Vitamin D deficiency in myotonic dystrophy type 1

Area of Science:

• Endocrinology
• Neuromuscular Disorders
• Metabolic Bone Disease

Background:

• Myotonic dystrophy type 1 (DM1) is a multisystemic disorder impacting the endocrine system and steroid hormone function.
• Vitamin D, a steroid hormone, plays a crucial role in calcium homeostasis and muscle metabolism.
• Vitamin D influences muscle trophism via genomic and non-genomic pathways, including the stimulation of insulin-like-growth-factor 1 (IGF1).

Purpose of the Study:

• To investigate vitamin D deficiency in DM1 patients.
• To explore the relationship between vitamin D levels, IGF1, muscle strength, and genotype in DM1.
• To assess the efficacy of vitamin D supplementation in DM1 patients.

Main Methods:

• Serum 25-hydroxyvitamin D (25(OH)D), calcium, parathormone (PTH), and IGF1 levels were measured in 32 DM1 patients and 32 controls.
• Bone mineral density (BMD) and proximal muscle strength were assessed.
• Correlation analyses were performed between 25(OH)D levels, CTG repeat expansion size, IGF1, and muscle strength.

Main Results:

• DM1 patients exhibited significantly lower 25(OH)D and IGF1 levels compared to controls.
• Reduced 25(OH)D levels inversely correlated with CTG expansion size.
• IGF1 levels and muscle strength showed a positive correlation with 25(OH)D levels, particularly below 20 and 10 ng/ml, respectively.
• A higher prevalence of hyperparathyroidism was observed in DM1 patients.
• Oral cholecalciferol supplementation normalized 25(OH)D levels, indicating no absorption or hepatic hydroxylation defects.

Conclusions:

• DM1 patients present with reduced circulating 25(OH)D levels, linked to genotype.
• Vitamin D deficiency in DM1 may impact IGF1 levels and proximal muscle strength.
• Vitamin D supplementation is a potential therapeutic strategy to mitigate muscle weakness in DM1.