Biomedical subjects
Publications and source records attributed to A K Percy.
Girls with Rett syndrome had significantly longer corrected QT intervals (p < 0.001) and more T-wave abnormalities (p < 0.001) than were found in age-matched healthy girls. With advancing stages of the syndrome, the proportion of corrected QT interval prolongations and T-wave changes increased. The findings suggest a possible cardiac basis for sudden, unexpected death in Rett syndrome.
We have found mutations in the Menkes disease gene (MNK) which impair, but do not abolish, correct mRNA splicing in patients with less severe clinical phenotypes. In one family, four males aged 2-36 years with a distinctive Menkes variant have a mutation at the +3 position of a splice donor site near the 3' end of the Menkes coding sequence that is associated with exon skipping and a stable mutant transcript. In an unrelated 15-year-old male with typical occipital horn syndrome, a point mutation at the -2 exonic position of a splice donor site in the middle of the gene causes exon-skipping and activation of a cryptic splice acceptor site. In both mutations, maintenance of some normal splicing is demonstrable by RT-PCR, cDNA sequencing and ribonuclease protection.
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.
To determine whether alterations in energy balance account for growth failure in Rett syndrome, we measured dietary energy intakes, fecal fat losses, activity patterns, and sleeping as well as quietly and actively awake metabolic rates in Rett syndrome girls and healthy controls. Dietary energy intakes and fecal fat losses did not differ between the groups. Metabolic rates while sleeping and quietly awake were 23% lower (P < .05) in Rett syndrome girls than in controls; metabolic rates while actively awake did not differ between the groups. However, because of the 2.4-fold greater time (P < .001) spent in involuntary motor movement, energy expenditure associated with activity was twofold greater (P < .05) in Rett syndrome girls than in controls. Although total daily energy expenditure of the two groups did not differ significantly, energy balance was less positive in the Rett syndrome girls than in the controls. This small difference in energy balance, if sustained over months to years, is sufficient to account for growth failure in Rett syndrome girls.
OBJECTIVE: To define the growth pattern of girls with Rett syndrome with respect to height, weight, and fronto-occipital head circumference. DESIGN: Longitudinal with irregular intervals between measurements. SETTING: Rett Syndrome Program Project at Baylor College of Medicine, Houston, Tex. PARTICIPANTS: Ninety-six girls fulfilling criteria for Rett syndrome; comparison group with standard growth curves. SELECTION PROCEDURE: Consecutive entries into the Rett Syndrome Program Project. INTERVENTION: None. MEASUREMENTS/MAIN RESULTS: Height, weight, and fronto-occipital head circumference data were grouped into intervals. Group medians were then generated. Regression lines were fitted through the median points and plotted on standard growth charts. Deceleration of growth velocities began at age 3 months and persisted through age 18 years. CONCLUSIONS: Early deceleration of head growth, followed by deceleration of weight and height measurements, appears to be a growth pattern characteristic of Rett syndrome. This pattern of growth may provide the earliest clinical indicator for the diagnosis of Rett syndrome.
The Texas Rett Syndrome Registry maintains the largest population-based registry of cases and potential cases of Rett syndrome in the world. The most precise estimate of the prevalence of Rett syndrome of 1 per 22800 (0.44/10000) females aged 2 through 18 years of age was generated from this Registry. In addition, the first prevalence figures for black and Hispanic female cases were estimated. Registry cases are actively ascertained from multiple sources. Registry staff identify presumptive cases from review of information provided to the Registry by the parent or guardian. Preliminary diagnostic evaluation includes standardized review of medical records and videotape of key behaviors. Diagnosis is confirmed at clinical evaluation. The active surveillance system is monitored with the two-source capture-recapture methodology and case ascertainment is projected. The 1990 prevalence estimate of Rett syndrome indicates that the syndrome occurs less frequently than previously estimated. Until a biologic marker for Rett syndrome is identified or a standard definition for an incident case of Rett syndrome is designated, the prevalence of Rett syndrome will remain a major investigative issue of its epidemiology, and the Registry will be an important, systematic mean to gather case material for clinical and laboratory studies providing the foundation for the development of preventive interventions.
Congenital cytomegalovirus (CMV) infection is a major public health problem because 30,000 to 40,000 neonates with the infection are born each year in the United States. Although 90% of the congenitally infected infants are asymptomatic at birth, evidence is accumulating that these infants are at risk for audiologic, neurologic, and developmental sequelae. The current study describes the audiologic outcome of 59 infants with asymptomatic congenital CMV infection compared with 26 control infants. Eight of 59 infected infants had congenital sensorineural hearing loss (SNHL) but none of the control subjects did. Longitudinal audiologic assessments revealed that 5 of the 8 infants had further deterioration of their SNHL; a ninth infant with initially normal hearing experienced a unilateral SNHL during the first year of life, with further deterioration subsequently. The frequency of SNHL was similar for infected infants born to mothers with recurrent CMV infections during pregnancy (2 of 9) and for those born to mothers who experienced primary CMV infections (5 of 26). There was a significant difference between the occurrence of hearing loss in infected infants with normal computed tomographic scans (2 of 40) compared with those with either periventricular radiolucencies (4 of 13) or calcifications (1 of 3). Children with SNHL often have no identified cause of the loss; thus, it is likely that many of these children had asymptomatic congenital CMV infection. Given the progressive nature of SNHL associated with asymptomatic congenital CMV infection, longitudinal audiologic assessments are mandatory.
The present status of efforts in the USA to understand the genetic basis of the Rett syndrome (RS) is reviewed. Analysis of monozygotic and dizygotic twin data provide compelling support for a genetic mechanism. Similarly, support can be derived from familial cases following maternal lines. Special attention is directed to the X chromosome. Nonrandom X inactivation in the mother of half sisters and the identification of RS girls with translocations involving the X chromosome and separate autosomes have sharpened the focus molecular studies.
Based on data presented at the Tokyo Rett Syndrome Symposium, November 1990, actual neurobiological knowledge and interpretations are compiled. The underlying biological concepts, as well as the potential origin of the condition are particularly discussed.
The current status of neurochemistry research with respect to the Rett syndrome (RS) is reviewed and correlations developed with the previously described neuropathologic changes. Despite reports of abnormalities in intermediary metabolism and the biogenic amine neurotransmitters, follow-up studies have failed to support any consistent abnormality in either area. In general, the levels of membrane lipid constituents in various brain regions have been similar to control values. New information suggests a disturbance in the ganglioside pattern leading to a reduction in GD1a and GT1b gangliosides in cerebrum and cerebellum. The corresponding reduction of these gangliosides in cerebrospinal fluid, if shown to be specific for RS, could represent an important clue in confirming the clinical diagnosis. Evidence of pervasive growth failure is presented and the current status of the role of beta-endorphins in RS is described. Considerations regarding future directions for research in RS are presented. These strategies include an approach to the fundamental question, namely, the identification of the primary molecular defect.
Rett syndrome is a neurologic disorder characterized by early normal development followed by regression, acquired deceleration of head growth, autism, ataxia, and stereotypic hand movements. The exclusive occurrence of the syndrome in females and the occurrence of a few familial cases with inheritance through maternal lines suggest that this disorder is most likely secondary to a mutation on the X chromosome. To address this hypothesis and to identify candidate regions for the Rett syndrome gene locus, genotypic analysis was performed in two families with maternally related affected half-sisters by using 63 DNA markers from the X chromosome. Maternal and paternal X chromosomes from the affected sisters were separated in somatic cell hybrids and were examined for concordance/discordance of maternal alleles at the tested loci. Thirty-six markers were informative in at least one of the two families, and 25 markers were informative in both families. Twenty loci were excluded as candidates for the Rett syndrome gene, on the basis of discordance for maternal alleles in the half-sisters. Nineteen of the loci studied were chosen for multipoint linkage analysis because they have been previously genetically mapped using a large number of meioses from reference families. Using the exclusion criterion of a lod score less than -2, we were able to exclude the region between the Duchenne muscular dystrophy locus and the DXS456 locus. This region extends from Xp21.2 to Xq21-q23. The use of the multipoint linkage analysis approach outlined in this study should allow the exclusion of additional regions of the X chromosome as new markers are analyzed. This in turn will result in a defined region of the X chromosome that should be searched for candidate sequences for the Rett syndrome gene in both familial and sporadic cases.
Medulloblastoma biopsies are heterogenous and might contain normal brain tissue, which limits the usefulness of such tumor material for biochemical analyses. We have, therefore, examined the gangliosides and their metabolism using the medulloblastoma cell lines. Daoy and D341 Med, cultured both in vitro and as xenografts in nude mice. The ganglioside patterns in the Daoy showed a switch from a high GM2, 70% (mol% of total ganglioside sialic acid) and low lactoseries gangliosides (2%) content in monolayer cultures, to a high proportion of lactoseries gangliosides (50%) and virtually no GM2 (1%) in xenografts, but an increased proportion of other a-series gangliosides. The D341 Med showed a similar change regarding the lacto-series gangliosides from 1% in suspension culture to 10% in xenografts. The activity of five glycosyltransferases, GM3, GD3, GM2, GM1 and LA2 synthases, did not parallel the ganglioside patterns and could not account for the noted variations therein. In the Daoy cell line the LA2 synthase as well as the GM2 synthase activity was relatively high in both culture systems, despite the marked difference in the expression of GM2 and the lactoseries gangliosides. These results suggest that environmental factors play a crucial role for the in vivo activity of the glycosyltransferases.
Phosphatidylcholine (PC) metabolism in bovine adrenal chromaffin cells has been studied in vivo with 100 MHz 13C NMR spectroscopy. The incorporation of 13[CH3]choline was examined in cells embedded in 1% agarose strands and perfused at 37 degrees C. The pattern of 13C NMR spectroscopy. The incorporation of [13CH3]choline incorporation into PC of suspension cultures of chromaffin cells. The chemical shifts of labelled carbons in [13CH3]choline before and after their incorporation into PC are identical (ca 56.4 ppm). Incorporated [13CH3]choline can be released from the cells by phospholipase D which reduces the cellular PC signal by greater than 85%, indicating that a major fraction of the labelled PC is on the external membrane surface. This application of NMR spectroscopy provides a basis for direct measurement of the in vivo metabolism of PC in functioning adrenal chromaffin cells.
Clinical, neurochemical and neuropathological findings on a case of late-infantile Gaucher disease with oculomotor apraxia, progressive myoclonus and prominent bulbar signs are reported. There was a marked increase in glucosylceramide in cerebral cortex and cerebellum; the increase was more in the range of that seen in the Norrbottnian type III than in type II Gaucher disease. Cerebral cortical changes were characterized by a band-like intraparenchymal accumulation of Gaucher cells in lamina IV with an accompanying astrogliosis. In the cerebellum, a focal severe loss of granule cells and a global loss of dentate nucleus neurons was recorded. Milder changes were seen in thalamus and brain stem where perivascular accumulation of Gaucher cells was present in all regions. The cerebral cortical changes resembled those seen in type II Gaucher disease and was much more marked than in the Norrbottnian type III, whereas the changes in the dentate nucleus were more severe than in both type II and type III. The phenotypic variability with different patterns of clinical symptoms and neuropathological changes in neuronopathic Gaucher disease is discussed.
Cultured adrenal chromaffin cells, representing a virtually homogeneous population of neuronal elements, have been utilized to examine the final enzymes in the formation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), namely, choline phosphotransferase, ethanolaminephosphotransferase, and the N-methyltransferases in the sequential methylation of PE to PC. Each enzyme has been characterized extensively in terms of substrate requirements, pH optima, detergent and cation effects, and response to inhibitors revealing properties very similar to those in other neural preparations. The respective activities are stable for up to two weeks of adrenal chromaffin cell culture suggesting that this system is a suitable model for examining the relative roles and the regulation of each pathway in PC formation.
The developmental pattern of gangliosides in human fetal brain should reflect the activities of the respective glycosyltransferases. LA2-synthase activity, along with that of GM3-, GD3-, GM2-, and GM1-synthases, was determined in human fetal brain at 10-22 weeks of gestation. LA2-synthase is the pivotal enzyme in lacto series ganglioside formation. LA2-synthase activity decreased during the study period, mirroring a similar temporal decline in levels of the lacto series gangliosides, particularly 3'-isoLM1. The developmental profiles of the ganglio series glycosyltransferase activities demonstrate distinct changes that correspond to the ganglioside pattern between fetal weeks 10 and 22. In particular, the marked increase in GM2-synthase activity at 20 and 22 weeks of gestation and the decline in GD3-synthase activity after 15 weeks could explain the prominent expression of the a series gangliosides in this period of rapid neuronal outgrowth. However, a similar decline (two- to 2.5-fold) in GM3-synthase activity suggests a more likely conclusion, namely, that the two sialyltransferase activities are derived mainly from astroglial cells, which show a marked proliferation during the 10-15th fetal weeks. The data do not negate the hypothesis that GM3- and GD3-synthase are the critical enzymes in the regulation of ganglioside biosynthesis but do indicate a need to reevaluate the significance of GM2-synthase in expression of the a series gangliosides.
Twenty-eight infants with asymptomatic congenital cytomegalovirus infection and 13 control infants were followed up prospectively. Congenital sensorineural hearing loss was documented by auditory brain-stem responses in four infected infants (two had mild bilateral loss, one had mild unilateral loss, and one had extreme unilateral loss) but in no controls. Four infected infants had diffuse periventricular radiolucencies on computed tomographic scan; none had calcifications or ventriculomegaly. No differences between groups were noted on neurologic examination results or on the Bayley Mental Developmental Index; however, one infected infant had a severely delayed Bayley Psychomotor Developmental Index score. In addition, the mean Mental Developmental Index score of the four infected infants with diffuse periventricular radiolucencies was significantly below that of the remaining infected infants (93 +/- 8 vs 109 +/- 13). These data suggest that asymptomatic congenital cytomegalovirus infection may be associated with a broad range of audiologic, subtle neuroradiologic, and neurodevelopmental differences in early infancy.
Rett syndrome is a neurodegenerative disorder that occurs exclusively in females. The syndrome is sporadic in most cases with the exception of a few familial cases with an inheritance pattern through maternal lines. These observations raised the possibility that Rett syndrome may be due to an X-linked dominant mutation which is lethal in the male. To evaluate this hypothesis, we have systematically performed high-resolution chromosome analysis on 28 patients with Rett syndrome searching for deletions and/or translocations. In one patient, a de novo balanced translocation was observed with the chromosome constitution of 46,X,t(X;3) (p22.11;q13.31). This finding supports the hypothesis of an X-linked dominant mutation and suggests that the Rett gene might map to distal Xp21 or proximal Xp22.