Search PubMed⌕ Search

Biomedical subjects

J R Mendell

Publications and source records attributed to J R Mendell.

At least 55 records · Page 3Linked to original sources
PubMed1998

Intragenic telSMN mutations: frequency, distribution, evidence of a founder effect, and modification of the spinal muscular atrophy phenotype by cenSMN copy number.

The autosomal recessive neuromuscular disorder proximal spinal muscular atrophy (SMA) is caused by the loss or mutation of the survival motor neuron (SMN) gene, which exists in two nearly identical copies, telomeric SMN (telSMN) and centromeric SMN (cenSMN). Exon 7 of the telSMN gene is homozygously absent in approximately 95% of SMA patients, whereas loss of cenSMN does not cause SMA. We searched for other telSMN mutations among 23 SMA compound heterozygotes, using heteroduplex analysis. We identified telSMN mutations in 11 of these unrelated SMA-like individuals who carry a single copy of telSMN: these include two frameshift mutations (800ins11 and 542delGT) and three missense mutations (A2G, S262I, and T274I). The telSMN mutations identified to date cluster at the 3' end, in a region containing sites for SMN oligomerization and binding of Sm proteins. Interestingly, the novel A2G missense mutation occurs outside this conserved carboxy-terminal domain, closely upstream of an SIP1 (SMN-interacting protein 1) binding site. In three patients, the A2G mutation was found to be on the same allele as a rare polymorphism in the 5' UTR, providing evidence for a founder chromosome; Ag1-CA marker data also support evidence of an ancestral origin for the 800ins11 and 542delGT mutations. We note that telSMN missense mutations are associated with milder disease in our patients and that the severe type I SMA phenotype caused by frameshift mutations can be ameliorated by an increase in cenSMN gene copy number.

Alleles↗
PubMed1998

Fate of Schwann cells in CMT1A and HNPP: evidence for apoptosis.

The fate of Schwann cells in Charcot-Marie-Tooth (CMT) neuropathies was addressed in this study of nerve biopsies from patients with proven PMP22 duplications and deletions. In frozen sections, apoptotic nuclei were detected using the TUNEL method. In adjacent sections, anti-neurofilament 68kD antibody was used as an axonal marker, while the antibodies to NKH-1 and low-affinity nerve growth factor receptor P75NTR were used as Schwann cell markers. In addition, plastic sections were used to determine the densities of myelinated fibers and Schwann cell nuclei. In all biopsies from CMT1A, TUNEL-positive nuclei appeared in clusters. In adjacent sections, areas of TUNEL-positive nuclei matched with areas devoid of neurofilaments and NKH-1-positive Schwann cell silhouettes, suggesting that the apoptotic nuclei belonged to nonmyelinating Schwann cells. In addition, quantitative studies on plastic-embedded sections showed a significantly reduced number of total Schwann cells compared with controls, strongly favoring a loss of Schwann cell by apoptosis. In HNPP, the number of total Schwann cells was increased and a significant Schwann cell apoptosis was observed in only 2 patients. Examination of plastic sections and teased nerve preparations from these cases suggested that the Schwann cell apoptosis might be related to the regenerative state of the nerve resulting from the process of sprout pruning. No strict correlation between p75NTR expression and apoptosis was found. These studies indicate that factors regulating Schwann cell number in early postnatal development continue to be important for Schwann cell survival throughout life.

Adult↗
PubMed1998

Congenital muscular dystrophy with complete laminin-alpha2-deficiency, cortical dysplasia, and cerebral white-matter changes in children.

Congenital muscular dystrophy consists of Fukuyama congenital muscular dystrophy, Walker-Warburg syndrome, muscle-eye-brain disease, and occidental congenital muscular dystrophy, which is further divided into laminin-alpha2-positive and laminin-alpha2-negative subgroups. These forms of congenital muscular dystrophy are frequently associated with abnormal white-matter changes, whereas the Fukuyama form, Walker-Warburg syndrome, and muscle-eye-brain disease are also frequently found to have polymicrogyria. We now report two infants with complete laminin-alpha2-deficiency who have not only abnormal cerebral white-matter lesions, but also bioccipital polymicrogyria. There are significant similarities in the clinical and cerebral manifestations among the various types of congenital muscular dystrophy. The diagnosis of the Fukuyama form, laminin-alpha2-deficiency, Walker-Warburg syndrome, and muscle-eye-brain disease cannot always be established on radiological studies alone.

Brain↗
PubMed1998

Pilot trial of albuterol in facioscapulohumeral muscular dystrophy. FSH-DY Group.

BACKGROUND/OBJECTIVE: Facioscapulohumeral muscular dystrophy (FSHD) is currently untreatable, and there have been few therapeutic trials of any agent in the disease. Animal studies have demonstrated that beta2-adrenergic agonists induce muscle hypertrophy and prevent atrophy after a variety of physical and biochemical insults, and two human studies have shown that these agents increase certain measures of strength in healthy volunteers. We conducted an open-label pilot trial of a beta2-agonist (albuterol) in patients with FSHD. METHODS: Fifteen FSHD patients were given sustained-release albuterol (16.0 mg/day) for 3 months. The primary outcome measure was lean body mass, which was assessed through dual energy X-ray absorptiometry (DEXA). Strength was evaluated through maximal voluntary isometric contraction testing (MVICT) and manual muscle testing. RESULTS: Albuterol significantly increased DEXA lean body mass (the skeletal muscle compartment) by 1.29 +/- 1.18 kg (mean +/- SD, p = 0.001). Strength assessed through composite MVICT scores also increased by an average of 0.33 +/- 0.60 (p = 0.05), representing an overall 12% improvement in strength. CONCLUSIONS: These encouraging results suggest that beta2-agonists may have a role in treating FSHD and possibly other neuromuscular diseases. The effects of albuterol in FSHD are currently being evaluated in a larger, randomized, double-blind, placebo-controlled trial lasting 1 year.

Absorptiometry, Photon↗
PubMed1997

Deletion and conversion in spinal muscular atrophy patients: is there a relationship to severity?

The spinal muscular atrophy-determining gene, survival motor neuron (SMN), is present in two copies, telSMN and cenSMN, which can be distinguished by base-pair changes in exons 7 and 8. The telSMN gene is often absent in spinal muscular atrophy patients, which could be due to deletion or sequence conversion (telSMN conversion to cenSMN giving rise to two cenSMN genes). To test for conversion events in spinal muscular atrophy, we amplified a 1-kb fragment that spanned exons 7 and 8 of SMN from 5 patients who retained telSMN exon 8 but lacked exon 7. In all patients, sequence analysis demonstrated that cenSMN exon 7 was adjacent to telSMN exon 8, indicating conversion. All 5 patients with this mutation had type II or III spinal muscular atrophy, strongly supporting an association with chronic spinal muscular atrophy. We also identified 3 families in which 2 siblings had no detectable telSMN but presented with markedly different phenotypes. We suggest that sequence conversion is a common event in spinal muscular atrophy and is associated with the milder form of the disease. The severity, however, can be modified in either a positive or negative direction by other factors that influence splicing or expression of the sequence converted SMN gene.

Base Sequence↗
PubMed1997

Genotype-phenotype correlations of DHP receptor alpha 1-subunit gene mutations causing hypokalemic periodic paralysis.

Hypokalemic periodic paralysis (hypoKPP) is an autosomal dominant or sporadic disorder characterized by periodic, reversible attacks of muscle weakness. Mutations in the skeletal muscle dihydropyridine receptor alpha 1-subunit that functions as a calcium channel (CACNL1A3) cause hypoKPP. We studied a group of 45 hypoKPP probands and demonstrated mutations in 30 of them. When compared with patients in whom CACNL1A3 mutations were not identified, those with mutations had an earlier age of onset and more often had a family history of hypoKPP. To date, three mutations have been identified. The R1239G mutation has only been found in one family. Of the 30 probands with recognized mutations, R528H accounted for 43% and R1239H was seen in 53%. Age of onset and potassium levels during attacks were lower in patients with the R1239H mutation than those with R528H. Cardiac dysrhythmias co-segregated with hypoKPP in one small kindred with the R528H mutation. No mutations were identified in exons of the gene encoding the S4 segments of domains one and three or the cytoplasmic loop between domains two and three. In addition to the 45 hypoKPP probands, an additional 11 probands with clinical variants of hypoKPP (three thyrotoxic hypoKPP and eight Andersen syndrome patients) were examined for CACNL1A3 mutations and none were found.

Adolescent↗
PubMed1997

Identification of proximal spinal muscular atrophy carriers and patients by analysis of SMNT and SMNC gene copy number.

The survival motor neuron (SMN) transcript is encoded by two genes, SMNT and SMNC. The autosomal recessive proximal spinal muscular atrophy that maps to 5q12 is caused by mutations in the SMNT gene. The SMNT gene can be distinguished from the SMNC gene by base-pair changes in exons 7 and 8. SMNT exon 7 is not detected in approximately 95% of SMA cases due to either deletion or sequence-conversion events. Small mutations in SMNT now have been identified in some of the remaining nondeletion patients. However, there is no reliable quantitative assay for SMNT, to distinguish SMA compound heterozygotes from non-5q SMA-like cases (phenocopies) and to accurately determine carrier status. We have developed a quantitative PCR assay for the determination of SMNT and SMNC gene-copy number. This report demonstrates how risk estimates for the diagnosis and detection of SMA carriers can be modified by the accurate determination of SMNT copy number.

Amino Acid Sequence↗
PubMed1997

The survival motor neuron protein in spinal muscular atrophy.

The 38 kDa survival motor neuron (SMN) protein is encoded by two ubiquitously expressed genes: telomeric SMN (SMN(T)) and centromeric SMN (SMN(C)). Mutations in SMN(T), but not SMN(C), cause proximal spinal muscular atrophy (SMA), an autosomal recessive disorder that results in loss of motor neurons. SMN is found in the cytoplasm and nucleus. The nuclear form is located in structures termed gems. Using a panel of anti-SMN antibodies, we demonstrate that the SMN protein is expressed from both the SMN(T) and SMN(C) genes. Western blot analysis of fibroblasts from SMA patients with various clinical severities of SMA showed a moderate reduction in the amount of SMN protein, particularly in type I (most severe) patients. Immunocytochemical analysis of SMA patient fibroblasts indicates a significant reduction in the number of gems in type I SMA patients and a correlation of the number of gems with clinical severity. This correlation to phenotype using primary fibroblasts may serve as a useful diagnostic tool in an easily accessible tissue. SMN is expressed at high levels in brain, kidney and liver, moderate levels in skeletal and cardiac muscle, and low levels in fibroblasts and lymphocytes. In SMA patients, the SMN level was moderately reduced in muscle and lymphoblasts. In contrast, SMN was expressed at high levels in spinal cord from normals and non-SMA disease controls, but was reduced 100-fold in spinal cord from type I patients. The marked reduction of SMN in type I SMA spinal cords is consistent with the features of this motor neuron disease. We suggest that disruption of SMN(T) in type I patients results in loss of SMN from motor neurons, resulting in the degeneration of these neurons.

Animals↗
PubMed1997

A pilot trial of prednisone in facioscapulohumeral muscular dystrophy. FSH-DY Group.

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant, 4q35-linked, slowly progressive muscular dystrophy with no known effective treatment. Since prednisone improves strength in Duchenne dystrophy, we performed a pilot, open-label trial of prednisone in eight subjects fulfilling strict diagnostic criteria for FSHD. Prednisone (1.5 mg/kg/day; maximum 80 mg/day) was administered for 12 weeks. Manual muscle testing, maximum voluntary isometric contraction testing, and muscle mass estimations by dual energy x-ray absorptiometry and urinary creatinine excretion were performed at baseline and at 12 weeks. There were no significant changes in strength or muscle mass. We conclude that prednisone given for 12 weeks does not produce major improvement in strength or increase muscle mass in FSHD. The study did not have sufficient power or length of follow-up to address the possibility that prednisone might arrest or slow disease progression.

Adolescent↗
PubMed1997

Dystrophin expression in a Duchenne muscular dystrophy patient with a frame shift deletion.

The exon 45 deletion is a common dystrophin gene deletion. Although this is an out-of-frame deletion, which should not allow for protein synthesis, it has been observed in mildly affected patients. We describe a patient with an exon 45 deletion who produced protein, but still had a severe Duchenne muscular dystrophy phenotype. RT-PCR analysis and cDNA sequencing from the muscle biopsy sample revealed that the exon 45 deletion induced exon skipping of exon 44, which resulted in an in-frame deletion and the production of dystrophin. A conformational change in dystrophin induced by the deletion is proposed as being responsible for the severe phenotype in the patient. We feel that the variable clinical phenotype observed in patients with the exon 45 deletion is not due to exon splicing but may be the result of other environmental or genetic factors, or both.

Base Sequence↗
PubMed1997

Quality improvement in neurology residency programs. Report of the Quality Improvement Committee of the Association of University Professors of Neurology.

The neurology residency programs in the United States are facing a crisis of quality. The Association of University Professors of Neurology (AUPN) approved the Quality Improvement Committee to examine this situation and make recommendations, which have been accepted by the AUPN. The recommendations are (1) that the educational goals of neurology residency training be dissociated from patient-care needs in academic medical centers and (2) that minimum levels of quality be applied to residents in neurology residency programs and to these programs themselves. These minimum criteria should include minimum educational criteria for entry into the program, minimum criteria for advancement from one year to the next in the program, and minimum criteria for performance of the graduates of neurology residency programs for program accreditation. The implementation of these recommendations will require a shift of funding of the care of indigent patients from the graduate medical education budget to direct patient-care sources. These recommendations will significantly improve the quality of neurologists and neurologic care in the United States.

Academic Medical Centers↗
PubMed1996

Multiple mitochondrial DNA deletions in sporadic inclusion body myositis: a study of 56 patients.

Inclusion body myositis, a chronic inflammatory disorder, is the most common cause of myopathy in adults over the age of 50. Diagnosis is based on clinical features and distinctive morphological findings by both light and electron microscopy. The causes of inclusion body myositis are still unknown. Ultrastructural mitochondrial changes and ragged-red fibers are common in patients with sporadic inclusion body myositis, and multiple [correction of mutiple] mitochondrial DNA (mtDNA) deletions have been reported in 3 such patients, suggesting that mtDNA mutations may have a pathogenetic role. We studied 56 patients with sporadic inclusion body myositis, using a combination of clinical, morphological, biochemical, and molecular genetic analyses to determine the frequency and the distribution of mtDNA deletions. Using the polymerase chain reaction, we found multiple mtDNA deletions in 73% of patients, compared to 40% of normal age-matched control subjects and 47% of disease control subjects. The presence of deletions correlated with morphological evidence of ragged-red, cytochrome c oxidase-negative fibers, and with defects of complexes I and IV of the electron transport chain. Although aging may account for a proportion of mtDNA deletions in patients with sporadic inclusion body myositis and control subjects, mtDNA alterations may be accelerated in sporadic inclusion body myositis.

Adult↗
PubMed1996

Neuropathies associated with monoclonal gammopathies.

Approximately 10% of patients with idiopathic peripheral neuropathy have an associated serum monoclonal gammopathy or M-protein. This represents six times the incidence of M-proteins found in the general population. In 5% of idiopathic peripheral neuropathy patients the M-protein is associated with an identifiable plasma cell dyscrasia. Sclerotic myeloma is particularly important to recognize because treatment may result in amelioration of the neuropathy and remission of the tumor. Patients with primary systemic amyloidosis often have preferential small fiber involvement with a dissociated sensory loss and autonomic dysfunction. The nerve root infiltration of lymphoproliferative disorders may simulate a polyradiculoneuropathy. In cases without an identifiable cause for the M-protein, referred to as monoclonal gammopathy of undetermined significance (MGUS), the pathophysiologic basis for the neuropathy is poorly defined in most cases. A role for M-proteins with antibody activity to myelin-associated glycoprotein is provocative. This review summarizes current knowledge of this important group of disorders.

Humans↗
PubMed1996

An 11 base pair duplication in exon 6 of the SMN gene produces a type I spinal muscular atrophy (SMA) phenotype: further evidence for SMN as the primary SMA-determining gene.

The gene for autosomal recessive spinal muscular atrophy (SMA) has been mapped to 5q12 in a region that contains repeated markers and genes. Three cDNAs that detect deletions in SMA patients have been reported. One of these, the survival motor neuron (SMN) cDNA, is encoded by two genes (SMNT and SMNC) which are distinguished by base changes in exons 7 and 8. Exon 7 of the SMNT gene is not detectable in approximately 95% of SMA cases, due either to deletion or sequence conversion. There is limited information on the mutations in SMA patients that have detectable SMNT, these are critical for confirmation of SMNT as the SMA gene. Using SSCP analysis of the SMN exons we screened our SMA patients that possess at least one intact SMNT allele for mutations in SMNT. We identified one type I SMA patient with an 11 bp duplication in exon 6 which causes a frameshift and premature termination of the deduced SMNT protein. Dosage and SSCP analysis of SMNT in this family indicated that the father contributed a SMNT-deleted allele to the affected child whereas the mother passed on the 11 bp exon 6 duplication SMNT allele. Analysis of RNA by RT-PCR conclusively demonstrated that the 11 bp duplication is associated with the SMNT locus and not SMNC. This mutation provides strong support for SMN as the SMA-determining gene and indicates that disruption of SMNT on its own is sufficient to produce a severe type I SMA phenotype.

Alleles↗
PubMed1996

The immunopathogenic role of complement in human muscle disease.

The complement system has been shown to play a pathogenic role in only a small number of muscle diseases. A complement-induced microangiopathy is important in dermatomyositis and in the rare disorder, necrotizing myopathy with pipestem capillaries. Recent studies demonstrate the reversibility of microvascular damage in dermatomyositis by intravenous immune globulin which appears to intercept the assembly and deposition of membrane attach complex. In myasthenia gravis, complement-mediated lysis directed at the acetylcholine receptor leads to a cascade of events reducing the number of receptors, simplifying the complex architecture of the junctional folds and decreasing the available surface for the insertion of new receptors. The newest condition in which a role for complement has been demonstrated is X-linked vacuolated myopathy. The condition is of interest because membrane attack complex deposits result in shedding of complement-laden membrane fragments in contrast to a cytolytic process as the consequence of assembly of the terminal complement components.

Complement System Proteins↗
PubMed1996

A novel splice site mutation in a Becker muscular dystrophy patient.

A Becker muscular dystrophy patient was found to have a single base substitution at the 5' end of intron 54. This single base substitution disrupts the invariant GT dinucleotide within the 5' donor splice site and was shown to cause an out of frame deletion of exon 54 during mRNA processing. This is predicted to produce a truncated dystrophin protein which is more consistent with a DMD phenotype. However, small quantities of normal mRNA are also transcribed and these are sufficient to produce a reduced amount of normal molecular weight dystrophin and give rise to a milder BMD phenotype. This indicates that a single base substitution at an invariant dinucleotide of the splice site consensus sequence may still allow read through of the message and allow the production of some normal protein. This shows that there are a greater number of possible intronic mutations that can lead to a mild phenotype and it also underlines the importance of performing cDNA analysis when screening for small gene alterations in the BMD patient population.

Base Sequence↗