We measured endogenous phosphorylation of peak II (apparent molecular weight of 220,000 daltons) of the erythrocyte membrane in 21 mothers of patients with Duchenne muscular dystrophy. The mean values of mothers with affected sons were significantly increased over those of matched controls (77.0 and 55.8 pmoles per milligram of 15-minute incubation; P less than 0.01). Detailed testing of mothers of affected sons revealed proximal muscle weakness. Seven mothers of isolated patients who had normal levels of creatine phosphokinase and no daughters with elevated levels were identified as carriers, because their mean value of peak II phosphorylation was increased (75.9 pmoles per milligram per 15 minutes) and equivalent to the level demonstrated in the 14 acknowledged carriers. Our results suggest that cases of Duchenne muscular dystrophy previously considered to be new mutations are much less common than estimated.

Female relatives of 41 Duchenne muscular dystrophy proband cases were studied with a panel of carrier-detection tests. A total of 277 relatives were tested in order to determine which mothers had affected sons as a result of new mutation. In 39 of 41 pedigrees the data demonstrate that a mutation cannot be postulated; the 2 megative pedigrees were inadequately tested. Our data suggest that all mothers of affected sons should be considered genetic carriers (heterozygotes) until proved otherwise. Our findings also raise questions concerning what mechanisms skew the indirect statistical estimates of mutation that are in common use.

SUMMARY1. 22Na and 42K radioisotopes were used to measure Na efflux and K influx in identical suspensions of fresh erythrocytes from myotonic dystrophy patients and matched controls under the same conditions and in the same time interval. K was present in concentration 10 mm in the suspending medium to prevent Na-for-Na exchange. Each flux was measured in the presence and absence of ouabain. The mean ouabainsensitive Na efflux rate in controls (2.33 + 0-13, s.E. of mean, m-equiv/l. cells. hr) was significantly greater (P < 0.001) than the corresponding rate in myotonic dystrophy (1P64 + 0.09).2. No significant differences between myotonic dystrophy and controls in mean ouabain-insensitive Na efflux, mean ouabain-sensitive K influx, or mean ouabain-insensitive K influx were found.3. The stoichiometric ratio (ouabain-sensitive Na efflux)/(ouabainsensitive K influx) was determined for each flux experiment. The mean stoichiometric ratio determined in controls (1 -46 + 0.08) reconfirms extensive previous evidence favouring a 3Na-for-2K active exchange in controls.4. The mean stoichiometric ratio determined in myotonic dystrophy (1.01 + 0 06) is statistically significantly different (P < 0 00 1) from that in controls. These findings are interpreted as indication of 2Na-for-2K exchange in erythrocytes from patients with myotonic dystrophy.

SUMMARY:A case of neonatal myasthenia gravis is reported in the infant of an asymptomatic thymectomized mother with comparably elevated acetylcholine receptor (AChR) antibody titers. The mother remained asymptomatic despite elevated antibody titers while the infant became asymptomatic in association with the disappearance of the AChR antibody. It is suggested that the AChR antibody plays an essential role in the development of neonatal myasthenia gravis. It is also suggested that a thymic factor is necessary for the development of clinical symptomatology accounting for the lack of correlation between the clinical state of the mother and infant.