Phenotype genotype analysis in 15 patients presenting a congenital myasthenic syndrome due to mutations in DOK7.

Congenital myasthenic syndromes (CMSs) are a heterogeneous group of diseases caused by genetic defects affecting neuromuscular transmission. Mutations of DOK7 have recently been described in recessive forms of CMS. Dok-7 is a cytoplasmic post-synaptic protein co-activator of the muscle-specific receptor-tyrosine kinase (MuSK) involved in neuromuscular synaptogenesis and maintenance. We report clinical, morphological and molecular data on 15 patients with mutations in DOK7. Eleven different mutations (5 novel) were identified and all patients but one were found to carry at least the common c.1124_1127dupTGCC mutation. Patients with DOK7 mutations have a particular limb-girdle pattern, without tubular aggregates but a frequent lipidosis on the muscle biopsy. Changes in pre- and post-synaptic compartments of the neuromuscular junction were also observed in muscle biopsies: terminal axons showed defective branching which resulted in a unique terminal axon contacting en passant postsynaptic cups. Clinical features, muscle biopsy findings or response to therapy were confusing in several patients. Characterization of this distinct phenotype is essential to provide clues for targeted genetic screening and to predict the therapeutic response to anticholinesterase treatments or ephedrine as has been suggested.

The CHRNE 1293insG founder mutation is a frequent cause of congenital myasthenia in North Africa.

OBJECTIVE: Mutations in various genes of the neuromuscular junction cause congenital myasthenic syndrome (CMS). A single truncating mutation (epsilon1293insG) in the acetylcholine receptor epsilon subunit gene (CHRNE) was most often identified in CMS families originating from North Africa and was possibly a founder mutation. METHODS: Twenty-three families were studied with an early onset form of CMS and originating from Tunisia, Algeria, Morocco, and Libya. Screening for the mutation epsilon1293insG was performed by direct sequencing. Haplotype analysis was done with 9 (CA)n repeat microsatellite markers and 6 SNPs flanking epsilon1293insG on chromosome 17p13-p12. Dating was calculated using the ESTIAGE method for rare genetic diseases. RESULTS: The epsilon1293insG mutation was identified in 14 families (about 60% of the initial 23). The expression of the CMS in affected members of these families was relatively homogeneous, without fetal involvement or being life-threatening, with moderate hypotonia and oculobulbar involvement, mild and stable disease course, and good response to cholinesterase inhibitors. Haplotype analysis revealed a common conserved haplotype encompassing a distance of 63 kb. The estimated age of the founder event was at least 700 years. CONCLUSIONS: These results strongly support the hypothesis that epsilon1293insG derives from an ancient single founder event in the North African population. Identification of founder mutations in isolated or inbred populations may have important implications in the context of molecular diagnosis and genetic counseling of patients and families by detection of heterozygous carriers.

Tubular aggregates are from whole sarcoplasmic reticulum origin: alterations in calcium binding protein expression in mouse skeletal muscle during aging.

Tubular aggregates are observed in various muscle disorders and appear as densely packed tubules believed to arise from sarcoplasmic reticulum of striated muscle. They are found both in human skeletal muscle, especially from patients suffering from 'tubular aggregate myopathy' and in fast twitch skeletal muscle of the male inbred mouse during aging. In this work, we studied tubular aggregates present in inbred male mouse skeletal muscle using electron microscopy as well as histochemistry and Western blotting with the main markers of the sarcoplasmic reticulum. We show that mouse tubular aggregates include the proteins SERCA 1, sarcalumenin (longitudinal sarcoplasmic reticulum), calsequestrin (terminal cisternae) and RyR1 (junctional sarcoplasmic reticulum). We demonstrate also that 95 and 51 kDa triadin isoforms are present in mouse skeletal muscle and are both components of tubular aggregates. These results support the hypothesis that tubular aggregates form a tubular arrangement of a complete sarcoplasmic reticulum containing the junctional, cisternae and longitudinal components of sarcoplasmic reticulum implicated in calcium homeostasis. During mouse skeletal muscle aging, however, densitometry of Western blots reveals a persistent decrease in the expression of the calcium binding protein calreticulin as well as a continuous increase in calsequestrin-like protein expression which both appear unrelated to the tubular aggregate formation.

Assessing gene and cell therapies applied in striated skeletal and cardiac muscle: is there a role for nuclear magnetic resonance?

Gene and cell therapies convey high hopes for treatment of skeletal and heart muscle diseases. In the experimental protocols under development as well as in the first clinical trials, longitudinal control by an atraumatic procedure is needed. Nuclear magnetic resonance (NMR), via its two modalities, imaging or spectroscopy, should play a major role both for in vivo animal and human studies, because of the great number of parameters that can be measured, sequentially or simultaneously, and because of its aptitude to monitor several steps of protocols, in particular to detect physiological modifications induced by therapies. We review here the many possible applications of nuclear magnetic resonance in gene/cell therapies where muscle is the target organ, with emphasis on the application of nuclear magnetic resonance to functional studies.

Electrotransfer of naked DNA in the skeletal muscles of animal models of muscular dystrophies.

The electrotransfer of naked DNA has recently been adapted to the transduction of skeletal muscle fibers. We investigated the short- and long-term efficacy of this methodology in wild-type animals and in mouse models of congenital muscular dystrophy (dy/dy, dy(2J)/dy(2J)), or Duchenne muscular dystrophy (mdx/mdx). Using a reporter construct, the short-term efficacy of fiber transduction reached 40% and was similar in wild-type, dy/dy and dy(2J)/dy(2J) animals, indicating that ongoing muscle fibrosis was not a major obstacle to the electrotransfer-mediated gene transfer. Although the complete rejection of transduced fibers was observed within 3 weeks in the absence of immunosuppression, the persistency was prolonged over 10 weeks when transient or continuous immunosuppressive regimens were used. Using therapeutic plasmids, we demonstrated that electrotransfer also allowed the transduction of large constructs encoding the laminin alpha2 chain in dy/dy mouse, or a chimeric dystrophin-EGFP protein in mdx/mdx mouse. The correct sarcolemmal localization of these structural proteins demonstrated the functional relevance of their expression in vivo, with a diffusion domain estimated to be 300 to 500 microm. However, degeneration-regeneration events hampered the long-term stability of transduced fibers. Given its efficacy for naked DNA transfer in these models of muscular dystrophies, and despite some limitations, gene electrotransfer methodology should be further explored as a potential avenue for treatment of muscular dystrophies.

Inhibition of fatty acid beta-oxidation in rat brain cultured astrocytes exposed to the neurotoxin 3-nitropropionic acid.

We describe the effects of the neurotoxin 3-nitropropionic acid (3-NPA) on fatty acid oxidation in neonatal rat brain astrocytes in primary culture, using a sensitive assay for beta-oxidation which depends on the release of 3H2O from [9,10(n)-3H]palmitic acid. 3-NPA is a suicide inhibitor of succinate dehydrogenase, a constituent of both Krebs cycle and complex II of the mitochondrial respiratory chain. It is widely distributed in plants and fungi. Neurotoxicity of 3-NPA to humans and animals, leading to selective neuronal cell death, appears mediated by the reduced level of ATP induced by the toxin. We demonstrated that 3-NPA can also impair energy metabolism in astrocytes. Exposure of astroglial cells in culture to 3-NPA leads to inhibition of the release of 3H2O from [9,10(n)-3H]palmitic acid. Addition of 2 mM 3-NPA to the culture medium caused a rapid decrease in beta-oxidation activity, which reached a plateau after 90 min. This inhibition was concentration-dependent. Concentration as low as 0.05 mM for 5 h significantly decreased beta-oxidation activity (25% inhibition). Half-maximal inhibition was obtained after treatment with 0.5 mM 3-NPA, and 3 mM induced a maximal response (63% inhibition) 3-NPA is clearly a potent inhibitor of beta-oxidation activity. We also show that 3-NPA 3 mM inhibits partially complex II (succinate ubiquinone reductase) and aspartate aminotransferase by 60 and 49% after 4 h treatment respectively. It has been shown that fatty acid is the preferred substrate for energy production in cultured astrocytes from developing brain. As astrocytes may also provide substrates alternative for energy metabolism in neurons and oligodendrocytes, it is likely that the inhibition of beta-oxidation by 3-NPA may contribute significantly to the damage induced by this toxin in the central nervous system.

Adrenoleukodystrophy in France: an epidemiological study.

An epidemiological study was conducted in France to estimate the prevalence of adrenoleukodystrophy, a severe neurologic X-linked disorder affecting boys and young men. 129 cases were collected. Analysis of all cases born between 1956 and 1986 with available clinical history allowed the calculation of the lowest estimation of the prevalence: 1 in 100,000 male births.

Infantile familial cardiomyopathy due to mitochondrial complex I and IV associated deficiency.

Two brothers, aged 27 and 20 months, born from consanguineous healthy parents, presented with cardiomyopathy, lactic acidosis and carnitine abnormalities in serum and muscle, without clinical evidence of muscle involvement. The histochemical reaction for cytochrome c oxidase (COX) activity was negative in all muscle fibres, although the holoenzyme and subunits were present at a normal level, as shown by immunocytochemistry. The COX activity was, respectively, 5 and 25% of control values, in muscle biopsies. Partial deficiency of complex IV was confirmed in fresh isolated muscle mitochondria from patient 2 and was associated with a defect of complex I. Patient 1 died at age 3 yr 6 months. Partial improvement of cardiomyopathy in patient 2 was obtained under carnitine therapy, but seizures occurred and CT scan and magnetic resonance imaging (MRI) revealed thalamic hypodensity. Thus, the disorder appears to be progressive despite the clinical stabilization of the cardiomyopathy. This further demonstrates the complexity and clinical heterogeneity of combined respiratory chain complex deficiencies.

[Symptomatic heterozygotic adrenoleukodystrophy in adults. 10 cases]. / Les adrénoleucodystrophies hétérozygotes symptomatiques de l'adulte: 10 cas.

Adult adrenoleukodystrophy is a X-linked peroxisomal disease associated with the accumulation of very long chain fatty acids (VLCFA) in tissues and body fluids. The diagnosis is established on the demonstration of elevated VLCFA in blood and cultured skin fibroblasts. Women are affected in nearly 15% of cases and neurological symptoms and/or signs develop in 53% of them. Identifying these women is important because of genetic counseling and a possible therapeutic approach. Ten cases of symptomatic heterozygous adult adrenoleukodystrophy are reported. Mean age at the time of diagnosis was 44.6 +/- 9.3 years. All patients presented with spastic paraparesis with inconstant and mild sensory or bladder disturbances. Cognitive impairment was present in 1 case. Cerebrospinal fluid was normal. Adrenal function in response to tetracosactide injection was abnormal in 1/7 cases. Electromyography detected a peripheral neuropathy in 1 case. Somatosensory evoked responses were abnormal in all cases, visual and auditory evoked responses in respectively 3/6 cases and 3/4 cases. Brain MRI detected non specific abnormalities in 3/7 cases; spinal cord MRI was normal in 3/3 cases. The familial history was helpful for the diagnosis in 3/10 cases. Examination of pedigrees detected 5 hemizygous and 1 asymptomatic heterozygous cases. All the patients were enrolled in a dietary study which adret with low VLCFA is currently under evaluation.

Genetic biochemical and pathophysiological characterization of a familial mitochondrial encephalomyopathy (MERRF).

Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome is a neuromuscular disorder characterized by mitochondrial myopathy and progressive myoclonus epilepsy. A heteroplasmic A to G transition mutation in the mitochondrial encoded tRNA(Lys) gene at nucleotide pair 8344 has been suggested to be linked to the MERRF-syndrome. We have investigated biochemically and histochemically muscle biopsies and studied the mitochondrial genomes of hair, blood and muscle tissue of a family including three cases of MERRF-syndrome as well as unaffected relatives within the maternal lineage. Sequence analysis of the mtDNAs, performed after amplification by the polymerase chain reaction (PCR), confirmed the A to G transition mutation in the tRNA(Lys) gene at position 8344. The additional point mutation at nucleotide pair 750 in the 12 S rRNA gene, which was also found by Shoffner et al. (1990), however, was absent in all investigated tissues. Quantitative analysis of the percentage of mutated mtDNA by mispairing PCR (Seibel et al., 1990) revealed variable contents in different tissues and individuals, including unaffected family members. Mitochondrial protein synthesis in cultured fibroblasts from MERRF patients revealed diminished incorporation of 35S-methionine into lysine-containing peptides.

Deletions of mitochondrial DNA in Kearns-Sayre syndrome and ocular myopathies: genetic, biochemical and morphological studies.

Genetic, biochemical and morphological investigations were conducted on skeletal muscle mitochondria from 6 cases of ocular myopathy: 4 cases with Kearns-Sayre syndrome (KSS) and 2 with chronic progressive external ophthalmoplegia. All of these 6 cases showed mitochondrial DNA (mtDNA) deletions in addition to normal sized DNA in the quadriceps muscle. The deletions ranging from 3 to 8 kbp were also mapped between nucleotides 5500 and 16000 by Southern blot. The deleted genes encoded for some subunits of complexes I, IV, V and 5-10 tRNAS. The boundaries of the deletions have been sequenced in three patients. Five patients had mitochondrial respiratory chain deficiency in complex I as shown by the low oxygen consumption in isolated mitochondria using three NAD(+)-linked substrates. Mitochondria with an abnormal ultrastructure were also observed in 2 cases. A good relationship between the cytochrome c oxidase deficiency and the amount of deleted mtDNA was shown in our present investigations.

The fasting test in paediatrics: application to the diagnosis of pathological hypo- and hyperketotic states.

A 24-h fasting test was performed in 48 control children, in 9 hypoketotic patients with inherited defects of fatty acid oxidation and in 2 hyperketotic patients with inherited defects of ketolysis. The control group was then divided into three age groups on the basis of different adaptation to fasting. Concentrations of blood glucose, lactate, free fatty acids (FFA), 3-hydroxybutyrate, acetoacetate and carnitine were measured after 15 h, 20 h and 24 h of fasting. Significant negative correlations were found in the control group between plasma total ketone bodies (KB) and plasma glucose (P less than 0.001), plasma carnitine (P less than 0.005) and the amplitude of glycaemic response to glucagon at the end of the fast (P less than 0.01). FFA/KB ratio and the product of final fasting values of glucose and ketones were useful to differentiate between hypoketotic or hyperketotic patients and normal subjects. In children with a suspected or definite hyperketotic or hypoketotic disorder, a fasting test must only be performed in healthy patients, in good nutritional condition with non-diagnostic basal biochemical investigations. Carefully supervised fasting should be continued sufficiently to allow ketogenesis and ketolysis to become activated.

Spectroscopic MRI: a tool for the evaluation of systemic lipid storage disease.

Spectroscopic MR imaging allows to measure the lipid content of a region inside the human body. This technique has been applied to the case of a woman with a severe multisystemic triglyceride storage disease. Lipid contents of liver, pancreas, kidneys, left ventricle, skeletal muscles (calves, thighs, arms) were measured by using the Dixon spectroscopic imaging sequence. In some heterogeneous muscles, localized proton spectra were recorded. Results agreed with clinical findings (muscle weakness, normal renal and cardiac function, diabetes). These techniques could help to quantify the severity of the disease and to follow up its evolution under therapy.

Sudden infant death syndrome and inherited disorders of fatty acid beta-oxidation.

Evidence that inherited disorders of mitochondrial fatty acid beta-oxidation can cause sudden infant death syndrome (SIDS) comes from case reports, systematic autopsy studies, and family studies. Family studies are important when no pediatric autopsy has been done, which is still frequent. After reviewing the fatty acid beta-oxidation, and its pathophysiology, we present the results of our metabolic study on 189 siblings of SIDS victims, and on 84 'near-miss' infants. We have found evidence for a disorder of fat oxidation in 28 (15%) infants in the first group, and in 14 (17%) infants in the second group. Diagnosing and treating such disorders early in infancy may prevent some cases of SIDS to occur.

Immunocytological and histochemical correlation in Kearns-Sayre syndrome with mtDNA deletion and partial cytochrome c oxidase deficiency in skeletal muscle.

We report histochemical, immunocytochemical, biochemical and molecular studies of skeletal muscle from a 23-year-old man with Kearns-Sayre syndrome. Southern blot analysis revealed a 4.7 kb heteroplasmic deletion of the mitochondrial DNA mapping within genes coding for subunits of complexes I, IV and V of the respiratory chain and for tRNA. Cytochrome c oxidase activity was decreased by 30% in isolated muscle mitochondria, without alteration of the Km. Histochemical and immunocytochemical correlation studies for cytochrome c oxidase revealed a lack of activity in 34% of individual muscle fibers including all the typical ragged-red fibers and a low percentage of immunodeficient fibers.

[Peroxisomes and neurologic diseases]. / Peroxysomes et pathologie neurologique.

Peroxisomes are ubiquitous subcellular organelles varying in number, size and enzymatic content according to species, tissues or physiological states. Microperoxisomes are present in the central nervous system and in muscle. Peroxisomes participate in anabolic and catabolic processes, including ether-lipid synthesis, bêta-oxidation, bile acid synthesis, prostaglandin catabolism. Very long chain fatty acids are specific substrates of peroxisomal acyl-CoA oxidase. Peroxisomal disorders occur as two main groups: 1/ disorders with multiple deficiencies of peroxisomal functions: Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease, rhizomelic chondrodysplasia punctata; 2/ disorders with a single peroxisomal enzyme defect: X-linked adrenoleukodystrophy, acatalasemia, type 1 hyperoxaluria, pseudo-Zellweger syndrome. Present therapy is tentative with some limited success. It includes peroxisomal inductors and lipid-controlled diet. Prenatal diagnosis and heterozygote detection allow genetic counselling in some peroxisomal disorders.

Value of radionuclide assessment with thallium 201 scintigraphy in carnitine deficiency cardiomyopathy.

The case of a 30 month-old boy who presented with isolated severe dilated cardiomyopathy is reported. The diagnosis of systemic carnitine deficiency was confirmed by low serum and tissue carnitine levels. During oral L-carnitine therapy, dramatic improvement of the cardiac function was assessed by radionuclide methods. Myocardial thallium 201 uptake was closely correlated with cardiac function studied by angioscintigraphy. These methods are simple, easily reproducible, non-invasive and involve little radiation. In a case of cardiomyopathy, we suggest an immediate trial of oral carnitine treatment; the efficacy of the therapy can be confirmed by isotopic tests with thallium 201 scintigraphy.

[Apparently idiopathic primary myocardiopathies in children. The role of metabolic etiology]. / Myocardiopathies primitives, d'apparence idiopathique, chez l'enfant. Place des étiologies métaboliques.

Thirty-three children presenting with "primitive" cardiomyopathy observed from January 1984 to December 1985 underwent a protocol of investigations consisting of histo-enzymatic study of the deltoid muscle, metabolic studies (glucose, free fatty acids, lactate, pyruvate, 3-hydroxybutyrate, aceto-acetate, carnitine, amino-acids blood levels after a 15 hour-fast; urinary organic acids chromatography) and a study of the fatty acids oxidation in cultured fibroblasts. In all children cardiac involvement was predominant and had been the cause for hospitalization. Cardiomyopathies of the hypertrophic type have an early onset, most often are part of a complex picture of extra-cardiac involvement and frequently have a lethal evolution. On the contrary, hypokinetic dilated cardiomyopathies are most often isolated, have a later onset and a less severe course. In 2 cases, an early hypokinetic dilated cardiomyopathy evolved toward hypertrophy. Peripheral muscular involvement is very frequent (lipidosis, mitochondrial aggregates or specific aspects) (60% of cases) in dilated as well as hypertrophic types. A precise etiological diagnosis or a strong presumption was possible in 12 of 33 cases: 2 with hereditary deficiency of the fatty acids beta-oxidation, 1 carnitine systemic deficiency, 1 Friedreich ataxia, 1 central core disease, 1 coxsackie B1 myocarditis, 6 strong suspicions of respiratory chain deficiency.

Adult adrenoleukodystrophy: a sporadic case?

This is a report of a case of the adult cerebral form of X-linked ALD. The 27-year-old patient presented with psychiatric disturbances. NMR was performed and compared to CT scan to define cerebral demyelination. The level of hexacosanoate was found to be increased in the patient's serum. Biochemical analysis of the patient's mother's serum and cultured fibroblasts and of serum samples from 10 other members of the family who could have been carriers of this X-linked disease, produced negative results. Hence, it is most likely that this case has occurred sporadically. HLA determination revealed the DR2 antigen which is often associated with multiple sclerosis.