Blind evaluation of lymphocyte capping in Duchenne muscular dystrophy

Recently, Pickard et al reported decreased "capping" in lymphocytes from patients with Duchenne type muscular dystrophy (DMD) as well as female carriers of the DMD trait. To resolve subsequent debate about the reproducibility of this finding, we carried out a "blinded" collaborative study designed to eliminate the possibility of observer bias. Blood samples from DMD patients, their mothers, and controls were obtained and coded at Johns Hopkins and transported to the Medical College of Virginia, where lymphocyte capping was tested using FITC-labeled polyvalent anti-human immunoglobulin. Diminished capping in lymphocytes was found in 12 of 13 DMD patients (17 of 18 blood samples) and in 14 of 17 mothers of DMD patients (19 of 23 blood samples), as compared with 8 of 21 control subjects (8 of 22 blood samples). The results in both the patient and the carrier groups differed significantly from those in the control group, confirming previous observations of diminished lymphocyte capping in DMD. The findings provide support for the concept of a systemic defect associated with cell membranes in this disorder. The relatively high incidence of false positive results limits the usefulness of lymphocyte capping as a diagnostic test for carriers under the conditions of this study.