Correlation between muscle atrophy, male hypogonadism and DNA expansion in myotonic dystrophy

The myotonic dystrophy (DM) mutation, identified as an unstable deoxyribonucleic acid (DNA) sequence, may increase the number of trinucleotide repeats in different tissues, producing various manifestations in skeletal muscles, in the gonads and in other organ systems. To evaluate gonadal function we investigated in 29 DM male patients and in 34 healthy subjects luteinizing hormone, follicle stimulating hormone, testosterone, free testosterone. The diagnosis was established by neurological examination, electromyography, muscle biopsy and DNA analysis. The mean age was 37.7 ± 10.8. The muscular clinical severity was scored as following Group A: only myotonia; group B: atrophy in distal muscles; group C: severe atrophy and/or manifesting weakness in distal muscles. The mean (CTG)(n) expansion was 756.8 ± 422.5, and in the group C the mean CTG expansion was significantly higher than in groups A and B (p < 0.006). Luteinizing hormone and follicle stimulating hormone levels (respectively 8.8 ± 4.7 mIU/ml, 19.2 ± 12.2 mIU/ml; p < 0.03) were higher and testosterone level (3.5 ± 2.72 ng/dl; p < 0.02) was lower in patients of group C (p < 0.03). There was a negative correlation between testosterone and free testosterone levels (respectively R = 0.56; p < 0.001; R = 0.59; p < 0.001) and the duration of disease. In our DM patients a significant correlation between muscular score, gonadotrophin levels and DNA expansion was found. In a previous study different expansion in spermatozoa and muscle tissue was demonstrated. We conclude that a somatic mosaicism is present in different tissues and possibly the different clinical signs in myotonic dystrophy patients are in relationship to that.