MYOADENYLATE DEAMINASE DEFICIENCY: DIAGNOSIS BY FOREARM ISCHEMIC EXERCISE TESTING AND PLASMA PURINE MEASUREMENTS.: 216

Abstract

Quantitation of lactate and ammonia (NH3) production after forearm ischemic exercise (FIE) has been proposed as a screening test for myoadenylate deaminase (MAD) deficiency. Plasma lactate, NH3 and purines (adenosine inosine, hypoxanthine, xanthine) were determined 1, 3, 5 and 10 minutes after 90 seconds of FIE and correlated with exercise performance (∑ kg × sec), measured with a grip dynamometer, strain gauge and strip recorder.In 13 normals lactate and NH3 production correlated with exercise performance (r=0.76 and 0.72, respectively). Three patients with histochemically-defined MAD deficiency failed to generate NH3 despite increasing lactate and adequate performance. Retesting normals at submaximal performance produced lactate and NH3 generation patterns indistinguishable from those of the 3 patients. Normal subjects even with submaximal performance increased plasma purines from 10 to 38 μM after FIE. The MAD deficient patients raised their purine levels only 0-7 μM.These data demonstrate that submaximal exercise efforts by normals can give FIE test results indistinguisable from those of MAD deficient individuals if only lactate and NH3 are assessed and plasma purine measurements after FIE testing are effective in identifying the deficiency state. These results support the hypothesis that disordered purine metabolism occurs in patients with MAD deficiency.