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Energy toll of muscular dystrophy can play havoc with growth

Duchenne muscular dystrophy -- in young children and mice -- takes a significant protein and energy toll, often at the expense of growth in a critical period in the lives of the youngsters and infant animals, said a consortium of researchers from the USDA/ARS Children's Nutrition Research Center at Baylor College of Medicine and Texas Children's Hospital and at various research institutions in Australia. Their report appears in a recent issue of PLOS ONE.

Dr. Marta Fiorotto, associate professor of pediatrics – nutrition at Baylor and the USDA/ARS Children’s Nutrition Research Center at Baylor and Texas Children’s Hospital, and her colleagues studied juvenile mice and adult mice that have a genetic mutation that results in a disease similar to  human Duchenne muscular dystrophy. They compared them to normal mice of the same ages, measuring energy expenditure, food intake, spontaneous activity, body composition, whole body protein turnover and the rate at which they synthesized muscle proteins.

Processes have high energy cost

As in humans, the muscles of the muscular dystrophy mice lack a crucial protein called dystrophin. Their muscles are in a constant cycle of dying, regenerating and growing, processes which have a high energy cost.

Comparing the young mice to their normal counterparts, the scientists found that the young mice with the disease had significant muscle damage, expended more energy in the form of calories, and were constantly synthesizing muscle protein at a very high rate that was sufficient to increase the turnover of protein at the level of the whole body.

Increasing food intake and reducing activity did not make up for the energy and protein needs of the young muscular dystrophy mice, and as a result their growth was stunted.

Adult mice with the disorder also had similar higher energy requirements, protein synthesis and protein turnover rates than the normal adult mice. However, the intake of the diet they were provided was sufficient for their needs although they remained very lean. 

MD increases energy, protein requirements

“If the mice are not stressed, they seem to do fine,” she said. “However, if they run or they do not eat enough, the consequences for the muscles are much more severe even as adults.” 

"This shows that muscular dystrophy increases energy and protein requirements especially in the early stages of the disease, and if these are not met it could have significant consequences for the children and mice who suffer from it," said Fiorotto. “Improper nutrition may even interfere with possible treatments under research for the genetic disease. Special nutrition is probably needed.”

“The issue is more pressing in the youngsters -- both mice and children, because they are growing," she said. "They require more protein and energy for growth, and when muscles are constantly breaking down and repairing themselves, as in muscular dystrophy, the amounts provided in a normal diet may not be enough for everything."

There are very few reports in the scientific literature have looked at this age group in muscular dystrophy, she said. One recent survey of 2 to 12-year-old boys showed that a significant number of them are short for their age, she said. These results may provide an explanation for this.

The next question is whether and how to alter the diet in a way that will help. It is critical to also determine if the protein and energy metabolism of young boys with Duchenne muscular dystrophy is affected in the same way as in the mice. However, both of these goals will require funding.

The facilities at the Children's Nutrition Research Center were critical to helping them provide answers to many of their questions.

Others who took part in the study include: Hannah G. Radley-Crabb of Curtin University and the University of Western Australia in Perth, Australia; Miranda D. Grounds of the University of Western Australia; and Juan C. Marini, Horacio A. Sosa and Liliana I. Castillo of the Children’s Nutrition Research Center and Baylor.