Balanced translocation

An increased rate of chromosomal abnormalities has been reported for adult-onset schizophrenia (Karayiorgou and Gogos, 1997 Bassett et al., 2000). Cytogenetic abnormalities have been examined in the NIMH COS cohort. Five of our initial 54 patients had cytogenetic abnormalities (a girl with Turner s syndrome, a boy with a balanced translocation of chromosomes 1... 

Chronic myelogenous leukemia (CML) arises from a chromosomally abnormal hematopoietic stem cell in which a balanced translocation between the long arms of chromosomes 9 and 22, t(9 22), is observed in 90-95% of cases. This translocation results in expression of the Bcr-Abl fusion oncoprotein with a molecular weight of 210 kDa, which is constitutively expressed. The clinical symptoms and course are related to the white blood cell count and its rate of increase. Most patients with white cell counts over 50,000/ L should be treated. The goals of treatment are to reduce the... 

In addition, less extensively used diploid test systems include one type that reveals recessive lethals and balanced translocations and another type that measures the increased elimination of duplicated segments from duplicated strains. 

Trisomy 21 leads to the classical Down s syndrome balanced translocation results in the development of an apparently normal individual who can produce offspring with trisomy 21. Theoretically, the chances for a woman with a 15-21 translocation to produce a baby with Down s syndrome are 1 in 3 in reality the chances are only 1 in 5 because of the reduced viability of trisomic embryos. Translocation seldom causes trisomy, which most frequently results from nondisjunction. However, translocation is associated with a number of other congenital anomalies generally less severe than those observed in Down s syndrome. 

Studies have also been carried out on individuals with defective DNA repair and with chromosome instability syndromes. The baseline SCE frequency was found to be within the normal range in individuals with ataxia-telangiectasia, Fanconi s anemia, and xeroderma pigmentosum, but a greatly increased frequency of SCE appeared in both lymphocytes and cultured bone marrow cells from individuals with Bloom s syndrome. No deviation from the normal limits has been observed in individuals with Down s syndrome or with balanced translocations or unbalanced karyotypes. 

C. Stoll, D. S. Borgaonkar, and P. Bigel, Sister chromatid exchanges in balanced translocation carriers and in patients with unbalanced karyotypes, Hum. Genet. 37, 21-32 (1977). 

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