Genetic and environmental risks for specific language impairment in children

Specific language impairment (SLI) is the term used to refer to unexplained difficulties in language acquisition in children. Over the past decade, th ere has been rapid growth of evidence indicating that genes play an importa nt part in the aetiology of SLI. However, further progress in elucidating t he role of genes in causing SLI is limited by our lack of understanding of the phenotype. Studies to date have been hampered by the fact that we do no t know whether SLI should be treated as a discrete disorder or a continuous variable, let alone which measures should be used to identify cases, or ho w many subtypes there are. Recent research suggests that theoretically moti vated measures of underlying processes may be better than conventional clin ical diagnoses for identifying aetiologically distinct types of language im pairment. There has been a tendency for researchers to embrace parsimony an d look for a single cause of SLI-or in any event, to identify different sub types, each with a different single cause. Research is reviewed that sugges ts that may not be a fruitful approach to SLI, and that an approach in term s of multiple risk and protective factors, which is widely adopted in medic ine, is more realistic.