For the genetic analyses, components were subdivided into reading, spelling, and phonological awareness. Reading, phonological awareness, and rapid naming latent traits showed heritability and some shared environment effects. Spelling showed a gene and and environment effect, while grammar had only an environment effect. Phonological awareness latent traits among the preschool children were based on several tasks: elision, blending, and matching of rhymes, beginning and final phonemes. Kindergarten measures were the same except the rhyme component. Environmental factors were not reliable for either group, and individual differences in phonological awareness was continuous from K to Gr. 1.
When analyzing relationships to print knowledge, results indicated that phonological awareness exerts genetic influence on later reading only through genes that it shares with print knowledge. Preschool print knowledge is about half as influenced by genes as is kindergarten reading, but the genetic correlation between these variables is higher (.79) than the genetic correlation between preschool phonological awareness and kindergarten reading (.54).
Although phonological awareness appears to be an inherited trait in this study, more so than print knowledge, only some of the genetic traits influence variability in reading and spelling at the end of kindergarten. One possible interpretation is that the preschool environmental varies for print familiarity, where children are encouraged to learn the alphabet, resulting in a lower estimate of heritability than would likely be the case in a less explicit environment. Genetic variation becomes more visible when children share a similar classroom environment, learning to associate letters and words with speech.
Research into effective practices that help those children with a genetic predisposition to develop later reading problems is warranted by this study, with particular emphasis on developing phoneme awareness in young children.