Treatment of infantile spasms in tuberous sclerosis complex: dismal outcomes but future hope?

Safety and efficacy of vigabatrin for the treatment of infantile spasms

In 2009, vigabatrin became the first FDA approved medication for the treatment of infantile spasms in the United States. There are few well-designed prospective studies comparing the drug to placebo or other modalities used in the treatment of infantile spasms. The available data have demonstrated that vigabatrin is efficacious in the treatment of infantile spasms regardless of underlying etiology, but that it is particularly beneficial in patients with a diagnosis of tuberous sclerosis. Adrenocorticotropic hormone (ACTH), the only other medication with robust efficacy data, has been used as first line therapy for infantile spasms associated with other etiologies, and in general controls spasms sooner than vigabatrin, though relapse is common with both therapies. Vigabatrin is generally well tolerated. However, use has been associated with permanent loss of peripheral vision in some patients. In children with tuberous sclerosis, vigabatrin should be considered as initial therapy for infantile spasms. It is a viable alternative for patients with suboptimal response, contraindications or intolerance to ACTH.

Neuronal and glia abnormalities in Tsc1-deficient forebrain and partial rescue by rapamycin

Tuberous Sclerosis Complex (TSC) is a multiorgan genetic disease that prominently features brain malformations (tubers) with many patients suffering from epilepsy and autism. These malformations typically exhibit neuronal as well as glial cell abnormalities and likely underlie much of the neurological morbidity seen in TSC. Tuber pathogenesis remains poorly understood though upregulation of the mTORC1 signaling pathway in TSC has been consistently demonstrated. Here we address abnormal brain development in TSC by inactivating the mouse Tsc1 gene in embryonic neural progenitor cells. This strategy permits evaluation of the role of the Tsc1 gene in both neuronal as well as glial cell lineages. Tsc1(Emx1-Cre) conditional knockout (CKO) animals die by 25 days of life. Their brains have increased size and contain prominent large cells within the cerebral cortex that have greatly increased mTORC1 signaling and decreased mTORC2 signaling. Severe defects of cortical lamination, enlarged dysmorphic astrocytes and decreased myelination were also found. Tsc1(Emx1-Cre) CKO mice were then treated with rapamycin to see if the premature death and brain abnormalities can be rescued. Postnatal rapamycin treatment completely prevented premature death and largely reversed the glia pathology but not abnormal neuronal lamination. These findings support a model that loss of function of the TSC genes in embryonic neural progenitor cells causes cortical malformations in patients with TSC. The dramatic effect of rapamycin suggests that even with extensive multi-lineage abnormalities, a postnatal therapeutic window may exist for patients with TSC.