Clinical and Neuropathologic Findings in a Woman With the FMR1 Premutation and Multiple Sclerosis

Multiplesclerosis(MS), the most common demyelinating disease of the central nervous system (CNS), affects more than 350 000 people in the United States and an estimated 2 million people worldwide; CNS demyelination and varying degrees of axonal injury and inflammation are essential features in established cases. The consistent presence of axonal dysfunction has furthered an understanding of sustained disability and regenerative failure in those with MS.1 Premutation alleles (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene are common (1 per 100-300 females and 1 per 300-800 males); toxic effects caused by the excess amount of premutation FMR1 messenger RNA (mRNA) leads to the adult-onset neurologic disorder fragile X–associated tremor/ataxia syndrome (FXTAS).2 The penetrance of FXTAS in male carriers throughout 50 years, ascertained through families with a fragile X syndrome proband, is approximately 40%; its penetrance in female carriers is lower (approximately 5%-10%).2,3 The pathologic features of FXTAS include intranuclear inclusions in neurons and astrocytes throughout the brain and brainstem, astrocyte activation, axonal retraction bulbs, axonal loss, and myelin loss.4,5 The inclusions contain αB-crystallin, MBP, lamin A/C isoforms, and numerous other proteins.5 The toxic effects of FMR1 mRNA also result in the disruption of nuclear lamin A/C architecture and formation of perinuclear αB-crystallin aggregates in cultured neural cells.6