Among the multisystem consequences of myotonic dystrophy, patients are at risk of renal dysfunction. A recent paper by Dr. Tsuyoshi Matsumura (National Hospital Organization Toneyama National Hospital, Japan) and colleagues evaluated circulating cystatin C (CysC) levels in patients with a variety of neuromuscular diseases and found the highest levels in DM1, potentially predictive of subsequent kidney damage and failure. These data stress that renal function monitoring, via CysC levels, should be an important component of care for individuals with DM1. The assessment of renal dysfunction in neuromuscular disease is complicated by the fact that creatinine, which increases in renal dysfunction, declines in parallel with skeletal muscle loss. By contrast, cystatin C (CysC) levels also represent an indicator of kidney function, but one that is not affected by changes variables such as muscle volume, food intake, or exercise.

Thus CysC, as well as the glomerular filtration rate of CysC (GFRcys), constitute superior biomarkers of kidney function when the disease process itself impacts serum creatinine levels. Dr. Matsumura and his colleagues retrospectively studied a cohort of 586 patients with neuromuscular disease (141 with DM1), using a variety of renal function measures to evaluate the relative risks for development of kidney disease. None of the subjects had signs of renal dysfunction at the time of analysis. After controlling for baseline age and gender differences, cross-disease comparisons showed that elevation in CysC and reduction in GFRcys were most pronounced in individuals with DM1, suggesting that they were at the highest risk for kidney failure.

The study also showed that there was a modest correlation between expanded CTG repeat length and CysC levels. Finally, the authors reported findings from two DM1 autopsies, where nephrosclerotic changes were observed relatively early in disease course  (both subjects in their 40’s); although CysC levels were not available for these subjects, these data support the need for further study of the natural history of kidney dysfunction in DM1, to determine best practices for patient care.

Elevated CysC has previously been reported in neuromuscular disease patients with renal dysfunction or failure, and has been suggested as a safety biomarker for interventional clinical trials in these diseases. Findings by Dr. Matsumura’s team suggest that DM1 patients may be at greater risk for kidney dysfunction and failure than those with other neuromuscular diseases. Moreover, CysC levels may be an important biomarker for careful management of DM, as well as for safety assessments of interventions in DM1 clinical trials.

Reference:

"Renal dysfunction can be a common complication in patients with myotonic dystrophy 1."
Matsumura T, Saito T, Yonemoto N, Nakamori M, Sugiura T, Nakamori A, Fujimura H, Sakoda S.
J Neurol Sci. 2016 Sep 15;368:266-71. doi: 10.1016/j.jns.2016.07.036. Epub 2016 Jul 15.