Respiration patterns during feeding in Rett syndrome

Breathing disturbances in Rett syndrome

Rett Syndrome is an X-linked neurological disorder characterized by behavioral and neurological regression, seizures, motor deficits, and dysautonomia. A particularly prominent presentation includes breathing abnormalities characterized by breathing irregularities, hyperventilation, repetitive breathholding during wakefulness, obstructive and central apneas during sleep, and abnormal responses to hypoxia and hypercapnia. The condition and pathology of the respiratory system is further complicated by dysfunctions of breathing-motor coordination, which is reflected in dysphagia. The discovery of the X-linked mutations in the MECP2 gene has transformed our understanding of the cellular and molecular mechanisms that are at the root of various clinical phenotypes. However, the genotype-phenotype relationship is complicated by various factors which include not only X-inactivation but also consequences of the intermittent hypoxia and oxidative stress associated with the breathing abnormalities.

The Pathophysiology of Rett Syndrome With a Focus on Breathing Dysfunctions

Rett syndrome (RTT), an X-chromosome-linked neurological disorder, is characterized by serious pathophysiology, including breathing and feeding dysfunctions, and alteration of cardiorespiratory coupling, a consequence of multiple interrelated disturbances in the genetic and homeostatic regulation of central and peripheral neuronal networks, redox state, and control of inflammation. Characteristic breath-holds, obstructive sleep apnea, and aerophagia result in intermittent hypoxia, which, combined with mitochondrial dysfunction, causes oxidative stress-an important driver of the clinical presentation of RTT.

Ponto-medullary nuclei involved in the generation of sequential pharyngeal swallowing and concomitant protective laryngeal adduction in situ

Both swallowing and respiration involve postinspiratory laryngeal adduction. Swallowing-related postinspiratory neurons are likely to be located in the nucleus of the solitary tract (NTS) and those involved in respiration are found in the Kölliker-Fuse nucleus (KF). The function of KF and NTS in the generation of swallowing and its coordination with respiration was investigated in perfused brainstem preparations of juvenile rats (n = 41). Orally injected water evoked sequential pharyngeal swallowing (s-PSW) seen as phasic, spindle-shaped bursting of vagal nerve activity (VNA) against tonic postinspiratory discharge. KF inhibition by microinjecting isoguvacine (GABAA receptor agonist) selectively attenuated tonic postinspiratory VNA (n = 10, P < 0.001) but had no effect on frequency or timing of s-PSW. KF disinhibition after bicuculline (GABAA receptor antagonist) microinjections caused an increase of the tonic VNA (n = 8, P < 0.01) resulting in obscured and delayed phasic s-PSW. Occurrence of spontaneous PSW significantly increased after KF inhibition (P < 0.0001) but not after KF disinhibition (P = 0.14). NTS isoguvacine microinjections attenuated the occurrence of all PSW (n = 5, P < 0.01). NTS bicuculline microinjections (n = 6) resulted in spontaneous activation of a disordered PSW pattern and long-lasting suppression of respiratory activity. Pharmacological manipulation of either KF or NTS also triggered profound changes in respiratory postinspiratory VNA. Our results indicate that the s-PSW comprises two functionally distinct components. While the primary s-PSW is generated within the NTS, a KF-mediated laryngeal adductor reflex safeguards the lower airways from aspiration. Synaptic interaction between KF and NTS is required for s-PSW coordination with respiration as well as for proper gating and timing of s-PSW.

Assessment and management of nutrition and growth in Rett syndrome

OBJECTIVES

We developed recommendations for the clinical management of poor growth and weight gain in Rett syndrome through evidence review and the consensus of an expert panel of clinicians.

METHODS

Initial draft recommendations were created based upon literature review and 34 open-ended questions in which the literature was lacking. Statements and questions were made available to an international, multidisciplinary panel of clinicians in an online format and a Microsoft Word-formatted version of the draft via e-mail. Input was sought using a 2-stage modified Delphi process to reach consensus. Items included clinical assessment of growth, anthropometry, feeding difficulties and management to increase energy intake, decrease feeding difficulties, and consideration of gastrostomy.

RESULTS

Agreement was achieved on 101 of 112 statements. A comprehensive approach to the management of poor growth in Rett syndrome is recommended that takes into account factors such as feeding difficulties and nutritional needs. A body mass index of approximately the 25th centile can be considered as a reasonable target in clinical practice. Gastrostomy is indicated for extremely poor growth, if there is risk of aspiration and if feeding times are prolonged.

CONCLUSIONS

These evidence- and consensus-based recommendations have the potential to improve care of nutrition and growth in a rare condition and stimulate research to improve the present limited evidence base.

Gastrointestinal and nutritional problems occur frequently throughout life in girls and women with Rett syndrome

OBJECTIVE

We conducted a nationwide survey to determine the prevalence of common gastrointestinal and nutritional disorders in Rett syndrome (RTT) based on parental reporting and related the occurrence of these problems to age and methyl-CpG-binding protein 2 (MECP2) gene status.

METHODS

We designed a questionnaire that probed symptoms, diagnoses, diagnostic tests, and treatment interventions related to gastrointestinal and nutritional problems in RTT. The International Rett Syndrome Foundation distributed the questionnaire to 1666 family-based members and forwarded their responses for our review. We interrogated the Rare Disease Clinical Research Network database to supplement findings related to medications used to treat gastrointestinal problems in RTT.

RESULTS

Parents of 983 female patients with RTT (59%) responded and identified symptoms and diagnoses associated with gastrointestinal dysmotility (92%), chewing and swallowing difficulties (81%), weight deficits or excess (47%), growth deficits (45%), low bone mineral content or fractures (37%), and biliary tract disorders (3%). Height-for-age, weight-for-age, and body mass index z scores decreased significantly with age; height- and weight-, but not body mass index-for-age z scores were significantly lower in female subjects with MECP2 mutations than in those without. Vomiting, nighttime awakening, gastroesophageal reflux, chewing difficulty, and choking with feeding were significantly less likely to occur with increasing age. Short stature, low bone mineral content, fractures, and gastrostomy placement were significantly more likely to occur with increasing age. Chewing difficulty, choking with feeding, and nighttime awakening were significantly less likely to occur, whereas short stature was significantly more likely to occur, in female subjects with MECP2 mutations than in those without. Diagnostic evaluations and therapeutic interventions were used less frequently than the occurrence of symptoms or diagnoses in the RTT cohort.

CONCLUSIONS

Gastrointestinal and nutritional problems perceived by parents are prevalent throughout life in girls and women with RTT and may pose a substantial medical burden for their caregivers. Physician awareness of these features of RTT may improve the health and quality of life of individuals affected with this disorder.

Communication and eating proficiency in 125 females with Rett syndrome: The Swedish Rett center survey

PURPOSE

To describe communication and eating proficiency and related factors in Swedish females with Rett syndrome, from a parental/caregiver view.

METHOD

Data from a questionnaire were used and approached descriptively, qualitatively and comparatively. Parents/caregivers of 125 females with Rett syndrome completed the survey. The mean age of the females was 19.6 years.

RESULTS

Communication: expressive language was limited and the most common way of expressing will was by producing motor acts, 50% of which were higher level of language (eye- and finger-pointing and gestures). Results also showed communicative behaviour was demonstrated during social activities. Eating proficiency: For eight specific types of eating difficulties, the majority of the females suffered from none, one or two of them. There were significant associations of some specific eating difficulties with breathing dysfunctions and food consistency, but not with dental or oral problems.

CONCLUSIONS

Results from this study have confirmed that verbal communication in Rett syndrome is limited. Despite a lack of verbal communication the females in this study were reported to need and enjoy social interplay. Outcomes concerning eating were generally good. For optimal intervention, it is recommended that family and professionals work together to evaluate eating situations and communication ability for females with Rett syndrome.

Guided eating or feeding: three girls with Rett syndrome

Rett syndrome (RTT) considerably limits participation in daily activities but food and mealtimes are most often motivating activities for persons with RTT. The aim of this study was to investigate whether there is a difference in participation during meals when the persons eating do so through guided eating compared with being fed.Three girls with classic RTT participated in a study inspired by single-subject design. Investigation was performed during two meals at which the girls were fed and during a seven- to eight-week period when guided eating took place. Video analysis and registration forms were used, investigating (1) coordination between opening of the mouth and spoon movement, (2) signs of involvement during the meal, and (3) cooperation in arm movements during guided eating. Guided eating led to improved coordination between opening of the mouth and spoon movement, resulting in opening of the mouth before the spoon arrived, for all of the girls. Signs of involvement changed in two of the girls. According to the guiders, they were able to feel cooperation in arm movements during the different food intake sequences in all three girls. These results indicate that guided eating improved involvement and participation in the eating process in these girls.

Breathing dysfunction in Rett syndrome: understanding epigenetic regulation of the respiratory network

Severely arrhythmic breathing is a hallmark of Rett syndrome (RTT) and profoundly affects quality of life for patients and their families. The last decade has seen the identification of the disease-causing gene, methyl-CpG-binding protein 2 (Mecp2) and the development of mouse models that phenocopy many aspects of the human syndrome, including breathing dysfunction. Recent studies have begun to characterize the breathing phenotype of Mecp2 mutant mice and to define underlying electrophysiological and neurochemical deficits. The picture that is emerging is one of defects in synaptic transmission throughout the brainstem respiratory network associated with abnormal expression in several neurochemical signaling systems, including brain-derived neurotrophic factor (BDNF), biogenic amines and gamma-amino-butyric acid (GABA). Based on such findings, potential therapeutic strategies aimed at improving breathing by targeting deficits in neurochemical signaling are being explored. This review details our current understanding of respiratory dysfunction and underlying mechanisms in RTT with a particular focus on insights gained from mouse models.

Neuromodulation and the orchestration of the respiratory rhythm

The respiratory system is continuously modulated by numerous aminergic and peptidergic substances that act at all levels of integration: from the sensory level to the level of central networks and motor nuclei. The same neuronal networks receive inputs from multiple modulators released locally as well as from distal nuclei. All parameters of respiratory control are controlled by multiple neuromodulators. By partly converging onto similar G-proteins and second messenger systems, acetylcholine, norepinephrine, histamine, serotonin (5-HT), dopamine, ATP, substance P, cholecystokinin (CCK) can increase frequency, regularity and amplitude of respiratory activity. Yet, the same modulator can also exert differential effects on respiratory activity by acting on different receptors partly in the same neurons. In the pre-Bötzinger complex (pre-BötC) modulators can differentially modulate frequency and amplitude in different types of pacemaker neurons. Similarly motoneurons located in different motor nuclei receive differential amplitude modulation from different modulators. Thus, modulators are capable of orchestrating and modulating different parameters of respiratory activity by differentially targeting different cellular targets. A disturbance in modulatory control may lead to Sudden Infant Death Syndrome (SIDS) and erratic breathing.

The use of pulse oximetry as a screening assessment for paediatric neurogenic dysphagia

PURPOSE

Early screening and intervention for dysphagia is crucial to offset potential outcomes such as compromised nutrition or reduced respiratory function. Current paediatric dysphagia screening tests are subjective with poor sensitivity and specificity. The present study examined whether an objective method, pulse oximetry (measuring oxygen saturation (SpO2) levels), could differentiate between children with and without dysphagia, in relation to (1) Average pre-feeding baseline SpO2 levels; (2) Average feeding SpO2 levels; (3) Average post-feeding SpO2 levels; and (4) The number of events of oxygen desaturation pre-, during and after feeding.

METHODS

Nine participants with chronic neurological disability (CND) (7 F, 2 M) (9; 7-15; 11 years) and nine control participants matched for age (9; 5-16; 0 years) and sex were assessed using a clinical bedside evaluation (CBE) and pulse oximetry.

RESULTS

A statistically significant difference was found in SpO2 levels between the two groups (p < 0.001) during oral feeding only (sensitivity, 88.9%; specificity, 88.9%). Only three children with dysphagia experienced 'events' of SpO2 desaturation during feeding.

CONCLUSION

Pulse oximetry may provide a useful adjunct to the CBE for dysphagia screening, with average SpO2 levels during feeding predicting those with and without dysphagia with moderate levels of sensitivity and specificity. The finding of individual variation in desaturation 'events', however, warrants the provision of further data on large homogenous populations to provide definitive criterion for pathological SpO2 levels associated with dysphagia during oral feeding.

Breathing dysfunctions associated with impaired control of postinspiratory activity in Mecp2-/y knockout mice

Rett syndrome (RTT) is an inborn neurodevelopmental disorder caused by mutations in the X-linked methyl-CpG binding protein 2 gene (MECP2). Besides mental retardation, most patients suffer from potentially life-threatening breathing arrhythmia. To study its pathophysiology, we performed comparative analyses of the breathing phenotype of Mecp2-/y knockout (KO) and C57BL/6J wild-type mice using the perfused working heart-brainstem preparation (WHBP). We simultaneously recorded phrenic and efferent vagal nerve activities to analyse the motor pattern of respiration, discriminating between inspiration, postinspiration and late expiration. Our results revealed respiratory disturbances in KO preparations that were similar to those reported from in vivo measurements in KO mice and also to those seen in RTT patients. The main finding was a highly variable postinspiratory activity in KO mice that correlated closely with breathing arrhythmias leading to repetitive apnoeas even under undisturbed control conditions. Analysis of the pontine and peripheral sensory regulation of postinspiratory activity in KO preparations revealed: (i) prolonged apnoeas associated with enhanced postinspiratory activity after glutamate-induced activation of the pontine Kölliker-Fuse nucleus; and (ii) prolonged apnoeas and lack of reflex desensitization in response to repetitive vagal stimulations. We conclude that impaired network and sensory mediated synaptic control of postinspiration induces severe breathing dysfunctions in Mecp2-/y KO preparations. As postinspiration is particularly important for the control of laryngeal adductors, the finding might explain the upper airway-related clinical problems of patients with RTT such as apnoeas, loss of speech and weak coordination of breathing and swallowing.

Mecp2 deficiency disrupts norepinephrine and respiratory systems in mice

Rett syndrome is a severe X-linked neurological disorder in which most patients have mutations in the methyl-CpG binding protein 2 (MECP2) gene and suffer from bioaminergic deficiencies and life-threatening breathing disturbances. We used in vivo plethysmography, in vitro electrophysiology, neuropharmacology, immunohistochemistry, and biochemistry to characterize the consequences of the MECP2 mutation on breathing in wild-type (wt) and Mecp2-deficient (Mecp2-/y) mice. At birth, Mecp2-/y mice showed normal breathing and a normal number of medullary neurons that express tyrosine hydroxylase (TH neurons). At approximately 1 month of age, most Mecp2-/y mice showed respiratory cycles of variable duration; meanwhile, their medulla contained a significantly reduced number of TH neurons and norepinephrine (NE) content, even in Mecp2-/y mice that showed a normal breathing pattern. Between 1 and 2 months of age, all unanesthetized Mecp2-/y mice showed breathing disturbances that worsened until fatal respiratory arrest at approximately 2 months of age. During their last week of life, Mecp2-/y mice had a slow and erratic breathing pattern with a highly variable cycle period and frequent apneas. In addition, their medulla had a drastically reduced number of TH neurons, NE content, and serotonin (5-HT) content. In vitro experiments using transverse brainstem slices of mice between 2 and 3 weeks of age revealed that the rhythm produced by the isolated respiratory network was irregular in Mecp2-/y mice but could be stabilized with exogenous NE. We hypothesize that breathing disturbances in Mecp2-/y mice, and probably Rett patients, originate in part from a deficiency in noradrenergic and serotonergic modulation of the medullary respiratory network.