Reduced renal function in patients with Myotonic Dystrophy type 1 and the association to CTG expansion and other potential risk factors for chronic kidney disease.

Myotonic dystrophy type 1 (DM1) affects several organs. Disease severity and age at onset are correlated to the CTG repeat expansion. The aim of this study was to assess renal function and the association to numbers of CTG repeat expansion in patients with DM1. Ninety-eight patients with DM1 were included. Glomerular filtration rate (measured GFR) was measured using iohexol clearance. Data on CTG repeats were available in 83/98 (85%) patients. The overall mGFR was 74 (16) ml/min/1.73 m (range 38-134). Sixty-four patients (69%) had a mild and sixteen patients (17%) a moderate decrease in renal function (mGFR 60-89 and 30-59 ml/min/1.73 m, respectively). No correlations were found between CTG repeats and mGFR (r = 0.10, p = 0.4) or between CTG repeats and serum cystatin C (r = 0.12, p = 0.29). CTG repeats was positively correlated to creatinine-based estimates of GFR (eGFR) (modified diet in renal disease r = 0.49, p < 0.001, CKD-EPI creatinine equation; r = 0.50, p < 0.001), but analyses using Structural Equation Modeling showed no correlation. The correlation was explained by an indirect effect via serum creatinine and skeletal muscle mass index. In conclusion, patients with DM1 seem to have a slight decrease in renal function but there is no association between renal function and the number of CTG repeats, a marker of disease severity.