learning difficulties compared with those wi thout them. Family hist ory of reading diffi-
culties (dyslexia) and parental literacy skills predict literacy problems or specific learning
disorder in offspring, indicating the combin ed role of genetic and environmental factors.
There is high heritability for both reading ab ility and reading disability in alphabetic and
nonalphabetic languages, including high heritabi lity for most manifestations of learning abil-
ities and disabilities (e.g., heritability estimate  values greater than 0. 6). Covariation between
various manifestations of learning difficulties is high, suggesting that genes related to one
presentation are highly co rrelated with genes related to another manifestation.
Course modifiers. Marked problems with inattentive be havior in preschool years is pre-
dictive of later difficulties in reading and ma thematics (but not necessarily specific learn-
ing disorder) and nonresponse to  effective academic interventions. Delay or disorders in
speech or language, or impaired cognitive processing (e.g., phonological awareness,
working memory, rapid serial naming) in presch ool years, predicts la ter specific learning
disorder in reading and writ ten expression. Comorbidity wi th ADHD is predictive of
worse mental health outcome than that associ ated with specific learning disorder without
ADHD. Systematic, intensive, individualized instruction, using evidence-based interven-
tions, may improve or ameliorate the learning difficulties in some individuals or promote
the use of compensatory strategies in others , thereby mitigating the otherwise poor out-
comes.
Culture-Related Diagnostic Issues
Specific learning disorder oc curs across languages, cultures, races, and socioeconomic
conditions but may vary in its manifestation according to the nature of the spoken and
written symbol systems and cultural and educational practices. For example, the cognitive