Carnitine deficiency is one of a group of metabolic muscle diseases that interferes with the processing of food (in this case, fats) for energy production.
If confined to muscles, this disease causes weakness in the hips, shoulders, and upper arms and legs. The neck and jaw muscles also may be weak. Heart muscle weakness may occur.
In more severe cases, in which other tissues are affected, symptoms can include low blood sugar, fatigue, vomiting, abdominal pain, growth retardation, low weight, enlarged liver and episodes of brain function abnormalities.
Carnitine deficiency may occur in response to a genetic mutation (gene defect) in the protein responsible for bringing carnitine into the cell (primary carnitine deficiency), or it may occur secondary to other metabolic diseases (secondary carnitine deficiency). See Causes/Inheritance  for more.
The disease has its onset from infancy to early adulthood and is slowly progressive.
Researchers on metabolic diseases of muscle are making progress on a number of fronts, including: