MATHEMATICAL LEARNING DISABILITY IN GIRLS WITH TURNER SYNDROME: A CHALLENGE TO DEFINING MLD AND ITS SUBTYPES

Turner syndrome is a common disorder with a prevalence of 1 2,500 live female births. Although not associated with mental retardation, there is an increased risk of learning difficulties in this population. In particular, mathematical learning difficulties among girls with Turner syndrome are prevalent, significant, and persistent. As such, the study of mathematical performance in girls with Turner syndrome presents opportunities to advance our knowledge of mathematics ability, disability, and disability subtypes. Moreover, the Turner syndrome phenotype illustrates the challenges faced when defining mathematical learning disability (MLD) and characterizing MILD subtypes because the cognitive phenotype is aligned with several proposed MILD subtypes. There is some evidence linking MILD in Turner syndrome with spatial deficits, with executive dysfunction, and with deficient numerosity skills. Yet there is also conflicting evidence as to whether any of these explanations underlies MILD in Turner syndrome. Most mathematical difficulties in girls with Turner syndrome, as a group, occur on timed tests or on complex problems. On untimed tests, achievement test scores may be age appropriate. Therefore, the inclusion of MILD in the Turner syndrome cognitive phenotype reminds us that we cannot rule out MILD solely on the basis of performance on an untimed calculations subtest, and it poses a challenge to the widespread practice in which many researchers engage, that is, defining MILD on the basis of broad mathematics achievement test outcomes. (C) 2009 Wiley-Liss, Inc. Dev Disabil Res Rev 2009;15:35-44.