Outcomes of Early Language Delay

Abstract

Genes are known to play an important role in causing specific language impairment, but it is unclear how far a similar etiology is implicated in transient language delay in early childhood. Two-year-old children with vocabulary scores below the 10th centile were selected from a cohort of over 2,800 same-sex twin pairs whose language was assessed by parental report at 2, 3, and 4 years of age. These children with early language delay (ELD) were divided into cases of transient and persistent language difficulties on the basis of outcome at 3 and 4 years. A DeFries-Fulker analysis (J. C. DeFries & D. W. Fulker, 1985) was used to compute group heritability (h 2 g ) of 2-year vocabulary delay separately for those with transient and persistent difficulties. When 3-year and 4-year language attainments were used to categorize outcomes, h 2 g was similar and modest (.25 or less) for both transient and persistent difficulties. However, when persistent difficulties were defined according to whether parents expressed concern about language at 3 years or according to whether a professional had been consulted about language difficulties at 4 years, heritability was significantly higher. For 289 children with no professional involvement at 4 years, heritability of 2-year vocabulary delay was close to zero, whereas for 134 children with professional involvement, a significant h 2 g of .41 ( SE =.127) was found. Early language delay appears largely environmental in origin for 2-year-olds whose parents do not go on to seek professional help.