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

Analysis of human urinary extracellular vesicles reveals disordered renal metabolism in myotonic dystrophy type 1

Chronic kidney disease (CKD) and the genetic disorder myotonic dystrophy type 1 (DM1) each are associated with progressive muscle wasting, whole-body insulin resistance, and impaired systemic metabolism. However, CKD is undocumented in DM1 and the molecular pathogenesis driving DM1 is unknown to involve the kidney. Here we use urinary extracellular vesicles (EVs), RNA sequencing, droplet digital PCR, and predictive modeling to identify downregulation of metabolism transcripts Phosphoenolpyruvate carboxykinase-1, 4-Hydroxyphenylpyruvate dioxygenase, Dihydropyrimidinase, Glutathione S-transferase alpha-1, Aminoacylase-1, and Electron transfer flavoprotein B in DM1. Expression of these genes localizes to the kidney, especially the proximal tubule, and correlates with muscle strength and function. In DM1 autopsy kidney tissue, characteristic ribonuclear inclusions are evident throughout the nephron. We show that urinary organic acids and acylglycines are elevated in DM1, and correspond to enzyme deficits of downregulated genes. Our study identifies a previously unrecognized site of DM1 molecular pathogenesis and highlights the potential of urinary EVs as biomarkers of renal and metabolic disturbance in these individuals.

Kidney Function in Patients With Neuromuscular Disease: Creatinine Versus Cystatin C

Background: Accurate measurement of kidney function in patients with neuromuscular disorders is challenging. Cystatin C, a marker not influenced by skeletal muscle degradation, might be of clinical value in these patients.

Methods: We consecutively enrolled 39 patients with neuromuscular disorders. We investigated the association of the eGFR, based on plasma creatinine and Cystatin C, with clinical and biochemical variables associated with kidney function, namely age and galectin-3.

Results: Creatinine-based eGFR was 242 (±80) and Cystatin C-based eGFR was 110 (±23) mL/min/1.73 m². Cystatin C-based eGFR was associated with age (β −0.63 p < 0.0001) and galectin-3 levels (β −0.43 p < 0.01), while creatinine-based eGFR was not (β −0.22 p = 0.20; β −0.28 p = 0.10). Sensitivity analyses in Duchenne and Becker patients revealed the same results: Cystatin C-based eGFR was associated with age (β −0.61 p < 0.01) and galectin-3 levels (β −0.43 p = 0.05), while creatinine-based eGFR was not (β −0.32 p = 0.13; β −0.34 p = 0.14).

Conclusions: These data indicate that estimation of renal function in patients with neuromuscular disorders cannot reliably be achieved with creatinine, while Cystatin C appears a reasonable alternative. Since a large proportion of patients with neuromuscular disorders develops heart failure, and requires heart failure medication, adequate monitoring of renal function is warranted.

Three-dimensional imaging in myotonic dystrophy type 1: Linking molecular alterations with disease phenotype

Objective

We aimed to determine whether 3D imaging reconstruction allows identifying molecular:clinical associations in myotonic dystrophy type 1 (DM1).

Methods

We obtained myoblasts from 6 patients with DM1 and 6 controls. We measured cytosine-thymine-guanine (CTG) expansion and detected RNA foci and muscleblind like 1 (MBNL1) through 3D reconstruction. We studied dystrophia myotonica protein kinase (DMPK) expression and splicing alterations of MBNL1, insulin receptor, and sarcoplasmic reticulum Ca(2+)-ATPase 1.

Results

Three-dimensional analysis showed that RNA foci (nuclear and/or cytoplasmic) were present in 45%-100% of DM1-derived myoblasts we studied (range: 0-6 foci per cell). RNA foci represented <0.6% of the total myoblast nuclear volume. CTG expansion size was associated with the number of RNA foci per myoblast (r = 0.876 [95% confidence interval 0.222-0.986]) as well as with the number of cytoplasmic RNA foci (r = 0.943 [0.559-0.994]). Although MBNL1 colocalized with RNA foci in all DM1 myoblast cell lines, colocalization only accounted for 1% of total MBNL1 expression, with the absence of DM1 alternative splicing patterns. The number of RNA foci was associated with DMPK expression (r = 0.967 [0.079-0.999]). On the other hand, the number of cytoplasmic RNA foci was correlated with the age at disease onset (r = -0.818 [-0.979 to 0.019]).

Conclusions

CTG expansion size modulates RNA foci number in myoblasts derived from patients with DM1. MBNL1 sequestration plays only a minor role in the pathobiology of the disease in these cells. Higher number of cytoplasmic RNA foci is related to an early onset of the disease, a finding that should be corroborated in future studies.

Clinical Care Recommendations for Cardiologists Treating Adults With Myotonic Dystrophy

Myotonic dystrophy is an inherited systemic disorder affecting skeletal muscle and the heart. Genetic testing for myotonic dystrophy is diagnostic and identifies those at risk for cardiac complications. The 2 major genetic forms of myotonic dystrophy, type 1 and type 2, differ in genetic etiology yet share clinical features. The cardiac management of myotonic dystrophy should include surveillance for arrhythmias and left ventricular dysfunction, both of which occur in progressive manner and contribute to morbidity and mortality. To promote the development of care guidelines for myotonic dystrophy, the Myotonic Foundation solicited the input of care experts and organized the drafting of these recommendations. As a rare disorder, large scale clinical trial data to guide the management of myotonic dystrophy are largely lacking. The following recommendations represent expert consensus opinion from those with experience in the management of myotonic dystrophy, in part supported by literature-based evidence where available.

Changes of nutritional status and the variations of serum indicators of patients with chronic kidney disease accompanied by hypothyroidism taking thyroid hormone replacement therapy as the therapeutic models

This study aimed to analyze the incidence of malnutrition in patients with chronic kidney disease (CKD) at stage III-IV accompanied by hypothyroidism and indicate the improvement in nutritional status and kidney disease of CKD patients after undergoing thyroid hormone replacement (THR) therapy as therapeutic models. The included 156 CKD patients in stage III-IV were divided into the CKD stage III group (CKD-III group) (n = 80) and CKD stage IV group (CKD-IV group) (n = 76), and the clinical indicators of all the patients were collected. Based on changes in thyroid function, the included patients were again divided into the following groups: subclinical hypothyroidism group (the experimental group, hereinafter referred to Y-group, n = 78) and non-subclinical hypothyroidism group (the control group, hereinafter referred to N-group, n = 78), in which the CKD-III group was divided into CKD-IIIN group (n = 38) and CKD-IIIY group (n = 42), and also the CKD-IV group was divided into CKD-IVN group (n = 40) and CKD-IVY group (n = 36). At the beginning, patients in the Y-group was orally given 25 μg/dL of levothyroxine; based on the progression of the disease, the dosage was regulated; the concentration of serum thyroid stimulating hormone (TSH) was assessed once per month, as well as changes in tri-iodothyronine (T3) and tetraiodothyronine (T4). Estimated glomerular filtration rate (eGFR) in the CKD-IIIY group was significantly changed compared with that of the CKD-IVY group after THR therapy. Comparison of nutrition-based indicators between the N-group and the Y-group showed that the serum albumin (ALB) level, the hemoglobin (HGB) level, and the grip strength of both the left and right hand were notably decreased (P < 0.05). After THR therapy, the indicators related to CKD patients were accompanied by subclinical hypothyroidism changes; the levels of ALB and HGB, as well as the grip strength of both the left and right hand were notably increased compared with before undergoing THR therapy (P < 0.05). In conclusion, malnutrition of chronic kidney disease caused by subclinical hypothyroidism could be partially recovered after THR therapy as therapeutic models.

Renal involvement in the pathogenesis of mineral and bone disorder in dystrophin-deficient mdx mouse

Duchenne muscular dystrophy is a severe muscular disorder, often complicated with osteoporosis, and impaired renal function has recently been featured. We aimed to clarify the involvement of renal function in the pathogenesis of mineral and bone disorder in mdx mice, a murine model of the disease. We clearly revealed renal dysfunction in adult mdx mice, in which dehydration and hypercalcemia were contributed. We also examined the effects of dietary phosphorus (P) overload on phosphate metabolism. Serum phosphate and parathyroid hormone (PTH) levels were significantly increased in mdx mice by dietary P in a dose-dependent manner; however, bone alkaline phosphatase levels were significantly lower in mdx mice. Additionally, bone mineral density in mdx mice were even worsened by increased dietary P in a dose-dependent manner. These results suggested that the uncoupling of bone formation and resorption was enhanced by skeletal resistance to PTH due to renal failure in mdx mice.