Simultaneous loss of hamartin and tuberin from the cerebrum, kidney and heart with tuberous sclerosis

Tuberous sclerosis (TSC) is caused by a mutation in either the TSC1 or TSC2 gene. The clinical manifestations of mutations of the two genes are hardly distinguishable, for reasons as yet unknown. In this study, we examined the expression of the products of these genes, hamartin and tuberin, in control and TSC tissues. Western blotting disclosed that hamartin and tuberin are both abundant in the cerebral gray matter and that they have similar subcellular distributions and developmental patterns of expression. Immunohistochemical localizations of hamartin and tuberin were also similar, with high levels of expression being localized to the cerebral neurons and glial cells, renal uriniferous and collecting tubules, and cardiac muscles. In the cerebrum with TSC, both hamartin and tuberin were simultaneously reduced in the cortical tubers and subependymal giant cell astrocytomas, and from the normal-appearing cortex. The renal angiomyolipomas and cardiac rhabdomyomas also showed a loss of both the proteins. These results provide evidence for the co-localization and interaction of hamartin and tuberin in vivo, and suggest that a mutation in one TSC gene may secondarily affect the expression of the other in some TSC lesions.