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November 1999

Learning Disabilities in Neurofibromatosis 1: Sizing Up the Brain

Arch Neurol. 1999;56(11):1322-1323. doi:10.1001/archneur.56.11.1322

NEUROFIBROMATOSIS 1 (NF1) is one of the most common genetic disorders affecting the nervous system.1 Individuals with NF1 manifest pigmentary abnormalities (café-au-lait macules, skin-fold freckling, and Lisch nodules) as well as benign and malignant tumors. Although NF1 commonly is regarded as an inherited predisposition to cancer syndrome, some of the most prominent features of this disorder are not attributable directly to tumor formation. In this regard, specific learning disabilities are observed in as many as 40% of children with NF1; 65% demonstrate impaired performance on at least one test of academic achievement.2 These children may have difficulties with spatial memory and learning, social and/or behavioral problems, or attention-deficit/hyperactivity disorder. The etiology for these learning disabilities in NF1 is unclear. Some investigators have suggested that the presence of hyperintense lesions on T2-weighted magnetic resonance imaging scans of the brain (unidentified bright objects [UBOs])may correlate with the presence of learning disabilities.3 There are even some data to imply that the presence of UBOs in particular regions of the brain (thalamus and hypothalamus) is more closely associated with learning problems in children with NF1.4 Clinicopathologic analysis of these lesions has demonstrated that UBOs represent abnormal areas of vacuolar change and not tumors or hamartomas.5 The presence of dysplastic astrogliosis surrounding some of these UBOs has pointed to abnormalities in white matter (astrocytes) as a possible cause of these lesions, and perhaps the learning disabilities. In support of this notion, morphometric studies of magnetic resonance imaging scans have shown increased white matter volumes in children with NF1, particularly in girls.6,7 One of these studies7 also reported a positive correlation between right hemisphere gray matter volume and performance on tests of visuospatial and visuomotor function.

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