Two populations of type I fibres in striated muscle from a case of neutral lipid storage disease.

Percutaneous needle biopsy of the vastus lateralis muscle was performed in a patient with a generalised accumulation of neutral triglyceride. Light microscopy revealed a type I fibre predominance, with neutral lipid droplets in both fibre types but larger and with a greater quantity of lipid per unit area in the type I fibre population. Within type I fibres there were at least two populations based on the lipid droplet size and total accumulated lipid per cell. These observations are discussed, and it is concluded that they support the hypothesis of metabolic differences within the type I fibre population with respect to the use of free fatty acids as a fuel source.