The clinical, electroencephalographic, and genetic findings are reported for three pairs of monozygotic twins who developed infantile spasms in their first year. In all three pairs, the spasms started on the same day in each member of the pair. Neither sequencing of the ARX and CDKL5 (alias STK9) genes nor array comparative genomic hybridization assessment revealed any abnormalities. The long-term outcome was poor in all twins, although with different severity in individual pairs. These findings suggest that genes other than those currently known likely play a role in predisposition to infantile spasms, and that genetic susceptibility is linked to a variable phenotypic expression, ranging from quite benign to very severe, in monozygotic twins with no other apparent risk factors.
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