Duchenne/Becker muscular dystrophy (DBMD) are viewed as diseases in which pulmonary function plateaus then predictably declines. However, we have observed pulmonary function variability among brothers with DBMD despite identical genetic defects. Purpose: to quantify pulmonary function variability among brothers with DBMD in our clinic.
Retrospective chart review January 1992-March 2009. We calculated the difference in peak FVC between the “strong” and “weak” brother in each fraternal pair. Then, we compared the mean FVC differences between the brothers with concordant pulmonary function versus the brothers with discordant pulmonary function with aging. Exclusion criteria: steroid therapy, residence apart, non-neuromuscular respiratory diagnoses. Each patient reached peak FVC before major respiratory illness, cardiomyopathy or noninvasive ventilation.
Among 97 patients were 7 eligible sibships. 6 sibships contained 2 brothers and one had 3 brothers. Peak pulmonary function occurred at mean age (+/− SD) 14.31 +/− 2.18 years (n = 15). 3 sets of brothers had discordant pulmonary function and 4 sets of brothers had concordant pulmonary function. In the 4 sibships with concordant pulmonary function, mean peak FVC difference between brothers was 0.32 +/− 0.21 liters. In the 3 sibships with discordant pulmonary function, mean peak FVC difference between brothers was 1.00 +/− 0.20 liters (p < 0.01). In the discordant group, the brother with highest peak FVC maintained a superior FVC with aging. Mean difference in the percent predicted FVC between the brothers at their oldest comparable age was 28.5% +/− 16% in the discordant group and 5.3% +/− 4.4% in the concordant group (p < 0.04)at mean age 19.2 +/− 3.8 years.
Pulmonary function variability among our brothers with DBMD was common: despite identical genetic defects, we found discordant FVC values among brothers in 3 of 7 sibships. The brother with highest peak FVC level maintained his superior FVC with aging.
Variability in pulmonary function may limit use of genetic testing to predict respiratory course/prognosis in patients with DBMD. Peak FVC level may predict future pulmonary function in DBMD patients.
David Birnkrant, No Financial Disclosure Information; No Product/Research Disclosure Information