Focal cortical dysplasia (FCD) type IIB is a malformation of cortical 
development characterized by presence of balloon cells. These cells share 
phenotypic features of giant cells found in tuberous sclerosis complex (TSC), 
but the relationship between FCD type IIB and TSC is not well established. TSC 
is an autosomal dominant disorder caused by mutation in either of two genes: 
TSC1, encoding hamartin, and TSC2, encoding tuberin. Both proteins form a 
complex inhibiting mTOR signalling pathway and thus regulate cell size and 
proliferation. In this study, tuberin and hamartin expression was evaluated 
under a confocal microscope in six cases of Taylor's balloon cell type FCD. 
Three patients met the clinical criteria for TSC. In three other patients, TSC 
was excluded based on a panel of clinical and radiological examinations. 
Additionally, two cases of FCD type I and 3 samples of normal brain tissue were 
used as a reference group. We found loss of tuberin and hamartin expression in 
FCD type IIB lesions from patients with TSC. In sporadic FCD type IIB cases, 
only a few tuberin and hamartin positive cells were detected in the white-grey 
matter junction and in deeper parts of the white matter. Cortical balloon cells 
showed loss of both tuberin and hamartin. In contrast, the expression of tuberin 
and hamartin in FCD type I samples was strong, similarly to normal brain tissue. 
In conclusion, loss of TSC1 and TSC2 products expression in balloon cells of 
both cortical dysplasia type IIB in TSC-related and sporadic patients suggests 
that FCD type IIB may represent the focal form of TSC.