Immunodeficiency in ataxia telangiectasia is correlated strongly with the presence of two null mutations in the ataxia telangiectasia mutated gene

Abstract

Immunodeficiency affects over half of all patients with ataxia telangiectasia (A-T) and when present can contribute significantly to morbidity and mortality. A retrospective review of clinical history, immunological findings, ataxia telangiectasia mutated (ATM) enzyme activity and ATM mutation type was conducted on 80 consecutive patients attending the National Clinic for Ataxia Telangiectasia, Nottingham, UK between 1994 and 2006. The aim was to characterize the immunodeficiency in A-T and determine its relationship to the ATM mutations present. Sixty-one patients had mutations resulting in complete loss of ATM kinase activity (group A) and 19 patients had leaky splice or missense mutations resulting in residual kinase activity (group B). There was a significantly higher proportion of patients with recurrent sinopulmonary infections in group A compared with group B (31 of 61 versus four of 19 P = 0.03) and a greater need for prophylactic antibiotics (30 of 61 versus one of 19 P = 0.001). Comparing group A with group B patients, 25 of 46 had undetectable/low immunoglobulin A (IgA) levels compared with none of 19; T cell lymphopenia was found in 28 of 56 compared with one of 18 and B cell lymphopenia in 35 of 55 compared with four of 18 patients (P = 0.00004, 0.001 and 0.003 respectively). Low IgG2 subclass levels and low levels of antibodies to pneumococcal polysaccharide were more common in group A than group B (16 of 27 versus one of 11 P = 0.01; 34/43 versus six of 17 P = 0.002) patients. Ig replacement therapy was required in 10 (12.5%) of the whole cohort, all in group A. In conclusion, A-T patients with no ATM kinase activity had a markedly more severe immunological phenotype than those expressing low levels of ATM activity.

Fig. 1

Serum immunoglobulin A (IgA) levels in ataxia telangiectasia patients. IgA levels in 46 group A patients [with no ataxia telangiectasia mutated (ATM) kinase activity] and 19 group B patients (some residual ATM kinase activity). Limit of detection for IgA was 0·07 g/l. Age-related normal reference ranges are taken from Protein Reference Unit Handbook of Clinical Immunochemistry, 8th edition [17].

Fig. 2

Serum immunoglobulin G2 (IgG2) levels in ataxia telangiectasia patients. IgG2 levels in 27 group A patients [with no ataxia telangiectasia mutated (ATM) kinase activity] and 11 group B patients (some residual ATM kinase activity). Age-related normal reference ranges are taken from Protein Reference Unit Handbook of Clinical Immunochemistry, 8th edition [17].

Fig. 3

T lymphocyte counts in ataxia telangiectasia patients. Absolute numbers in 56 group A patients [with no ataxia telangiectasia mutated (ATM) kinase activity] and 18 group B patients (some residual ATM kinase activity). Age-related normal reference ranges are taken from Comans-Bitter et al. [18].

Fig. 4

B lymphocyte counts in ataxia telangiectasia patients. Absolute numbers in 55 group A patients [with no ataxia telangiectasia mutated (ATM) kinase activity] and 18 group B patients (some residual ATM kinase activity). Age-related normal reference ranges are taken from Comans-Bitter et al. [18].