A loss-of-function polymorphic mutation in the cytolytic P2X7 receptor gene and chronic lymphocytic leukaemia: a molecular study.
BACKGROUND
Chronic lymphocytic leukaemia (CLL) has a familial incidence nearly three times higher than expected for the general population and one predisposing factor might be an inherited failure of mechanisms involved in apoptosis of lymphocytes. Our aim was to ascertain whether or not a defect in a proapoptotic pathway, caused by a single nucleotide polymorphism that results in loss-of-function of P2X7 in healthy individuals, was present in leukaemic B lymphocytes of patients with CLL.


METHODS
We extracted genomic DNA from the peripheral blood leucocytes of 36 unrelated individuals with CLL, four individuals with familial CLL, and 46 age-matched controls. We sequenced a PCR product to detect mutations in exon 13 of P2X7. In most patients with CLL, we measured expression and function of the P2X7 receptor by flow cytometry in B lymphocytes and T lymphocytes.


RESULTS
The prevalence of the polymorphic mutation and the frequency of the mutant allele were three-fold greater in individuals with CLL than in white, elderly controls. Individuals homozygous for the polymorphic allele had no P2X7 receptor function and heterozygotes had half the mean function of that seen in individuals homozygous for the wildtype allele; amounts of ATP-induced apoptosis varied accordingly. In two families, in which we studied a father-son pair and a sister-sister pair with CLL, loss of P2X7 function arose because of inheritance of one or two 1513A-->C alleles for P2X7.


CONCLUSIONS
Activation of the P2X7 receptor leads to apoptosis of lymphocytes in individuals with CLL, and reduced function of this receptor has an anti-apoptotic effect, resulting in an increase in B-cell numbers. Thus, inheritance of a loss-of-function polymorphic mutation at position 1513 in the P2X7 gene could contribute to the pathogenesis of CLL.
Wiley
James S
JS
Sydney University Department of Medicine, Nepean Hospital, PO Box 63, New South Wales, 2751, Penrith, Australia. wileyj@medicine.usyd.edu.au
Dao-Ung
L Phuong
LP
Gu
Ben J
BJ
Sluyter
Ronald
R
Shemon
Anne N
AN
Li
Changping
C
Taper
John
J
Gallo
John
J
Manoharan
Arumugam
A
D000368:Aged; D000483:Alleles; D017209:Apoptosis / Q000235:genetics; D001402:B-Lymphocytes / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D005260:Female; D015973:Gene Expression Regulation, Leukemic; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D018048:Receptors, Purinergic P2 / Q000235:genetics* / Q000502:physiology; D058486:Receptors, Purinergic P2X7
C546468:P2RX7 protein, human; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7