Renal Growth in Isolated Methylmalonic Acidemia (MMA)

PURPOSE: We sought to predict renal growth based on clinical and metabolic parameters in patients with isolated methylmalonic acidemia (MMA), a group of disorders associated with chronic kidney disease. METHODS: Fifty MMA patients, followed from 2004 to 2011, were classified by molecular genetics and studied using a combined cross-sectional and longitudinal design that included renal ultrasound examinations, anthropometric measurements, and metabolic phenotyping. Renal length was compared to healthy controls and modeled to other clinical parameters using multiple regression analyses. RESULTS: Comparisons with age-matched controls showed that renal length in MMA subjects was significantly decreased (p < 0.05). Stepwise regression modeling found that combinations of height, serum cystatin C, and serum methymalonic acid concentrations best predicted kidney size. The regression equations used to generate MMA kidney nomograms were: renal length (cm) = 6.79 + 0.22 * age for the controls and 6.80 + 0.09 * age for the MMA cohort (p < 0.001; constant and slope). CONCLUSIONS: Renal length, reflective of kidney growth, significantly decreased in MMA patients over time compared to controls and was predictable with select clinical parameters. Cystatin C and serum methylmalonic acid concentrations were highly correlated with smaller kidneys and decreased renal function in this patient population.