A validated WAIS-IV short-form to estimate intellectual functioning in myotonic dystrophy type 1

Currently, no rapid and specific instrument is available to briefly estimate intelligence in patients with myotonic dystrophy type 1 (DM1), a multisystemic disease that involves the CNS and is associated with cognitive deficits and low intellectual functioning. This study aimed to develop a DM1-specific and valid short-form of the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) to estimate intellectual functioning in this population. Thirty non-congenital DM1 patients (10 female; mean age=46.77; SD= 9.76) were assessed with the WAIS-IV. Data were analyzed following two independent strategies: A) multiple linear regression with the aim of maintaining the scale's factorial structure; and B) correlational analyses between scores on all WAIS-IV subtests and Full-Scale IQ (FSIQ). Validity of the resulting short-forms was also analyzed. Three short-forms were developed: Proposal A from strategy A (Vocabulary, Block Design, Arithmetic and Symbol Search), Proposal B1 (Vocabulary, Block Design, Digit Span and Visual Puzzles) and Proposal B2 (Vocabulary and Block Design), from strategy B. All three short-forms showed a strong and significant correlation with the FSIQ and were considered psychometrically acceptable. Arguments in favor of Proposal B1 are discussed. Assessing FSIQ with these short-forms will be useful for avoiding long assessment procedures in a population characterized by high fatigability.