The incidence of leukemias is about 10 per 100 000 per annum in all types of population. 50% of them are acute leukemias. ALL occurs at an annual rate of approximately 30 to 40 per million. There are approximately 2,400 children and adolescents younger than 20 years diagnosed with ALL each year in the United States (Leukemia, US NIHS). The male: female ratio is about 3:2 in acute leukemia, 2:1 in CLL and 1.3:1 in CML. CLL is rare in Chinese and related races. Though acute leukemias occur at all ages, they are lowest amongst the young and highest after 50 years of age. ALL is more incident in young children between 1-5 years. CLL and CML are mainly diseases of middle age and beyond. CML occurs between 30 and 80 years with a peak at 55 years of age. AML is four times more common than ALL in adults.1. Genetic factors: There are some families with an excessive incidence of leukemias. There is high concordance among identical twins if acute leukemia occurs in the first year of life. Also, the incidence of leukemia is high in various congenital genetic disorders like Downs syndrome, Blooms Syndrome, Klinefelters syndrome, etc. In chronic granulocytic leukemia, an abnormality in chromosome 21 has been detected. This abnormal chromosome is called the Philadelphia chromosome (Ph-1) and is characterized by the absence of a part of one of its long arms (Shafer, 161).2. Environmental factors: Studies have shown that ionizing radiation causes leukemia in experimental animals. There has been an increased incidence of leukemia in the survivors of Japanese bomb explosions and those exposed to occupational radiation. Also, those receiving radiation therapies for various causes including spondylitis may be at increased risk for leukemia. Chromosomal translocations involving the Nucleophosmin gene occur frequently in myeloid and lymphoid cancers. This gene is a multifunctional phosphoprotein to which both tumor-suppressor and oncogenic functions have been attributed (Grisendi, 291- 292).
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