Clinical variability in early speech-language development in females with Rett syndrome

Abstract

For clinicians treating children with developmental disorders, the paper by Marschik et al. has significant relevance.1 The study reported on pre-regression verbal development with a preserved speech variant and underscores what has been suspected regarding females with Rett syndrome. Those with preserved speech showed atypical development of vocalizations and communication as infants and young children, which contradicts the idea of ‘normal early development’. It is logical that mutations of the MECP-2 gene, which is expressed in the brain at different developmental periods, result in emerging abnormalities of speech and language development. Hence it is not surprising to find the subtle abnormalities of vocalizations and oral motor function, along with poor control of respiratory rhythm, that have been teased out diligently with hours of observations of videos provided by families. It would be useful for clinicians to request infant videos of the children in their care, so as to obtain added information on not only their communicative development but their gross movements2 which would add further to our understanding of their early abnormalities. Marschik et al. emphasize the early abnormalities in pre-linguistic communicative behaviours (intermittent and rapidly alternating character of expected and unexpected behaviours) and propose using this finding as a diagnostic marker. Perhaps it would be informative to focus on the poor oral motor control and involuntary movements affecting the orofacial muscles, which are more likely to be recognized. This may provide an opportunity to discuss with the family the lack of development of mature patterns of chewing and feeding, and how these movements affect speech articulation. The brief discussion regarding poor control of respiratory rhythm appears to be a crucial early finding which may alert the clinician to consider the diagnosis of Rett syndrome. It is true that infants and young children with Rett syndrome often remain undiagnosed. Marschik et al. suggest using subtle atypical vocalizations and behaviours as a diagnostic marker, but this recommendation places the clinicians on shaky ground. One is cognizant of the fact that raising the possibility of a serious neurological disorder with the family on clinically nebulous evidence is a difficult task for any clinician, who may then consider deferring the diagnosis until clinical findings are more obvious. Although a limited number of clinicians worldwide have experience in evaluating and following children with Rett syndrome, it is timely that we identify the specific types of dysfunctions. Einspieler et al.2 described abnormal general movements in females with Rett syndrome in the first 4 months and Marschik et al.’s earlier description of one female3,4 have obviously provided a foundation for more detailed study of abnormal motor movements. Although this study2 includes a very small sample of children with preserved speech who had Rett syndrome, it is commendable that the authors were able to access and study videos from six females ages 6–24 months. The six participants studied all had different mutations. These results are consistent with published data on the genotype-phenotype.5–8 Finally, as a challenge to clinicians, it would be important to document whether we can identify early abnormal oral motor dysfunction in children and how one would differentiate an oral motor disorder due to cerebral palsy versus Rett syndrome. I believe that the answer lies in the poor control of respiratory rhythm affecting abnormal inspiratory vocalizations.