Amyotrophic lateral sclerosis: unusually low content of collagen in skin.

The skin tissues from patients with amyotrophic lateral sclerosis (ALS) and controls were studied by electron microscopy, and their amino acid compositions were examined. On electron microscopy, the most conspicuous findings in ALS were (1) a marked increase in amorphous material separating collagen bundles, and (2) the smaller diameter of collagen fibrils. These were more marked with longer duration of illness. Amino acid analysis showed that the levels of hydroxyproline, hydroxylysine, and glycine were significantly low (P less than 0.001, P less than 0.01, and P less than 0.001, respectively) in ALS patients as compared with those of controls, and there was a significant negative correlation between the level of hydroxyproline and duration of illness in ALS patients (r = -0.88, P less than 0.01). In addition, the collagen content per dry weight (mg) of the tissues in ALS was significantly smaller (P less than 0.001) than in controls. These results indicate that the metabolism of skin collagen might be affected in the disease process of ALS.