Resounding failure to replicate links between developmental language disorder and cerebral lateralisation

Background. It has been suggested that failure to establish cerebral lateralisation
may be related to developmental language disorder (DLD). There has been weak
support for any link with handedness, but more consistent reports of associations with
functional brain lateralisation for language. The consistency of lateralisation across
different functions may also be important. We aimed to replicate previous findings
of an association between DLD and reduced laterality on a quantitative measure of
hand preference (reaching across the midline) and on language laterality assessed using
functional transcranial Doppler ultrasound (fTCD).
Methods. From a sample of twin children aged from 6;0 to 11;11 years, we identified
107 cases of DLD and 156 typically-developing comparison cases for whom we had
useable data from fTCD yielding a laterality index (LI) for language function during an
animation description task. Handedness data were also available for these children.
Results. Indices of handedness and language laterality for this twin sample were
similar to those previously reported for single-born children. There were no differences
between the DLD and TD groups on measures of handedness or language lateralisation,
or on a categorical measure of consistency of left hemisphere dominance. Contrary to
prediction, there was a greater incidence of right lateralisation for language in the TD
group (19.90%) than the DLD group (9.30%), confirming that atypical laterality is not
inconsistent with typical language development. We also failed to replicate associations
between language laterality and language test scores.
Discussion and Conclusions. Given the large sample studied here and the range of
measures, we suggest that previous reports of atypical manual or language lateralisation
in DLD may have been false positives.