Rett syndrome. An update and review for the primary pediatrician

Congenital Hypothyroidism and Brain Development: Association With Other Psychiatric Disorders

Thyroid hormones play an important role in brain development, and thyroid hormone insufficiency during the perinatal period results in severe developmental delays. Perinatal thyroid hormone deficiency is clinically known as congenital hypothyroidism, which is caused by dysgenesis of the thyroid gland or low iodine intake. If the disorder is not diagnosed or not treated early, the neuronal architecture is perturbed by thyroid hormone insufficiency, and neuropathological findings, such as abnormal synapse formation, defects in neuronal migration, and impairment of myelination, are observed in the brains of such patients. Furthermore, the expression of psychiatric disorder-related molecules, especially parvalbumin, is significantly decreased by thyroid hormone insufficiency during the perinatal period. Animal experiments using hypothyroidism models display decreased parvalbumin expression and abnormal brain architecture, and these experimental results show reproducibility and stability. These basic studies reinforce the results of epidemiological studies, suggesting the relevance of thyroid dysfunction in psychiatric disorders. In this review, we discuss the disruption of brain function associated with congenital hypothyroidism from the perspective of basic and clinical research.

Eating practices, nutritional status and constipation in patients with Rett syndrome

BACKGROUND: Disturbance in chewing, swallowing and digestive motility may predispose to feeding and nutritional abnormalities in patients with Rett syndrome. OBJECTIVE: To evaluate the dietary habits, nutritional status and the prevalence of constipation in patients with classical Rett syndrome. METHODS: Twenty seven female patients between the ages of 2.6 and 21.8 years were studied. The following parameters were evaluated: food register, weight, height and intestinal movement characteristics. Weight and height were compared with the National Center for Health Statistics standards. RESULTS: The inability to ingest solid foods was observed in 80.8% of the patients. A height-to-age deficit was observed in 13 (48.1%) of the girls, being more intense in patients at stage IV. Weight-for-height deficit was found in 10 (37.0%) patients, 15 (55.6%) showed normal weight and 2 (7.4%) were overweight for their height. The median ingestion of energy, according to weight-for-height, was equal to 106.6%. Insufficient iron ingestion was observed in 63.0% and insufficient calcium in 55.6% of the patients. Constipation was verified in 74.1% of the patients and did not show a relationship with the quantity of fiber in the diet. CONCLUSION: Various nutritional problems, as well as, intestinal constipation were observed in these patients with Rett syndrome, and they must be considered in the multidisciplinary therapeutic planning of these individuals.

Effects of acetyl-L-carnitine on cardiac dysautonomia in Rett syndrome: prevention of sudden death?

There is a higher incidence of sudden death in patients with Rett syndrome than individuals in the general population. Previous studies have implicated cardiac dysautonomia and a long QT interval as causative factors. Because carnitine plays a critical role in cellular metabolism and may have beneficial effects on cardiac and nerve function, we investigated the effects of long-term treatment with acetyl-L-carnitine on heart rate variability and electrocardiographic abnormalities in 10 girls with Rett syndrome and compared the results with 12 control patients (girls with Rett syndrome who were not treated). The age range of the subjects was 2-21 years. The study design called for the evaluation of heart rate variability, corrected QT interval, and QTc dispersion. In the 10 Rett girls treated with acetyl-L-carnitine, a significant increase in heart rate variability was observed. To explain these results, we hypothesize that acetyl-L-carnitine has a neurotrophic action on the cardiac autonomic nervous system. This effect may reduce the risk of sudden death in patients with this syndrome.

Severe sinus bradycardia in a patient with Rett syndrome: a new cause for a pause?

Rett syndrome is a progressive disorder seen primarily in young females. It is characterized by autonomic dysfunction affecting many organ systems. Although sudden death is common in these patients, little is known about the cardiovascular manifestations of this dysautonomia. Earlier reports focused on the role of sympathetic overactivity manifest as reduced heart rate variability and prolonged QT intervals indicating a propensity for lethal ventricular arrhythmias. Bradyarrhthmias and sinus node dysfunction, however, have not previously been reported. We describe a 2-year-old with Rett syndrome and severe sinus bradycardia requiring a pacemaker implant. This case represents the first description of a new cardiovascular manifestation of Rett syndrome and may provide an explanation for sudden and unexpected death in some of these patients.

Progressive cardiac dysautonomia observed in patients affected by classic Rett syndrome and not in the preserved speech variant

Incidence of sudden death in Rett syndrome is greater than that of the general population, and cardiac electrical instability is a prime suspect cause. The objective of the present study was the evaluation of heart rate variability, a marker of autonomic activity, in females affected by classic Rett syndrome and atypical variants for a possible explanation of the higher risk for sudden death observed in these subjects. Our study showed that girls with classic Rett syndrome had significantly lower heart rate variability and longer corrected QT intervals than in atypical Rett syndrome and age-matched healthy girls. Reduction of heart rate variability progresses with age and with the clinical stage of the syndrome. These results suggest the possible role of the progressive cardiac dysfunction in the sudden death associated with Rett syndrome.

Organ growth in Rett syndrome: a postmortem examination analysis

Rett syndrome is a disorder of unknown etiology in females that manifests as severe mental and motor retardation during the first years of life. A postnatal pattern of altered growth is its earliest clinical expression. Head growth decelerates during the first year of age and is followed by a decline in somatic (height/weight) growth. The decreased occipitofrontal circumference (OFC) is reflected in decreased brain size, and measurements of the dendrites of cortical neurons suggest that a developmental and growth arrest have occurred. To further document growth in Rett syndrome, measurements of organ weights, as recorded in 39 postmortem examination studies were compared with normal organ weights for females of comparable age and height. These organ weights suggest that the pattern of growth failure in Rett syndrome, as compared with other forms of mental handicap, such as Down syndrome and Turner's syndrome, may be unique. In Rett syndrome the rate of brain growth, as derived from OFC, decelerates after birth. The increment in normal brain weight after 4 years of age, the age of the first postmortem examinations, is not observed in the Rett brain. The heart, kidneys, liver, and spleen grow at the normally defined rate until 8-12 years of age, when their growth rate decelerates, but their growth continues achieving organ weights that are appropriate for the height of the female. Adrenal weights are normal. These observations suggest that despite a generalized decreased growth in Rett syndrome the brain may be preferentially affected in this syndrome.

Diagnosis of Rett syndrome: can a radiograph help?

Rett syndrome (RS), a neurodevelopmental disorder almost exclusively affecting girls, is associated with severe intellectual and motor disability. In the absence of biological markers, diagnosis is determined by a set of clinical criteria. In a previous study in Scotland, shortening of the fourth metatarsal was reported clinically in 20% of classical RS cases aged 5 years or older. The Australian Rett Syndrome Study database has facilitated a population-based radiological study of the hands and feet of girls with RS. Straight radiographs of hands and feet were available from 94 cases, representing 70.1% of the known RS population in Australia. Control radiographs were matched for age, sex, and laterality. Relative shortening of the fourth metacarpal/metatarsal was assessed using the sign method. A short ulna (negative ulna variance) was defined as the distal articular surface of the ulna being at least 5mm proximal to the distal articular surface of the radius. A positive metacarpal sign was twice as common in verified cases of RS than in controls in the right but not the left hand. A short ulna was more common in subjects with RS than in controls. A short fourth metatarsal was also more common among subjects with RS. More than half (56.6%) the girls with RS over the age of 4 years had a negative ulnar variance in either wrist or a metatarsal sign in either foot. These findings will assist with the diagnosis of RS and may help direct research towards the location of the molecular defect.

Annotation: behavioural phenotypes: a window onto the biology of behaviour

Characteristic behavioural patterns (including cognitive processes and social interactions) have been reported in a number of syndromes arising from genetic or chromosomal abnormalities, suggesting that molecular analysis of the underlying defect could reveal the biological basis of the behavioural phenotype. Because of the rarity of many of the syndromes, and the complexity of their genetic basis, there are great difficulties in establishing the validity of the association between syndrome and behavioural phenotype. Nevertheless, evidence from animal studies with relevance to human behavioural phenotypes shows that the pathway from genotype to phenotype may be accessible by careful delineation of behavioural phenotypes.