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Letter to the editor

We are concerned to correct misunderstandings concerning the Rett syndrome which may follow publication of Elian & Rudolf s paper (1). Frequent survival into the fourth decade, without deterioration in the post-regression level of mental handicap, has indicated that this should no longer be considered a progressive dementia. The author’s failure to find clear associations between paroxysmal abnormalities in breathing, blood gases and EEG in 16 Rett syndrome girls or to distinguish age-related changes may be due to the retrospective nature of their study and the absence of in vivo monitoring of the relevant parameters. In considering their subject, these authors have overlooked the findings of our studies presented in Dublin (IASSMD, 1988; 2, 3) with evidence from prospective continuous non-invasive monitoring of limb movement, breathing, transcutaneous p 0 2 and pC02, expired pC02, arterial oxygen saturation, EEG and ECG. In hyperventilating girls aged 5-10 years we demonstrated significant positive correlation (p = less than 0.01) between clearly defined paroxysms of movement and disturbed breathing (alternating hyperventilation and apnoea). We also found significant positive correlation between the EEG slowwave paroxysms characteristic of this age group and periods of quiet breathing with normal blood gases (p = less than 0.001). The paroxysmal EEG abnormality conspicuously diminished during hyperventilation. This hyperventilation reduced the levels of transcutaneous and expired pC02 which fell as low as 8 mm, often for prolonged periods. Efforts to sample expired C 0 2 may well miss this change since these children change from nose to mouth breathing during hyperventilation. We recorded epileptic seizures which appeared to be triggered by this hyperventilation. In addition to pC02 changes, significant hypoxaemia (less than 60%) occurred in some of the subsequent apnoeas. The constantly low pC02, regardless of respiratory activity described in the Elian Rudolf paper can only be explained as a failure of recording. After 10 years of age we found hyperventilation to fade while irregular apnoea with valsalva manoeuvers sometimes continued. At the same time the paroxysms of EEG slow wave and bursts of stereotyped movement lessened. In over 50 cases of Rett syndrome we have not found a normal EEG beyond 6 years of age (2-4). Without new evidence Drs Elian and Rudolf express support for the time-honoured view that the complex repetitive activities of the limbs, trunk, face and hands and respiratory muscles in Rett syndrome are chosen by the child. Our observations suggest rather that they happen to the child when she is alerted. These observations provide important insights into the underlying patho-physiology of Rett syndrome and carry important implications for management.