A phase Ib/IIa, open-label, multiple ascending-dose trial of domagrozumab in fukutin-related protein limb-girdle muscular dystrophy.

INTRODUCTION/AIMS: In this study we report the results of a phase Ib/IIa, open-label, multiple ascending-dose trial of domagrozumab, a myostatin inhibitor, in patients with fukutin-related protein (FKRP)-associated limb-girdle muscular dystrophy. METHODS: Nineteen patients were enrolled and assigned to one of three dosing arms (5, 20, or 40 mg/kg every 4 weeks). After 32 weeks of treatment, participants receiving the lowest dose were switched to the highest dose (40 mg/kg) for an additional 32 weeks. An extension study was also conducted. The primary endpoints were safety and tolerability. Secondary endpoints included muscle strength, timed function testing, pulmonary function, lean body mass, pharmacokinetics, and pharmacodynamics. As an exploratory outcome, muscle fat fractions were derived from whole-body magnetic resonance images. RESULTS: Serum concentrations of domagrozumab increased in a dose-dependent manner and modest levels of myostatin inhibition were observed in both serum and muscle tissue. The most frequently occurring adverse events were injuries secondary to falls. There were no significant between-group differences in the strength, functional, or imaging outcomes studied. DISCUSSION: We conclude that, although domagrozumab was safe in patients in limb-girdle muscular dystrophy type 2I/R9, there was no clear evidence supporting its efficacy in improving muscle strength or function.

Longitudinal functional and imaging outcome measures in FKRP limb-girdle muscular dystrophy.

BACKGROUND: Pathogenic variants in the FKRP gene cause impaired glycosylation of α-dystroglycan in muscle, producing a limb-girdle muscular dystrophy with cardiomyopathy. Despite advances in understanding the pathophysiology of FKRP-associated myopathies, clinical research in the limb-girdle muscular dystrophies has been limited by the lack of normative biomarker data to gauge disease progression. METHODS: Participants in a phase 2 clinical trial were evaluated over a 4-month, untreated lead-in period to evaluate repeatability and to obtain normative data for timed function tests, strength tests, pulmonary function, and body composition using DEXA and whole-body MRI. Novel deep learning algorithms were used to analyze MRI scans and quantify muscle, fat, and intramuscular fat infiltration in the thighs. T-tests and signed rank tests were used to assess changes in these outcome measures. RESULTS: Nineteen participants were observed during the lead-in period for this trial. No significant changes were noted in the strength, pulmonary function, or body composition outcome measures over the 4-month observation period. One timed function measure, the 4-stair climb, showed a statistically significant difference over the observation period. Quantitative estimates of muscle, fat, and intramuscular fat infiltration from whole-body MRI corresponded significantly with DEXA estimates of body composition, strength, and timed function measures. CONCLUSIONS: We describe normative data and repeatability performance for multiple physical function measures in an adult FKRP muscular dystrophy population. Our analysis indicates that deep learning algorithms can be used to quantify healthy and dystrophic muscle seen on whole-body imaging. TRIAL REGISTRATION: This study was retrospectively registered in clinicaltrials.gov (NCT02841267) on July 22, 2016 and data supporting this study has been submitted to this registry.

The NIH Toolbox for cognitive surveillance in Duchenne muscular dystrophy.

OBJECTIVE: We performed a prospective, cross-sectional cognitive assessment in subjects with Duchenne Muscular Dystrophy (DMD) and their biological mothers. METHODS: Thirty subjects with out-of-frame mutations in the dystrophin (DMD) gene, and 25 biological mothers were evaluated using the National Institutes of Health Toolbox Cognition Battery (NIHTB-CB). A parent completed the Behavior Rating Inventory of Executive Functioning (BRIEF), a standardized rating scale of executive functioning, for their child. Mothers completed self-reports of BRIEF and Neuro Quality-of-Life (NeuroQoL) Cognitive Function. RESULTS: Overall, the subjects with DMD scored approximately one standard deviation (SD) below age-corrected norms on the NIHTB-CB Total Cognition score. They scored 1.5 SD below age-corrected norms in Fluid Cognition, which evaluates the cognitive domains of executive function, working memory, episodic memory, attention, and processing speed. Their performance was consistent with age expectations (i.e., within 1 SD below age-corrected norms) in Crystalized Cognition, which evaluates vocabulary and reading. Subjects with DMD had higher T-scores in several domains of BRIEF, demonstrating greater difficulty in executive functioning. The biological mothers had overall average or above average T-scores on NIHTB-CB. Mothers who were carriers of DMD mutation performed lower overall compared to mothers who were not carriers of DMD mutation (Cohen's d = -1.1). Carrier mothers performed lower than average (1.5 SD) in Executive Function, measured by Flanker Inhibitory Control and Attention. Biological mothers scored within expected score ranges for adults in BRIEF and NeuroQoL. INTERPRETATION: The NIHTB-CB, combined with standardized self-reported measures, can be a sensitive screening tool for cognitive surveillance in DMD.

Are dopamine receptor and transporter changes in Rett syndrome reflected in Mecp2-deficient mice?

We tested the claim that the dopaminergic dysfunction of Rett Syndrome (RTT) also occurs in Mecp2-deficient mice that serve as a model of the syndrome. We used positron emission tomography (PET) to image dopamine D2 receptors (D2R) and transporters (DAT) in women with RTT and in Mecp2-deficient mice, and D1R and D2R density was measured in postmortem human tissue by autoradiography. Results showed 1) significantly reduced D2R density in the striatum of women with RTT compared to control subjects. 2) PET imaging of mouse striatum similarly demonstrated significant reductions in D2R density of 7-10 week-old hemizygous (Mecp2-null) and heterozygous (HET) mice compared to wild type (WT) mice. With age, the density of D2R declined in WT mice but not HET mice. 3) In contrast, postmortem autoradiography revealed no group differences in the density of D1R and D2R in the caudate and putamen of RTT versus normal control subjects. 4) In humans and in the mouse model, PET revealed only marginal group differences in DAT. The results confirm that dopaminergic dysfunction in RTT is also present in Mecp2-deficient mice and that reductions in D2R more likely explain the impaired ambulation and progressive rigidity observed rather than alterations in DAT.

Randomized open-label trial of dextromethorphan in Rett syndrome.

OBJECTIVE: To determine safety and perform a preliminary assessment of dose-dependent efficacy of dextromethorphan in normalizing electrographic spikes, clinical seizures, and behavioral and cognitive functions in girls with Rett syndrome. METHODS: We used a prospective randomized, open-label trial in fast metabolizers of dextromethorphan to examine the effect of dextromethorphan on core clinical features of Rett syndrome. Interictal spike activity and clinical seizures were determined using EEG and parent reporting. Cognitive data were obtained using the Mullen Scales of Early Learning and Vineland Adaptive Behavior Scales, while behavioral data were obtained from parent-completed checklists, the Aberrant Behavior Checklist-Community Version, and the Screen for Social Interaction. Anthropometric data were obtained according to the National Health and Nutrition Examination Survey. The Rett Syndrome Severity Scale provided a clinical global impression of the effect of dextromethorphan on clinical severity. RESULTS: Dextromethorphan is safe for use in 3- to 15-year-old girls with Rett syndrome. Thirty-five girls were treated with 1 of 3 doses of dextromethorphan over a period of 6 months. Statistically significant dose-dependent improvements were seen in clinical seizures, receptive language, and behavioral hyperactivity. There was no significant improvement in global clinical severity as measured by the Rett Syndrome Severity Scale. CONCLUSIONS: Dextromethorphan is a potent noncompetitive antagonist of the NMDA receptor channel that is safe for use in young girls with Rett syndrome. Preliminary evidence suggests that dextromethorphan may improve some core features of Rett syndrome. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that dextromethorphan at various doses does not change EEG spike counts over 6 months, though precision was limited to exclude an important effect.

Evaluation of QTc in Rett syndrome: Correlation with age, severity, and genotype.

Rett syndrome (RTT) is caused by MECP2 mutations, resulting in various neurological symptoms. Prolonged corrected QT interval (QTc) is also reported and is a speculated cause of sudden death in RTT. The purpose of this study was to correlate QTc in RTT patients with age, clinical severity, and genotype. 100 RTT patients (98 females, 2 males) with MECP2 mutations underwent baseline neurological evaluation (KKI-RTT Severity Scale) and QTc measurement (standard 12 lead electrocardiogram) as part of our prospective natural history study. Mean QTc of the cohort was 422.6 msec, which did not exceed the normal values for age. 7/100 patients (7%) had QTc prolongation (>450 msec). There was a trend for increasing QTc with age and clinical severity (P = 0.09). No patients with R106C, R106W, R133C, R168*, R270*, R294*, R306C, R306H, and R306P mutations demonstrated QTc prolongation. There was a relatively high proportion of QTc prolongation in patients with R255* mutations (2/8, 25%) and large deletions (1/4, 25%). The overall presence of QTc prolongation did not correlate with mutation category (P = 0.52). Our findings demonstrate that in RTT, the prevalence of QTc prolongation is lower than previously reported. Hence, all RTT patients warrant baseline ECG; if QTc is prolonged, then cardiac followup is warranted. If initial QTc is normal, then annual ECGs, particularly in younger patients, may not be necessary. However, larger sample sizes are needed to solidify the association between QTc and age and clinical severity. The biological and clinical significance of mild QTc prolongation above the normative data remains undetermined.

Bone health in facioscapulohumeral muscular dystrophy: A cross-sectional study.

INTRODUCTION: Herein we provide a comprehensive overview of bone health in facioscapulohumeral muscular dystrophy (FSHD). METHODS: Ninety-four adult individuals with FSHD type 1 from 2 sites were included in this cross-sectional study. Clinical characteristics and determinants of bone health were examined. Relationships between bone mineral density (BMD), strength, and function were explored. RESULTS: Nearly a third of subjects were deficient in vitamin D3 . Mean whole-body BMD z-score was -0.7; 11% of subjects had greater than age-related reductions in whole-body BMD (z-score < -2.0). Whole-body and regional BMDs were associated with strength and function. Thirty-six percent had a history of fractures. Likelihood of fractures was reduced for those with normal whole-body BMD (odds ratio = 0.25, 95% confidence interval 0.04-0.78). DISCUSSION: A diagnosis of FSHD is not necessarily predictive of reduced BMD or increased fracture rate. Given the considerable variability of bone health in the FSHD population, strength and function can serve as predictors of BMD. Muscle Nerve 56: 1108-1113, 2017.

Functional outcomes in Rett syndrome.

AIM: To relate functional outcomes to mutation type and age at evaluation in patients with Rett syndrome (RTT). METHOD: We identified 96 RTT patients with mutations in the MECP2 (methyl-CpG-binding protein 2) gene. Chart analysis, clinical evaluation, and functional measures were completed. RESULTS: Among 11 mutation groups, a statistically significant group effect of mutation type was observed for self-care, upper extremity function, and mobility, on standardized measures administered by occupational and physical therapists. Patients with R133C and uncommon mutations tended to perform best on upper extremity and self-care items, whereas patients with R133C, R306C and R294X had the highest scores on the mobility items. The worst performers on upper extremity and self-care items were patients with large deletions, R255X, R168X, and T158M mutations. The lowest scores for mobility were found in patients with T158M, R255X, R168X, and R270X mutations. On categorical variables as reported by parents at the time of initial evaluation, patients with R133C and R294X were most likely to have hand use, those with R133C, R294X, R306C and small deletions were most likely to be ambulatory, and those with R133C were most likely to be verbal. INTERPRETATION: Functional performance in RTT patients may relate to the type of mutation. Knowledge of these relationships is useful for developing appropriate rehabilitation strategies and prognosis.

Sildenafil does not improve cardiomyopathy in Duchenne/Becker muscular dystrophy.

OBJECTIVE: Duchenne and Becker muscular dystrophies (DBMD) are allelic disorders caused by mutations in dystrophin. Adults with DBMD develop life-threatening cardiomyopathy. Inhibition of phosphodiesterase 5 (PDE5) improves cardiac function in mouse models of DBMD. To determine whether the PDE5-inhibitor sildenafil benefits human dystrophinopathy, we conducted a randomized, double-blind, placebo-controlled trial (ClinicalTrials.gov, number NCT01168908). METHODS: Adults with DBMD and cardiomyopathy (ejection fraction ≤ 50%) were randomized to receive sildenafil (20mg 3× daily) or placebo for 6 months. All subjects received an additional 6 months of open-label sildenafil. The primary endpoint was change in left ventricular end-systolic volume (LVESV) on cardiac magnetic resonance imaging. Secondary cardiac endpoints, skeletal muscle function, and quality of life were also assessed. RESULTS: An interim analysis (performed after 15 subjects completed the blinded phase) revealed that 29% (4 of 14) of subjects had a ≥10% increase in LVESV after 6 months of sildenafil compared to 13% (1 of 8) of subjects receiving placebo. Subjects with LVESV > 120ml at baseline were more likely to worsen at 12 months regardless of treatment assignment (p = 0.035). Due to the higher number of subjects worsening on sildenafil, the data and safety monitoring board recommended early termination of the study. There were no statistically significant differences in outcome measures between treatment arms. INTERPRETATION: Due to the small sample size, comparisons between groups must be interpreted with caution. However, this trial suggests that sildenafil is unlikely to improve cardiac function in adults with DBMD.

Transcriptional profiling in facioscapulohumeral muscular dystrophy to identify candidate biomarkers.

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive neuromuscular disorder caused by contractions of repetitive elements within the macrosatellite D4Z4 on chromosome 4q35. The pathophysiology of FSHD is unknown and, as a result, there is currently no effective treatment available for this disease. To better understand the pathophysiology of FSHD and develop mRNA-based biomarkers of affected muscles, we compared global analysis of gene expression in two distinct muscles obtained from a large number of FSHD subjects and their unaffected first-degree relatives. Gene expression in two muscle types was analyzed using GeneChip Gene 1.0 ST arrays: biceps, which typically shows an early and severe disease involvement; and deltoid, which is relatively uninvolved. For both muscle types, the expression differences were mild: using relaxed cutoffs for differential expression (fold change ≥1.2; nominal P value <0.01), we identified 191 and 110 genes differentially expressed between affected and control samples of biceps and deltoid muscle tissues, respectively, with 29 genes in common. Controlling for a false-discovery rate of <0.25 reduced the number of differentially expressed genes in biceps to 188 and in deltoid to 7. Expression levels of 15 genes altered in this study were used as a "molecular signature" in a validation study of an additional 26 subjects and predicted them as FSHD or control with 90% accuracy based on biceps and 80% accuracy based on deltoids.

Correlation of the vesicular acetylcholine transporter densities in the striata to the clinical abilities of women with Rett syndrome.

Rett syndrome (RTT) is a neurodevelopmental disability characterized by mutations in the X-linked methyl-CpG-binding protein 2 located at the Xq28 region. The severity is modified in part by X chromosomal inactivation resulting in wide clinical variability. We hypothesized that the ability to perform the activities of daily living (ADL) is correlated with the density of vesicular acetylcholine transporters in the striata of women with RTT. The density of the vesicular acetylcholine transporters in the living human brain can be estimated by single-photon emission-computed tomography (SPECT) after the administration of (-)-5-[¹²³I]iodobenzovesamicol ([¹²³I]IBVM). Twenty-four hours following the intravenous injection of ∼333 MBq (9 mCi) [¹²³ I]IBVM, four women with RTT and nine healthy adult volunteer control participants underwent SPECT brain scans for 60 min. The Vesicular Acetylcholine Transporter Binding Site Index (Kuhl et al., 1994), a measurement of the density of vesicular acetylcholine transporters, was estimated in the striatum and the reference structure, the cerebellum. The women with RTT were assessed for certain ADL. Although the striatal Vesicular Acetylcholine Transporter Binding Site Index was not significantly lower in RTT (5.2 ± 0.9) than in healthy adults (5.7 ± 1.6), RTT striatal Vesicular Acetylcholine Transporter Binding Site Indices and ADL scores were linearly associated (ADL = 0.89*(Vesicular Acetylcholine Transporter Binding Site Index) + 4.5; R² = 0.93; P < 0.01), suggesting a correlation between the ability to perform ADL and the density of vesicular acetylcholine transporters in the striata of women with RTT. [¹²³I]IBVM is a promising tool to characterize the pathophysiological mechanisms of RTT and other neurodevelopmental disabilities.

A unique library of myogenic cells from facioscapulohumeral muscular dystrophy subjects and unaffected relatives: family, disease and cell function.

To explore possible mechanisms of pathology in facioscapulohumeral muscular dystrophy (FSHD), we generated a novel library of myogenic cells composed of paired cultures derived from FSHD subjects and unaffected first-degree relatives. We prepared cells from biopsies of both biceps and deltoid muscles obtained from each of 10 FSHD and 9 unaffected donors. We used this new collection to determine how family background and disease affected patterns of growth and differentiation, expression of a panel of candidate, and muscle-specific genes, and responses to exogenous stressors. We found that FSHD and unaffected cells had, on average, indistinguishable patterns of differentiation, gene expression, and dose-response curves to staurosporine, paraquat, hydrogen peroxide, and glutathione depletion. Differentiated FSHD and unaffected cultures were both more sensitive to glutathione depletion than proliferating cultures, but showed similar responses to paraquat, staurosporine, and peroxide. For stress responses, the sample size was sufficient to detect a 10% change in effect at the observed variability with a power of >99%. In contrast, for each of these properties, we found significant differences among cells from different cohorts, and these differences were independent of disease status, gender, or muscle biopsied. Thus, though none of the properties we examined could be used to reliably distinguish between FSHD and unaffected cells, family of origin was an important contributor to gene-expression patterns and stressor responses in cultures of both FSHD and unaffected myogenic cells.

X-linked adrenoleukodystrophy: ABCD1 de novo mutations and mosaicism.

X-linked adrenoleukodystrophy (X-ALD) is a progressive peroxisomal disorder affecting adrenal glands, testes and myelin stability that is caused by mutations in the ABCD1 (NM_000033) gene. Males with X-ALD may be diagnosed by the demonstration of elevated very long chain fatty acid (VLCFA) levels in plasma. In contrast, only 80% of female carriers have elevated plasma VLCFA; therefore targeted mutation analysis is the most effective means for carrier detection. Amongst 489 X-ALD families tested at Kennedy Krieger Institute, we identified 20 cases in which the ABCD1 mutation was de novo in the index case, indicating that the mutation arose in the maternal germ line and supporting a new mutation rate of at least 4.1% for this group. In addition, we identified 10 cases in which a de novo mutation arose in the mother or the grandmother of the index case. In two of these cases studies indicated that the mothers were low level gonosomal mosaics. In a third case biochemical, molecular and pedigree analysis indicated the mother was a gonadal mosaic. To the best of our knowledge mosaicism has not been previously reported in X-ALD. In addition, we identified one pedigree in which the maternal grandfather was mosaic for the familial ABCD1 mutation. Less than 1% of our patient population had evidence of gonadal or gonosomal mosaicism, suggesting it is a rare occurrence for this gene and its associated disorders. However, the residual maternal risk for having additional ovum carrying the mutant allele identified in an index case that appears to have a de novo mutation is at least 13%.

Ocular MECP2 protein expression in patients with and without Rett syndrome.

Rett syndrome is a neurodevelopmental disorder caused by mutations in the methyl CpG binding protein 2 gene (MECP2). The MECP2 protein is expressed primarily in neurons, and mutations in the gene lead to the clinical features of Rett syndrome in human patients and neurologic deficits in murine models. Visual function is relatively preserved in Rett syndrome patients, but the cause is unknown. The eyes of two Rett syndrome patients who died of the disease were analyzed; no gross or microscopic changes were found. MECP2 expression was examined using immunohistochemistry; nuclear protein expression was largely limited to ganglion cells and the portion of the inner nuclear layer populated by amacrine cells. No significant differences in MECP2 protein level or distribution were identified in the two eyes from the Rett syndrome patients, compared with 11 controls. The findings were compared with MECP2 expression in the brain of these two subjects and in MECP2-deficient mice. The findings suggest that the normally limited expression of MECP2 in visual pathway neurons may underlie the intact vision observed in Rett syndrome.

Bone mass in Rett syndrome: association with clinical parameters and MECP2 mutations.

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in the MECP2 gene. In 49 female RTT children, aged 1.9-17 y, bone mass was assessed and correlated with clinical parameters and mutations involving the MECP2 gene. We also studied five adult females, aged 20-33 y, and one male child, aged 6 y. Lumbar spine bone mineral content (BMC) and bone mineral density (BMD) were correlated with weight, height, BMI, clinical severity, degree of scoliosis, use of anticonvulsants, and ambulatory status. L1-L4 BMD and BMC showed that 48.9% of them had BMD values >2 SD below age-related norms. BMD values were in the osteoporotic range in the five adult females with RTT. Eleven percent of the children and adults with RTT experienced fractures. Low bone mass was correlated with marginal significance to clinical severity and ambulation but not to scoliosis or anticonvulsant use. Lowest bone mass occurred in patients with T158M or R270X mutations but without statistical significance. Studies in a murine model of RTT confirmed low bone mass as an inherent component of this syndrome. MECP2 mutations and clinical parameters impact bone mass in RTT, but an association with a specific mutation was not demonstrable.

Effects of sedation on auditory brainstem response in Rett syndrome.

Prolongation of the I-V interpeak latency intervals have been reported in Rett syndrome and other neurodevelopmental disorders. It has been suggested that the use of sedation may account for differences in the interpeak latency intervals when comparisons are made across diagnostic groups if sedated control groups are not used for the basis of comparison. This study examined the effects of sedation on auditory brainstem response interpeak latency intervals (i.e., I-III, III-V, and I-V) in two groups: (1) a group with Rett syndrome who were positive for mutations in the MECP2 gene and (2) a group negative for mutations in the MECP2 gene but who were severely to profoundly delayed with other causes of mental retardation. To further assess the effects of sedation, a third group of sedated and nonsedated female participants, taken from an in-house normative auditory brainstem response database was also included. An analysis of variance indicated (1) longer I-V interpeak latency intervals in the sedated participants with Rett syndrome; (2) longer III-V interpeak latency intervals in the mutation-positive participants as compared to non-Rett syndrome, mutation-negative participants; and (3) no significant effects of sedation on the I-III, III-V, or I-V interpeak latency intervals among the normative group participants, according to t tests. The findings suggest a possible biological basis for the discrepancy in the literature on auditory brain stem responses in Rett syndrome, and warrant cautious interpretation of auditory brainstem responses findings in sedated subjects with Rett syndrome, as well as in those with mental retardation and seizures.

Brain metabolism in Rett syndrome: age, clinical, and genotype correlations.

OBJECTIVE: Brain metabolism, as studied by magnetic resonance spectroscopy (MRS), has been previously shown to be abnormal in Rett syndrome (RTT). This study reports the relation of MRS findings to age, disease severity, and genotype. METHODS: Forty RTT girls (1-14 years old) and 12 age-matched control subjects were examined. Single-voxel proton MRS of left frontal white matter was performed. RESULTS: NAA/Cr ratios decreased and myoinositol/Cr ratios increased with age in RTT patients (both p < 0.03), whereas these ratios were stable in control. The mean glutamate and glutamine/Cr ratio was 36% greater in RTT patients than in control (p = 0.043). The mean NAA/Cr ratio was 12.6% lower in RTT patients with seizures compared with those without seizures (p = 0.017). NAA/Cr ratios decreased with increasing clinical severity score (p = 0.031). Compared with patients with T158X, R255X, and R294X mutations, and C-terminal deletions, patients with the R168X mutation tended to have the greatest severity score (0.01 < or = p < or = 0.11) and the lowest NAA/Cr ratio (0.029 < or = p < 0.14). INTERPRETATION: Decreasing NAA/Cr and increasing myoinositol/Cr with age are suggestive of progressive axonal damage and astrocytosis in RTT, respectively, whereas increased glutamate and glutamine/Cr ratio may be secondary to increasing glutamate/glutamine cycling at the synaptic level. The relations between NAA/Cr, presence or absence of seizures, and disease severity suggest that MRS provides a noninvasive measure of cerebral involvement in RTT.

Progressive cavitating leukoencephalopathy: a novel childhood disease.

We report 19 patients with a previously undelineated neurodegenerative syndrome characterized by episodic acute onset of irritability or neurological deficits between 2 months and 3.5 years of age, followed by steady or intermittent clinical deterioration. Seven children died between 11 months and 14 years of age. Cranial magnetic resonance imaging (MRI) shows patchy leukoencephalopathy with cavities, and vascular permeability, in actively affected regions. Early lesions affect corpus callosum and centrum semiovale, with or without cerebellar or cord involvement. After repeated episodes, areas of tissue loss coalesce with older lesions to become larger cystic regions in brain or spinal cord. Diffuse spasticity, dementia, vegetative state, or death ensues. Gray matter is spared until late in the course. In some, incomplete clinical or MRI recovery occurs after episodes. The clinical course varies from rapid deterioration to prolonged periods of stability that are unpredictable by clinical or MRI changes. Elevated levels of lactate in brain, blood, and cerebrospinal fluid, abnormal urine organic acids, and changes in muscle respiratory chain enzymes are present but inconsistent, without identifiable mitochondrial DNA mutations or deletions. Pathological studies show severe loss of myelin sparing U-fibers, axonal disruption, and cavitary lesions without inflammation. Familial occurrence and consanguinity suggest autosomal recessive inheritance of this distinct entity.

Histone modifications in Rett syndrome lymphocytes: a preliminary evaluation.

Most cases of Rett syndrome (RTT) are associated with mutations in the coding region of the transcriptional regulator MeCP2. This gene appears to repress gene expression through chromatin conformational changes secondary to histone modifications, mainly histone deacetylation of core histones H3 and H4. There is limited and contradictory information about histone modifications in RTT tissues. The present study intended to provide a preliminary characterization of histone acetylation (AcH3, AcH4) and methylation (MeH3) in RTT, with emphasis on non-selected peripheral cells and molecular-neurologic correlations. We compared 17 females with RTT, 11 of them with MeCP2 mutations, with 10 gender-matched controls in terms of lymphocyte lysate immunoblotting-based levels. We found that immunoreactivities for MeCP2 and AcH3/AcH4 are variable in both control and RTT subjects. Despite this variability, RTT subjects with nonsense mutations showed the expected reduction in C-terminal MeCP2 immunoreactivity. Regardless of MeCP2 levels, both subjects with (RTTPos) and without (RTTNeg) mutations had decreased levels of AcH3. The latter reductions were mainly driven by decreases in levels of H3 acetylated at lysine residue 14 (AcH3K14) and independent of parallel, but milder, decreases in immunoreactivity for MeH3 lysine residues (MeH3K4/MeH3K9). Within our study sample, reductions in AcH3 were correlated with severity of head growth deceleration in the RTTPos group. This contrasted with the lack of significant association between location of MeCP2 mutation and severity of the RTT neurologic phenotype. We concluded that there were distinctive profiles of histone acetylation/methylation in RTT peripheral cells, which reflect pathogenetic mechanisms common to subjects with clinical features of this disorder, regardless of mutation status, and that these patterns may be relevant to neurologic dysfunction in RTT.

Clinical variability in Rett syndrome.

The clinical variability of Rett syndrome, associated with mutations in the MECP2 gene, varies from classically symptomatic female patients to asymptomatic female patients, and male patients who have none of the diagnostic features considered pathognomonic of this disease. Multiple factors contribute to this variability. In our studies, mutations closer to the amino-terminus, prior to amino acid 255, led to severe clinical manifestations, such as inability to walk, severe dysphagia, and urinary organic acid abnormalities, compared with mutations toward the carboxyl-terminus. However, we found no correlation between severity and mutation type (missense versus nonsense). Despite the importance of mutation location to clinical severity, the widely varying severity within the same mutation suggests that in females, X-chromosome inactivation or other epigenetic phenomena also have roles in determining severity. We propose that stages 1 and 2 of the disease are a consequence of failed, time-linked, postnatal expression of MeCP2 in cerebellar neurons. This, in association with glutamate N-methyl-D-aspartate receptor-mediated neuroexcitotoxic injury to the differentiating neurons, results in the transient age-specific autistic-like behavior, motor, and cognitive dysfunction associated with these stages.