TCRAD, 14q11.2, Red
TCRAD, 14q11.2, Green
The TCRAD product consists of a 225kb probe, labelled in red, located at the centromeric end of the Variable Region of the immunoglobulin gene cluster, including the G36107 marker and a green probe covering a 143kb region located telomeric to the TRAC gene, including the entire OXA1L gene and the G35927 marker.
Chromosomal translocations with breakpoints in alpha and delta T-cell receptor (TCR) gene loci at 14q11.2 are recurrent in several T-cell malignancies including T-cell acute lymphoblastic leukaemia (T-ALL)1.
T-cell acute lymphoblastic leukaemia (T-ALL) is an aggressive malignancy of the lymphoblasts committed to the T-cell lineage and represents 15% of childhood and 25% of adult ALL2,3. Karyotyping reveals recurrent translocations that activate a small number of oncogenes in 25-50% of T-ALLs but, with FISH, further cryptic abnormalities can be revealed2.
The most common chromosomal rearrangements, found in about 35%2 of T-ALLs, involve the alpha and delta T-cell receptor loci (TRA and TRD) at 14q11.2, the beta TCR locus (TRB) at 7q34 and the gamma TCR (TRG) at 7p14. In most cases the juxtaposition of oncogenes next to the TCR regulatory sequences leads to the deregulated expression of these genes2,4,5.
The TRA/D complex at 14q11.2 has been shown to be involved in a number of different translocations in T-ALL. These include the t(10;14)(q24;q11) involving TLX1; the t(1;14)(p32;q11) involving TAL1; the t(14;21)(q11;q22) involving the OLIG2; the t(11;14)(p15;q11) involving LMO1 and the t(11;14)(p13;q11) involving LMO22.
In addition to T-ALL, TRA/D translocations are recurrent in T-non- Hodgkin’s lymphoma and T-prolymphocytic leukaemia. They have also been reported in cases of ataxia telangiectasia (AT)1.
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