Poster 26: Word Reading Compared to Demographics-Based Estimates of Premorbid IQ in Early Huntington Disease

Background Irregular word pronunciation is a common method of estimating premorbid intellect, because it is resistant to neurological insult/deterioration. However, emerging research suggests word reading ability declines in some neurodegenerative diseases, resulting in an underestimation of premorbid IQ. Misrepresentation of predisease intellect may affect clinical diagnosis and confound the selection of participants for clinical trials. An alternative method is the use of a demographically-based equation to estimate intelligence. Aim To compare the WRAT Reading Subtest (a pronunciation measure) and the Barona Index (a demographically-based regression equation) as estimates of premorbid IQ in individuals with mild to moderate Huntington disease (HD). Method Using participants (n = 73) pooled from two clinical trials and an outpatient HD clinic, we examined WRAT and Barona standard scores and their discrepancy, along with demographic and clinical characteristics. Results Mean age was 47.6 years (SD = 11.7), total functional capacity (TFC) was 9.6 (SD = 3.0), and total motor score (TMS) was 32.7 (SD = 15.8). Average WRAT standard score was 91.9 (SD = 11.9), while Barona was 108.0 (SD = 7.2), with a mean discrepancy of 16.1 (SD = 10.7; range –42.3 to +6.3). Although true premorbid IQ is unknown, this sample overrepresented higher levels of education (i.e., ∼22% of the sample had 16+ years, while ∼8% had p Discussion The WRAT produced premorbid IQ estimates lower than the Barona for 93% of participants and was below expectations given the sample's mean education. Unlike the Barona, the WRAT was associated with impaired motor functioning, suggesting that it may decline with disease. Therefore, the Barona Index may be a more appropriate measure of premorbid intelligence in persons with HD and should be considered for subject selection in clinical trials and clinical evaluation.