Elsevier

Journal of Communication Disorders

Volume 35, Issue 6, November–December 2002, Pages 501-531
Journal of Communication Disorders

Anatomical risk factors that distinguish dyslexia from SLI predict reading skill in normal children

https://doi.org/10.1016/S0021-9924(02)00120-XGet rights and content

Abstract

These studies investigated whether anatomical measures could separate phonologically-based reading disability (PD) from nonphonologically-based learning disabilities such as specific language impairment (SLI). In a previous study, four brain measures (cerebral asymmetry, summed planum temporale and parietale asymmetry, anterior cerebellar asymmetry, and a duplicated left Heschl’s gyrus) distinguished a group of PD adults from reading disabled adults without specific phonological deficits (URD). Study 1 found that these measures did not distinguish 14 reading disabled children from 21 children with SLI. Instead, differences were found in cerebral volume, planum temporale asymmetry, and the size of a single left Heschl’s gyrus. Study 2 demonstrated that including all seven measures in a discriminant analysis separated the adults and children into two groups: one with 100% of the PD adults and 75% of the reading disabled children and the other with 72% of the SLI children and 75% of the URD adults. Study 3 demonstrated that an anatomical risk factor index (ARF7) generated from the discriminant function with seven brain measures predicted reading in normal children. Children with ARF7 near 0 (normal anatomy) had superior verbal ability and phonological decoding scores that improved with age. Normal children with negative ARF7 (the relatively small symmetrical structures that characterize SLI) had deficits in verbal ability. Children with positive ARF7 (the asymmetrical structures that characterize PD) had phonological decoding scores that decreased with age. These results suggest that PD and SLI are qualitatively different disorders associated with anatomical deviations in opposite directions from the population mean.

Learning outcomes

As a result of this activity, the participant will be able to: (1) distinguish the neuroanatomical features that characterize PD and SLI; (2) recognize that PD is associated with large asymmetrical brain structures while SLI is associated with smaller symmetrical brain structures; (3) understand that children with moderate sized brains and whose anatomy is intermediate between symmetry and extreme asymmetry have an enhanced probability of developing good verbal ability; (4) understand that reading disabilities depend on the interaction of neurodevelopment and the environment

Section snippets

Reading disability (RD)

Fourteen RD children were identified in two longitudinal studies of reading development conducted between 1991 and 1998. Nine children came from LONG1, a study in which 149 children representative of the socioeconomic distribution

Anatomical subtype and normal reading development

In view of the many factors that affect reading scores in a heterogeneous sample of children, the fact that a purely anatomical classification predicted diagnosis is notable. The analysis of normal children was a prospective validation of the predictive ability of the brain measures in a separate population. The analysis showed that normal children with ASY subtypes, like ASY adults with PD, had specific weaknesses in phonological decoding, weaknesses that increased with age. Children with SS

Acknowledgements

The authors are very grateful to the parents and children who participated in these experiments; to Laurie Gauger, Cynthia Puranik, Nicholas Benson, Bryan Mahoney, Angie Bollich, Cecile Mohr, Alan Freeman, and Wayne King for recruiting, testing and measuring brain anatomy, to John Kranzler and Thomas Oakland for consultation, to Bill Bell for excellent assistance in scanning, and to Wendy Swearingen, Marina Santarpia, Jim Weaver, Brandi Griffin, Jon Akers, David Parks, Dan Bradley and Sarah

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