A new type of childhood leukemia in which a piece of chromosome 11 has been translocated (broken off and attached itself to another chromosome).Position 11q23 is the site of the mixed lineage leukemia gene – a gene so called because it has a gene expression profile different from that seen in other leukemias such as ALL and AML. Translocation affecting this gene is seen in as many as 80% of infants presenting with acute leukemia in the first 6 months of life. Infants with this type of leukemia have a particularly poor prognosis (outlook). They have high white blood counts and a high frequency of central nervous system involvement. They do not respond at all well to the standard therapies for ALL (acute lymphoblastic or lymphocytic leukemia) and often suffer from early relapse after chemotherapy translocation frequency at the MLL site declines with age and may be found in as few to 3% to 4% of adults with acute leukemia. Conventional chromosome analysis may miss this finding and molecular studies involving FISH (fluorescence in situ hybridization)methodology may be needed to detect it. MLL positive for translocation is a distinct entity separate from ALL, and requires other more aggressive therapies for treatment.
- Translocation, reciprocal
A type of chromosome rearrangement involving the exchange of chromosome segments between two chromosomes that do not belong to the same pair of chromosomes. A specific reciprocal translocation might, for example, involve the swap of material between chromosomes 1 and 19.
- Translocation, Robertsonian
A relatively very common and medically significant type of chromosome rearrangement that is formed by fusion of the whole long arms of two acrocentric chromosomes (chromosomes with the centromere near the very end). One in about 900 babies is born with a Robertsonian translocation making it the most common kind of chromosome rearrangement known in […]
- Transmissible spongiform encephalopathy
kuru; Creutzfeldt-Jakob disease; Gerstmann-Straussler syndrome; fatal familial insomnia; variant Creutzfeldt-Jakob disease (vCJD).
- Transmission distortion
meiotic drive which is preferential selection during meiosis (germ cell production); gametic selection which is preferential selection of gametes (germ cells) ; and postzygotic viability which reflects differences in the ability of conceptions to survive. All of these mechanisms for selection result in the production of offspring in proportions that deviate from Mendelian predictions. For […]
- Transmission, perinatal
Transmission of a disease-causing agent (a pathogen) from mother to baby during the perinatal period, the period immediately before and after birth. The perinatal period is defined in diverse ways. Depending on the definition, it starts at the 20th to 28th week of gestation and ends 1 to 4 weeks after birth. The perinatally transmitted […]