T wo FMR 1 premutation cases without nuclear inclusions

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder that affects carriers of an FMR1 premutation. Premutation of 55-200 CGG repeats translates into increased FMR1 mRNA, inducing a toxic gain of function and/or translation of CGG repeats into a polyglycine-containing protein, FMRpolyG. Symptoms include ataxia and intention tremor. Pathology includes eosinophilic ubiquitin-positive intranuclear inclusions, which contain FMR1 mRNA and numerous proteins in neurons and astrocytes. It is unclear if all carriers with neurological symptoms present with FXTAS and/or inclusions. We report for the first time 2 carriers who had neurological symptoms but did not have FXTAS or intranuclear inclusions. All 28 postmortem premutation cases analyzed presented with intranuclear inclusions and were diagnosed with FXTAS, except 2 (Supplementary Fig. 1): an 82-year-old male premutation carrier with 66 CGG repeats (case 1) and an 87-year-old male premutation carrier with 65 CGG repeats (case 2). Case 1: At 77 he experienced memory loss and later developed shuffling gait and dementia. He needed a wheelchair and became severely demented and incontinent. He never had tremor. He had mild atrophic changes in the cerebral hemispheres, enlarged ventricles, and decreased size of the amygdala and hippocampus. Presented with diffuse arteriolosclerosis consistent with hypertension and diabetes, multifocal remote infarcts involving the cortex, hippocampus and basal ganglia, subacute hypoxic/ischemic changes, loss of purkinje cells, loss of the ependymal lining and subependymal gliosis, loss of pyramidal neurons in CA1, diffuse white matter gliosis, and increased Iba1positive microglia (Fig. 1). Clinical symptoms are compatible with the presence of severe brain vascular pathology, including multifocal infarctions that are indicative of a vascular cause of dementia. Case 2: He had a stroke at 76 and ataxia and mild cognitive deficits in his 80s. He never had tremor but developed motor coordination problems in his hands related to muscle weakness. He has 4 daughters who are all carriers. His niece had a son with mild FXS. This case was included in the article by Greco and colleagues in 2006. Microscopic findings included severe small-vessel disease (arteriolosclerosis) with hyalinization of intraparenchymal vessel walls, perivascular clearing, hemosiderin deposits, and microhemorrhages indicative of severe hypertension. Rare neurons contained Tau1 neurofibrillary tangles, with loss of cortical and CA1 neurons and of Purkinje cells. There was evidence of global hypoxic/ischemic changes, diffuse white-matter gliosis, focal loss of the ependymal lining and subependymal gliosis, and an increased number of Iba11 ramified microglia throughout the white matter (Fig. 1). Clinical symptoms are compatible with severe small-vessel disease (arteriolosclerosis) and acute intraparenchymal microhemorrhages. Both cases lacked intranuclear inclusions and had a low premutation range (65 and 66 CGGs). Although they had neurological symptoms, they did not have classical features of FXTAS. These cases demonstrate that not all individuals with the premutation develop intranuclear inclusions and FXTAS. The reason for the lack of inclusions is likely a low number of FMR1 CGG repetitions. However, we examined 2 additional cases with fewer than 70 repetitions (an 85-year-old woman with 63 CGGs and a 69-year-old man with 67 CGGs) who presented with inclusions in the cerebral cortex and cerebellum and were clinically categorized as FXTAS. We hypothesize that having a low CGG repeat number makes it less likely to develop FXTAS. However, other additional factors such as genetic or environmental factors may predispose a person with a low CGG repeat number to develop FXTAS.