Aetiologies of basic biliteracy difficulties in Hong Kong Chinese children: A latent profile analysis with twin data

The present study examined 1) basic biliteracy difficulty subtypes in Chinese (L1) and English (L2) Hong Kong Chinese children, 2) genetic-versus-environmental aetiologies for the subtypes, and 3) the moderating role of SES and school language use in the aetiologies. Four hundred fifty-six twin pairs (91.08 ± 13.20 months, 50% female) were assessed on Chinese and English word reading and spelling skills. Results of latent profile analysis identified four biliteracy profiles: 51.2% Chinese-dominant learners (CDL), 17.0% poor biliterate learners (PBL), 12.4% English-poor Chinese-dominant learners (EPCDL), and 19.4% English-dominant learners (EDL). Focusing on the difficulty profiles, results of familial resemblance showed that the additive genetic factor (55%) contributed more than the environmental factors to the probability of PBL, while the shared environmental factors (56%) contributed more than the genetic (25%) and unique environmental factors to the probability of EPCDL. Low SES was associated with a higher probability of PBL and EPCDL, and it exacerbated the genetic contribution to both difficulty profiles. The current findings suggest the influence of environmental factors underlying basic biliteracy difficulties, although we cannot rule out the possibility of high heritability, which appears to be the case for both L1 Chinese and L2 English.