Alison M. Kerr

Characterisation of breathing and associated central autonomic dysfunction in the Rett disorder

AIM To investigate breathing rhythm and brain stem autonomic control in patients with Rett disorder. SETTING Two university teaching hospitals in the United Kingdom and the Rett Centre, Sweden. PATIENTS 56 female patients with Rett disorder, aged 2–35 years; 11 controls aged 5–28 years. DESIGN One hour recordings of breathing movement, blood pressure, ECG R-R interval, heart rate, transcutaneous blood gases, cardiac vagal tone, and cardiac sensitivity to baroreflex measured on-line with synchronous EEG and video. Breathing rhythms were analysed in 47 cases. RESULTS Respiratory rhythm was normal during sleep and abnormal in the waking state. Forced and apneustic breathing were prominent among 5–10 year olds, and Valsalva breathing in the over 18 year olds, who were also most likely to breathe normally. Inadequate breathing peaked among 10–18 year olds. Inadequate and exaggerated breathing was associated with vacant spells. Resting cardiac vagal tone and cardiac sensitivity to baroreflex were reduced. CONCLUSIONS Labile respiratory rhythms and poor integrative inhibition in Rett disorder suggest brain immaturity. Linking this to an early monoaminergic defect suggests possible targets for the MECP2 gene in clinical intervention. Exaggerated and inadequate autonomic responses may contribute to sudden death.

Guidelines for reporting clinical features in cases with MECP2 mutations

An international group recommends that papers relating phenotypes to genotypes involving mutations in the X chromosome gene MECP2 should provide a minimum data set reporting the range of disturbances frequently encountered in Rett Syndrome. A simple scoring system is suggested which will facilitate comparison among the various clinical profiles. Features are described which should prompt screening for MECP2 mutations.

Is the Early Development of Girls with Rett Disorder Really Normal

An apparently normal early development was one of the initial criteria for classical Rett syndrome. However, several investigators considered Rett syndrome to be a developmental disorder manifesting very soon after birth. Videos of 22 Rett cases were assessed carefully for movements, posture, and behavior during the first 6 mo of life. All signs that deviated from the normal standard were recorded meticulously. Special attention was paid to the face, the hands, and body movements. A detailed analysis clearly demonstrated an abnormal quality of general movements (100%), tongue protrusion (62%), postural stiffness (58%), asymmetric eye opening and closing (56%), abnormal finger movements (52%), hand stereotypies (42%), bursts of abnormal facial expressions (42%), bizarre smile (32%), tremor (28%), and stereotyped body movements (15%). Our study is the first to apply specific standardized measures of early spontaneous movements to Rett infants, proving conclusively that the disorder is manifested within the first months of life. Although not necessarily specific, the signs that we have observed will be of value in alerting clinicians to the possibility of the diagnosis at an early stage, when intervention is likely to be most effective.

Gross rearrangements of the MECP2 gene are found in both classical and atypical Rett syndrome patients

MECP2 mutations are identifiable in ∼80% of classic Rett syndrome (RTT), but less frequently in atypical RTT. We recruited 110 patients who fulfilled the diagnostic criteria for Rett syndrome and were referred to Cardiff for molecular analysis, but in whom an MECP2 mutation was not identifiable. Dosage analysis of MECP2 was carried out using multiplex ligation dependent probe amplification or quantitative fluorescent PCR. Large deletions were identified in 37.8% (14/37) of classic and 7.5% (4/53) of atypical RTT patients. Most large deletions contained a breakpoint in the deletion prone region of exon 4. The clinical phenotype was ascertained in all 18 of the deleted cases and in four further cases with large deletions identified in Goettingen. Five patients with large deletions had additional congenital anomalies, which was significantly more than in RTT patients with other MECP2 mutations (2/193; p<0.0001). Quantitative analysis should be included in molecular diagnostic strategies in both classic and atypical RTT.

Acetazolamide in prevention of acute mountain sickness: a double-blind controlled cross-over study.

Twenty-four amateur climbers took part in a double-blind controlled cross-over trial of acetazolamide versus placebo for the prevention of acute mountain sickness. They climbed Kilimanjaro (5895 m) and Mt Kenya (5186 m) in three weeks with five rest days between ascents. The severity of acute mountain sickness was gauged by a score derived from symptoms recorded daily by each subject. On kilimanjaro those taking acetazolamide reached a higher altitude (11 v 4 reached the summit) and had a lower symptom score than those taking placebo (mean 4.8 v 14.3). Those who had taken acetazolamide on Kilimanjaro maintained their low symptom scores while taking placebo on Mt Kenya (mean score 1.9), whereas those who had taken placebo on Kilimanjaro experienced a pronounced improvement when they took acetazolamide on Mt Kenya (mean score 2.5). Acute mountain sickness prevented one subject for completing either ascent. Acetazolamide was acceptable to 23 of the 24 subjects. Acetazolamide is recommended as an acceptable and effective prophylactic for acute mountain sickness.

Recent insights into hyperventilation from the study of Rett syndrome

The medical literature presents two major groups of disorder in which hyperventilation is a presenting feature. Disorders of mood, notably panic disorder, and disorders of brain stem function—developmental, vascular, traumatic, toxic, metabolic, degenerative or neoplastic. References to the underlying brain morphology leading to these conditions are few and imprecise, perhaps reflecting the inaccessibility of the brain stem to clinical medicine and the complexity of the neural basis of respiratory control. Even in Joubert’s syndrome, where hyperventilation is a major feature, hypoplasia of the cerebellar vermis and cyst of the fourth ventricle have been described but the exact pathophysiology is unclear.1 The clinical medical literature gives more space to discussing the effects of hyperventilation, including the well known respiratory alkalosis with reduction in plasma ionised calcium, tingling sensations, tetany, induction of epileptic seizures, and induction of interictal epileptogenic activities seen on the electroencephalogram (EEG). In healthy children, especially girls, voluntary hyperventilation produces slow EEG waves, usually generalised over the cerebral cortex. Hyperventilation reduces oxygen delivery to the brain,2 and cardiac repolarisation abnormalities including ST depression and T wave inversion have been described.3 From its delineation in 1937 to the 1980s, the “hyperventilation syndrome” was held responsible for much of the symptomatology of panic disorder4; however, with increased accuracy of measurements, this notion was replaced by the view that autonomic instability underlies both hyperventilation and panic disorder.5 Although there is a clear association between panic and hyperventilation, the neurological basis for this is still unresolved. Hyperventilation or overbreathing is variously defined, according to the measures available and familiar to each scientific discipline. There is agreement that the breathing exercise must ventilate the lungs in excess of metabolic requirements at that particular point in time and thus induce measurable changes, usually a reduction in arterial or alveolar …

Dimensional phenotypic analysis and functional categorisation of mutations reveal novel genotype-phenotype associations in Rett syndrome.

We aimed to improve the understanding of genotype–phenotype correlations in Rett syndrome (RS) by adopting a novel approach to categorising phenotypic dimensions – separating typicality of presentation, outcome severity and age of onset – and by classifying MECP2 mutations strictly by predicted functional attributes. MECP2 mutation screening results were available on 190 patients with a clinical diagnosis of RS (140 cases with classic RS, 50 with atypical RS). 135 cases had identified mutations. Of the 140 patients, 116 with classic RS (82.9%) had an identified mutation compared with 19 of 50 patients (38%) with an atypical presentation. Cases with early onset of regression and seizures, and those with clinical features that might indicate alternative aetiologies, were less likely to have mutations. Individuals with late truncating mutations had a less typical presentation than cases with missense and early truncating mutations, presumably reflecting greater residual function of MECP2 protein. Individuals with early truncating mutations had a more severe outcome than cases with missense and late truncating mutations. These findings held when restricting the analysis to cases over 15 years of age and classic cases only. Previous findings of variation in severity among the common mutations were confirmed. The approach to phenotypic and genotypic classification adopted here allowed us to identify genotype–phenotype associations in RS that may aid our understanding of pathogenesis and also contribute to clinical knowledge on the impact of different types of mutations.

Results of surgery for scoliosis in Rett syndrome.

The British Isles Survey for Rett Syndrome stores longitudinal health data from clinical examinations and postal questionnaires to monitor health and severity in Rett syndrome, including the presence and severity of scoliosis and the effects of corrective surgery. Scoliosis is rarely present at birth (3% before regression) but usually appears by 25 years (87%). The degree tends to increase with growth and by 16 to 20 years, 43% (75 of 173) of cases with classic Rett syndrome reported severe or operated scoliosis. Surgical correction was reported in 91 classic cases. Following initial postoperative recovery, families considered that the operation had improved general well-being for 84% of individuals (42 of 50 classic cases with postoperative health reports). Thirteen of 50 patients walked independently before surgery, and 12 patients did so following surgery; 2 stopped walking, and 1 who had not walked began to do so. Scoliosis surgery usually benefited sitting posture (82% better, 10% worse), chest episodes (52% better, 6% worse), and digestion of food (42% better, 6% worse). However, toilet function was improved in only 10% and deteriorated in 20%. Families reported short-term problems at operation in 48% (24 of 50) and minor recurrence of scoliosis in 22% (11 of 50). Surgery in a specialized unit is satisfactory management for severe scoliosis in Rett syndrome. Recommendations include planning for surgery when the curve passes 40°, ensuring optimal nutrition before and after surgery, robust fixture of the whole spine in two stages, familiarization of the surgical team with the individual and the disorder before the operation, and inclusion of the main carer in the hospital care team. Parents form an important part of the management team. Families also require support during and after this stressful major procedure. (J Child Neurol 2003;18:703—708).

NTNG1 Mutations are a Rare Cause of Rett Syndrome

A translocation that disrupted the netrin G1 gene (NTNG1) was recently reported in a patient with the early seizure variant of Rett syndrome (RTT). The netrin G1 protein (NTNG1) has an important role in the developing central nervous system, particularly in axonal guidance, signalling and NMDA receptor function and was a good candidate gene for RTT. We recruited 115 patients with RTT (females: 25 classic and 84 atypical; 6 males) but no mutation in the MECP2 gene. For those 52 patients with epileptic seizure onset in the first 6 months of life, CDKL5 mutations were also excluded. We aimed to determine whether mutations in NTNG1 accounted for a significant subset of patients with RTT, particularly those with the early onset seizure variant and other atypical presentations. We sequenced the nine coding exons of NTNG1 and identified four sequence variants, none of which were likely to be pathogenic. Mutations in the NTNG1 gene appear to be a rare cause of RTT but NTNG1 function demands further investigation in relation to the central nervous system pathophysiology of the disorder.

Rett syndrome: critical examination of clinical features, serial EEG and video-monitoring in understanding and management

We studied data on seizures, vacant spells and breathing dysrhythmia from the British Rett Survey and 150 electroencephalographic records from 78 classic cases, including 23 with prolonged synchronous recordings of EEG, respiration and movement. The proportion of abnormal records increased from 6 of 18 (33%) during the first 6 months of the regression period to 44 of 59 (75%) in the later period to 6 years, the increase in abnormality following rather than preceding the onset of regression. In young girls the EEG abnormality increased in sleep but decreased during episodic hyperventilation and breath-holding. Epileptogenic activity was commonly present without clinical seizures. Eleven vacant spells were monitored and were not epileptic but related to the breathing abnormality. Full monitoring is essential when supposed seizures are intractable. The intermittent EEG abnormality and behavioural changes indicate abnormal fluctuating arousal possibly of midbrain or brainstem origin.