[Membranous lipodystrophy of the bone]

Membranous lipodystrophy is a rare disease in which cyst-like lesions of fat occur in subcutaneous and other sites including bone marrow, together with sudanophilic leukoencephalopathy. The disease has been reported mostly in Finland and in Japan, with sporadic cases from USA, Belgium, Italy, and France. The cyst-like lesions of limb bones progress in early adult life, usually followed by neurological disorders including convulsions and presenile dementia. Histologically, the fat cells of the bone marrow, synovial membrane, and other sites, are replaced by a convoluted, hyaline, eosinophilic membrane that surrounds a large space. The histochemical and ultrastructural characteristics of the membranes are described. In the brain, atrophy of the subcortical white matter of the frontal and temporal lobes with marked astrocytosis and fibrillary gliosis, and a slight or moderate degeneration of myelin sheaths, are the most prominent changes. Genetic studies of the disease have been reported, revealing an autosomal recessive gene, explaining both its sporadic and familial occurrence, with mutations involving the gene encoding a transmembrane protein, key activating signal transduction element in NK cells (TYROBP). The pathogenesis of membranocystic changes is still unknown: result of a metabolic disorder or circulatory disturbances.