Context: The molecular mechanisms by which triglycerides in lipid droplets (LDs) are synthesized, stored and degraded need to be elucidated.

Objective: The objectives were to report siblings with neutral lipid storage disease with myopathy (NLSDM) with a novel mutation of adipose triglyceride lipase (ATGL) and to determine whether the C-terminal part of ATGL containing the hydrophobic region plays a role in the interaction with LDs.

Design and Patients: Skin fibroblasts, peripheral blood leukocytes were obtained from NLSDM patients. In vitro experiments were performed with fibroblasts and COS7 cells.

Main Outcome Measures: Transfection studies were used to assess the effects of various recombinant ATGL proteins on lipase activities and lipid contents. Fluorescence microscopy were used for determination of intracellular distribution of ATGL proteins.

Results: The direct sequence of ATGL cDNA reveals that a patient is a homozygote for the four base-pair deletion, leading to a premature stop codon and causes the lack of the C-terminus of the protein including the hydrophobic domain. Overexpressed control ATGL in NLSDM fibroblasts was found around the rims of LDs and caused significantly reduced cellular lipid accumulation. In contrast, NLSDM ATGL was homogeneously located in the cytoplasm despite the presence of LDs and had almost no effect on LD degradation in spite of its similar lipase activity. A series of C-terminal truncated ATGLs without the intact hydrophobic domain failed to localize around and to degrade LDs.

Conclusions: These findings indicate that the domain including the hydrophobic region of ATGL was essential for association with LDs.