Cognitive phenotype of mathematical learning disabilities: What can we learn from siblings? Annemie Desoete a,b, *, Magda Praet a , Daisy Titeca a , Annelies Ceulemans a a Ghent University, Department of Experimental Clinical and Health Psychology, Henri Dunantlaan 2, B-9000 Ghent, Belgium b Artevelde University College, Ghent, Belgium 1. Introduction Mathematical literacy is important in our society (e.g., Vanmeirhaeghe, 2012). Most practitioners and researchers currently report a prevalence of mathematical learning disabilities (MLD) between 3 and 14% of children (Barbaresi, Katuskic, Colligan, Weaver, & Jacobsen, 2005; Geary, 2011; Geary, Hoard, Nugent, & Bailey, 2011; Shalev, Manor, & Gross-Tsur, 2005). The prevalence of MLD in siblings even ranges from 40 to 64% (Shalev et al., 2001). The comorbidity between MLD and reading disabilities is estimated between 30% and 50% (Shalev, Auerbach, Manor, & Gross-Tsur, 2000), Given that MLD is associated with cost to society, family and the individual person, it is important to better understand what causes MLD so that treatments can be developed and targeted at the underlying causes. In some disorders the study of the phenotypes helps to speed up the understanding of the disorder (e.g., Cinnamon Bidwell, Willcutt, DeFries, & Pennington, 2007). Cognitive phenotypes are impaired processes commonly affected in individuals and their siblings, relatively unique to the disorder, and comparatively uncommon in the normal population. Cognitive phenotypes have to be sensitive (affected in individuals and their siblings) and specific (relatively unique to the disorder and uncommon in the normal population). Research in Developmental Disabilities 34 (2013) 404–412 A R T I C L E I N F O Article history: Received 15 July 2012 Accepted 28 August 2012 Available online 26 September 2012 Keywords: Mathematical learning disability (MLD) Cognitive phenotype Number line estimation Siblings Magnitudes Early literacy Early numeracy Kindergarten A B S T R A C T The sensitivity of number sense as cognitive phenotype for mathematical learning disabilities (MLD) was assessed in siblings of children with MLD (n = 9) and age matched children without family members with MLD (n = 63). A number line estimation paradigm was used as a measure of children’s early number sense. In line with the triple code model of Dehaene (1992), three different presentation formats were presented. The results of the study confirmed that number line estimation was related to early arithmetic achievement in kindergarten. In addition siblings were less proficient in number line placements compared to non-siblings, with a larger effect size for symbolic and especially number word estimation compared to the non-symbolic results. Siblings also differed from non- siblings on procedural and conceptual counting skills and logical thinking in kindergarten. Moreover MLD had a familial aggregation, since about three out of five sibling girls had clinical scores on an Early Numeracy Test in kindergarten, pointing to a risk to develop MLD themselves. Implications of the study to our understanding of MLD are discussed. ß 2012 Elsevier Ltd. All rights reserved. * Corresponding author at: Department of Experimental Clinical and Health Psychology, Developmental Disorders, Henri Dunantlaan 2, 9000 Ghent, Belgium. Fax: +32 9 264 64 89. E-mail addresses: annemie.desoete@arteveldehs.be, Annemie.Desoete@Ugent.be (A. Desoete). Contents lists available at SciVerse ScienceDirect Research in Developmental Disabilities 0891-4222/$ – see front matter ß 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ridd.2012.08.022