Research on Rett syndrome: strategy and preliminary results

Rett syndrome

Rett syndrome (RS) is a neurological disorder that mainly, and possibly exclusively, affects girls. After its description in 1966 by Andreas Rett in the Wiener Klinische Wochenschrift, awareness and interest in RS were enhanced by the 1983 report of Hagberg et al. in the Annals of Neurology. Diagnosis, and indeed the hypothesis that it exists, continue to be based upon a consistent constellation of clinical features observed in thousands of female patients world-wide. A diagnostic marker has not been identified. Notwithstanding this serious limitation, it is generally agreed that RS is a distinct entity and that it is genetically determined. Although it is associated with devastating loss of function between infancy and the fifth year of life, its course becomes relatively static thereafter, setting it apart from most of the genetic neurodegenerative disorders of childhood. Neuropathological and neurochemical studies call attention to RS as a neurodevelopmental disorder. Clarification of its pathogenesis may provide new insight into normal brain development. This report summarizes existing information and concepts about RS, and presents recent advances.

Neuropathology of Rett syndrome: case report with neuronal and mitochondrial abnormalities in the brain

Neuronal changes in the brain of a Rett syndrome patient were examined in a frontal lobe biopsy performed at age 3 years and in the postmortem brain at age 15 years. In the brain biopsy, frontal cortex contained numerous scattered pyramidal neurons with cytoplasmic vacuolation and increased cytoplasmic density, with no neuronophagia or inflammation detected; electron microscopy showed these neurons to have large, lucent-appearing mitochondria, very abundant ribosomal content, and some lipofuscin granules. Postmortem brain 12 years later showed scattered neurons in frontal cortex, substantia nigra, and cerebellar folia, with increased electron density of the cytoplasm, stacks of ribosomal endoplasmic reticulum, and large amounts of disorganized membranous material, including autophagic-type organelles. Mitochondria of these neurons contained electron-dense, finely granular matrix inclusions; in the substantia nigra, some spherical mitochondrial inclusions completely filled the matrix space. Golgi preparations of (autopsy) frontal cortex and cerebellar folia showed truncation and thickening of dendrites and a degenerate appearance of cortical pyramidal neurons, similar to changes found in aged brain. Synaptophysin immunohistochemistry indicated that the density of synapses was not greatly altered compared to controls in frontal cortex and cerebellum. The patient also had a second genetic defect, severe combined immunodeficiency with thymic aplasia, which may be X-linked.

Abnormal carbohydrate metabolism in cerebrospinal fluid in Rett syndrome

We analyzed lactate, pyruvate, and citric acid cycle intermediates in cerebrospinal fluid by high-performance liquid chromatography in Rett syndrome patients (n = 27; mean age, 5.7 +/- 3.4 years) and age-matched female controls (n = 12; mean age, 7.0 +/- 3.3 years). The lactate, pyruvate, alpha-ketoglutarate, and malate were significantly elevated in Rett syndrome compared to the controls. The lactate/pyruvate ratio was not different. On the other hand, cerebrospinal fluid citrate, cis-aconitate, succinate, fumarate, and oxaloacetate were not significantly different in Rett syndrome patients than in the controls. We also evaluated the correlation between these acids and clinical symptoms and signs, including clinical stage, seizures medications (anticonvulsants or naltrexone), developmental quotient, self-abuse, and hyperventilation or apnea or both. The concentrations of all these acids did not differ significantly with clinical stage. Lactate elevation significantly correlated with apnea. Lactate and pyruvate elevation significantly correlated with hyperventilation or with both breathing abnormalities. Our observations in this sample of patients with Rett syndrome led us to speculate that patients with the Rett syndrome may have defective carbohydrate metabolism. Elevated mitochondrial reduced nicotinamide-adenine dinucleotide-linked substrates suggest that reduced nicotinamide-adenine dinucleotide-ubiquinone oxidoreductase may be deficient in the brain in Rett syndrome patients.