cancer cells. When the mutation of the ETV6-PDGFRB fusion gene occurs in cells that turn into blood cells, the growth of eosinophils (and occasionally other white blood cells, such as neutrophils and mast cells) is poorly controlled, leading to chronic eosinophilic leukemia associated with PDGFRB.
Other changes in the number or structure of chromosome 12 can cause a variety of effects on health and development. These effects include intellectual disability, slow growth, distinctive facial features, weak muscle tone (hypotonia), skeletal abnormalities and heart defects.
Several different changes related to chromosome 12 have been reported, including an extra piece of chromosome in each cell (partial trisomy 12), a missing segment of the chromosome in each cell (partial monosomy 12) and a circular structure called ring chromosome 12 .
