Neuron-like cells in culture of tuberous sclerosis tissue

Human XPMC2H: cDNA cloning, mapping to 9q34, genomic structure, and evaluation as TSC1

XPMC2 is a Xenopus gene identified on the basis of its ability to correct a mitotic defect in fission yeast. Here we report the identification of cDNA clones for human XPMC2H, its mapping to the tuberous sclerosis gene TSC1 region on 9q34, determination of genomic structure, and identification of several coding region polymorphisms. The predicted protein has strong sequence similarity to the Xenopus gene. Through SSCP and heteroduplex analysis of genomic DNA, we found two intragenic polymorphisms but no evidence for significant mutations in patients with tuberous sclerosis in this gene.

Evidence of abnormal differentiation in giant cells of tuberous sclerosis

To characterize the giant cells in tuberous sclerosis, we examined immunoreactivity for nestin, vimentin, microtubule-associated protein 1B (MAP1B), MAP2, neurofilament, and glial fibrillary acidic protein (GFAP) in cortical tubers detected in brain specimens from 6 patients with tuberous sclerosis who had undergone surgical resection for treatment of intractable epilepsy. Giant cells with a neuronal appearance, "neuron-like giant cells," had a round centrally-placed nucleus with a single, prominent nucleolus, and Nissl substance was commonly present in cortex. These neuron-like giant cells demonstrated consistently strong immunoreactivity for neurofilament and MAP1B and occasional immunopositivity for nestin and vimentin and were rarely positive for GFAP. "Indeterminate giant cells," characterized by abundant cytoplasm, an absence of Nissl substance, and one or more eccentric nuclei, demonstrated consistent immunoreactivity for nestin, vimentin, and MAP1B and were rarely positive for neurofilament, but more than half displayed immunoreactivity for GFAP. These observations suggest that the indeterminate giant cells exhibit limited neuronal and inconsistent astroglial characteristics, implying aberrant cellular differentiation in tuberous sclerosis.

Tuber and subependymal giant cell astrocytoma associated with tuberous sclerosis: an immunohistochemical, ultrastructural, and immunoelectron and microscopic study

The cellular nature of the giant eosinophilic cells of tuber and of the cells comprising subependymal giant cell astrocytoma (SEGA) in tuberous sclerosis (TS) remains unclear. To assess the characteristics of these lesions, 13 tubers and 6 SEGA were immunohistochemically studied with glial and neuron-associated antigens. In addition to conventional ultrastructure, 6 tubers and 8 SEGA were subjected to immunoelectron microscopic study for glial fibrillary acidic protein (GFAP) and somatostatin. Eosinophilic giant cells of tubers were positive for vimentin (100%), GFAP (77%) and S-100 protein (92%); such cells were also found to a various extent to be reactive for neuron-associated antigens, including neurofilament (NF) proteins (38%) or class III beta-tubulin (77%). SEGA also showed variable immunoreactivity for GFAP (50%) or for S-100 protein (100%); NF epitopes, class III beta-tubulin, and calbindin 28-kD were expressed in 2 (33%), 5 (83%) and 4 (67%) cases, respectively. Cytoplasmic staining for somatostatin (50%), met-enkephalin (50%), 5-hydroxytryptamine (33%), beta-endorphin (33%) and neuropeptide Y (17%) was noted in SEGA, but not in tubers. Ultrastructurally, the giant cells of tubers and the cells of SEGA contained numerous intermediate filaments, frequent lysosomes and occasional rectangular or rhomboid membrane-bound crystalloids exhibiting lamellar periodicity and structural transition to lysosomes. Some SEGA cells showed features suggestive of neuronal differentiation, including stacks of rough endoplasmic reticulum, occasional microtubules and a few dense-core granules. Furthermore, in one case of tuber, a process of a single large cell was seen to be engaged in synapse formation. Intermediate filaments within a few cells of both lesions were decorated by gold particle-labeled GFAP antiserum. Within the tumor cells of SEGA, irregular, non-membrane-bound, electron-lucent areas often contained somatostatin-immunoreactive particles, whereas the latter could not be detected in tuber. The present study provides further evidence of divergent glioneuronal differentiation, both in the giant cells of tubers and the cells of SEGA. The findings of similar cells at different sites, including the subependymal zone, white matter ("heterotopias"), and cortex indirectly supports the idea that these lesions of TS result from a migration abnormality.

Clinical, neuropathological and genetic aspects of the tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome in which patients develop hamartomatous lesions in the nervous system and a host of other organs. While considerable experience has been gained in defining the clinical spectrum of TSC, a number of nosological questions remain. Neuropathological studies have continued to refine our knowledge of the nervous system abnormalities that characterize TSC. Molecular genetic studies have implicated two chromosomal regions in the genesis of TSC, one on chromosome 9q and the other on chromosome 16p. The chromosome 16p gene, designated TSC2, has been cloned, although its function remains speculative. The identification of the TSC1 gene on chromosome 9q, along with functional studies and mutational analyses of both TSC genes, will likely provide fascinating insights into the pathogenesis of TSC.

Renal involvement in tuberous sclerosis complex: a retrospective survey

In a retrospective survey performed in Germany and Switzerland, 207 patients (ranging in age from newborn to 70 years) were evaluated in order to establish the frequency, prognosis and diagnostic awareness of kidney involvement in the tuberous sclerosis complex. Renal manifestations were observed in 48% of patients: renal cysts (33 patients), renal angiomyolipoma (AML) (30 patients), a combination of both (8 patients), renal cell carcinoma (3 patients), life-threatening events such as haemorrhage (4 patients), hypertensive crisis (2 patients) and chronic renal failure (10 patients) were also documented. The diagnostic imaging techniques of ultrasonography, intravenous urography, computed tomography and magnetic resonance imaging (MRI) are important but do not always yield definitive information. Differentiation between AML and cysts can be achieved using special MRI techniques (RARE). The potential for renal involvement should be monitored in all patients with the tuberous sclerosis complex.

The neuropathology of tuberous sclerosis

Tuberous sclerosis, an autosomal dominant disorder associated with hamartomas in multiple organs, prominently affects the central nervous system; principle lesions include subependymal nodules and giant cell astrocytomas, white matter heterotopias, and cortical tubers. Histologic, immunocytochemical, and ultrastructural features of these processes suggest they have their basis in abnormal cell migration and differentiation. Aberrant expression of cystoskeletal proteins appears to be common to the multisystem hamartomas of this disorder and may, in part, underlie their pathogenesis.