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Mutations of the LMNA gene can mimic autosomal dominant proximal spinal muscular atrophy.

The molecular basis of autosomal dominant spinal muscular atrophy (AD-SMA) is largely unknown. Because the phenotypic spectrum of diseases caused by LMNA mutations is extremely broad and includes myopathies, neuropathies, and cardiomyopathies designated as class 1 laminopathies, we sequenced the LMNA gene in index patients with the clinical picture of proximal SMA, who had a family history suggestive of autosomal dominant inheritance. Among the 19 families investigated, two showed pathogenic mutations of the LMNA gene, resulting in the diagnosis of a class 1 laminopathy in about 10% of our series. We found one novel truncating mutation (c.1477C > T, Q493X) and one previously described missense mutation (c.1130G > T, R377H) in the LMNA gene of two unrelated patients with adult-onset proximal SMA followed by cardiac involvement 14 and 22 years after the onset of weakness. The pedigrees of both families revealed a high frequency of cardiac abnormalities or sudden deaths. Our findings extend the spectrum of laminopathies and are of relevance for genetic counseling and clinical care of families presenting with adult-onset proximal SMA. Particularly, if neurogenic atrophy is combined with a cardiac disease in a family, this should prompt LMNA mutation analysis.

Adult↗

[Neuromuscular diseases (NME). I. Spinal muscular atrophy, peripheral nerve diseases, congenital myasthenia gravis].

Among the group of clinically and genetically heterogeneous spinal muscular atrophies(SMA), the autosomal recessive proximal types I-III are the most frequent. They are caused by mutations of the telomeric copy of the survival motor neuron gene (SMN1) on chromosome sq while loss of the centromeric copy (SMN2) does not lead to SMA. The conservation of exon 7 in the SMN2 copy seems to be crucial for possible causal therapy options. The genetic defect is also known for spinal muscular atrophy with respiratory distress. Hereditary polyneuropathies are caused by mutations in several genes on different chromosomes. Genetic and phenotypic heterogeneity must be considered. Data on clinical symptoms, inheritance, and neurophysiology are obligatory for the most effective molecular analysis. Hereditary congenital myasthenic syndromes are clinically, genetically, and pathogenetically heterogeneous. The diagnostic significance of molecular genetic analyses is still increasing. Therapeutic options include oral medication and assisted ventilation as needed.

Humans↗

Long-term observations of patients with infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1).

We describe 6 unrelated patients affected by infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1) with prolonged survival upon mechanical ventilation (4.5-11 years), which has not been reported before. Biallelic mutations in the IGHMBP2 gene proved the diagnosis of SMARD1 in all patients. Disease onset was in the first 2 months in the described patients, starting with generalised hypotonia, failure to thrive, and early breathing difficulties. Diaphragmatic palsy was diagnosed and permanent ventilation was initiated 2-8 months after onset. Within months a more distal muscular atrophy became evident associated with joint contractures (talipes), hand drops, and fatty finger pads. Motor development remained minimal, loss of function was observed within the first year after which no further progression was recorded. Voiding dysfunction with reflux nephropathy was observed in 3 patients and has not been reported before. Further evidence of autonomic nerve dysfunction resulting in cardiac arrhythmia, hypertension, and excessive sweating was given in 2 patients. Investigative results were largely compatible with those obtained in classic SMA. However, neurogenic atrophy muscle was more pronounced in distal muscles, if examined, and there was evidence of peripheral nerve involvement at least in some patients.

Age Factors↗

A predominantly cervical form of spinal muscular atrophy.

Clinical heterogeneity within the group of spinal muscular atrophies (SMA) in children can pose practical problems of diagnosis, prognosis and genetic counselling. In addition to the classic forms, unusual cases have been described. Five children with an atypical type of SMA are reported, characterised by early involvement of cervical muscles contrasting with initially mild or absent affection of peripheral muscles. Secondary involvement of respiratory muscles was responsible for the death of three children in the second to fourth year. The disorder may be recessively inherited.

Female↗

An autopsy case of peroneal muscular atrophy with rigidity and tremor. Ultrastructural and systematic morphometrical studies on peripheral nerves.

An autopsy case of hereditary peroneal muscular atrophy (PMA) with rigidity and static tremor is presented. The patient developed slowly progressive distal muscular atrophy of the legs at the age of 15 years. By the age of 52 years, PMA became marked associated with pes cavus, and tremor and rigidity of the extremities were noted. Motor and sensory conduction velocities gradually depressed and lost near the end of his life. At autopsy, the major neuropathological abnormalities involved the peripheral nervous systems, and were characterized by axonal atrophy and loss of myelinated fibers. These changes involved both the proximal and distal nerves, being more severely affected in the distal. The pathological changes in other regions of the nervous systems were mainly confined to the spinal cord, dorsal ganglia and spinal nerve roots, and pigmented neurons in the brain stem. Morphometrically, the total fascicular area was much smaller than in control, but the total number of myelinated fibers greatly outnumbered that of control 75,200 to 48,200 at the proximal sciatic nerve and then gradually decreased towards the periphery; however, even in the distal sural nerve, the total number of myelinated fibers exceeded that of control (6820 to 5469). Thus, the density of myelinated fibers were much higher, being 1.5 to 2 times greater, than in control. Its abrupt decline at the distal nerve might account for neurogenic atrophy of the distal musculature. Unmyelinated fibers were slightly increased in density and not atrophic. This case is unique in its clinicopathology and does not belong to any subtypes of PMA including "neuronal plus".

Adult↗

[Proximal autosomal recessive types of spinal muscular atrophy].

One hundred and three patients with spinal muscular atrophy (SMA) were registered in a population medical genetic study of autosomal recessive childhood proximal SMA in Saratov region. Twenty-five patients were investigated complexly, using biochemical analysis of some enzymes, electroneuromyography, magnetic resonance imaging of spinal cord, muscle biopsy and molecular genetic testing. Pronounced clinical polymorphism and genetic heterogeneity of the disease were revealed.

Biopsy↗

Peroneal muscular atrophy with parkinsonism, ptosis, and congenital strabismus.

Peroneal muscular atrophy (PMA) may be occasionally associated with other neurodegenerative features including parkinsonism. We report the association of PMA of neuronal type with parkinsonism, ptosis and congenital strabismus in a 62-year-old Sicilian woman. The complete syndrome was present only in the proband, but variously combined features were present in ten other family members over four generations, with likely autosomal dominant inheritance. Although a similar syndrome of PMA, ptosis, parkinsonism and dementia was already reported, this family showed a previously undescribed combination of features in view of the presence of congenital strabismus.

Blepharoptosis↗

Spinal surgery in spinal muscular atrophy.

Fifteen patients with surgical treatment of spinal muscular atrophy were reviewed. The curve pattern was thoracic in 3, thoracolumbar in 11, and double thoracic and thoracolumbar in 1. Follow-up averaged 31 months. Eleven patients underwent posterior spinal fusion with Harrington instrumentation, with segmental wiring in four, and two had Luque instrumentation. The average age at time of surgery was 14.4 years. The average curve correction was 48%; that with the pelvic obliquity corrected, 63%. Surgery is best done when the curve is approximately 50-60 degrees, and Luque sublaminar wiring of Harrington or Luque rods with no external support appears to be the procedure of choice.

Adolescent↗

[Pseudodominant inheritance of spinal muscular atrophy--father and son suffering from SMA].

Spinal muscular atrophy (SMA) is an autosomal recessive hereditary disorder caused by mutations of the SMN1 gene. Because of the autosomal recessive type of transmission, the genetic risk of the disease in the following generations is small and is estimated to be about 1%. Here we present a case report of a father and son suffering from SMA. The father is affected with a mild form of SMA, with onset at about 13 years of age. The son suffers from SMA type 2, with onset at about 13 months of age. In both father and son, genetic analysis showed biallelic deletion of exons 7 and 8 in the SMN1 gene. The boy's mother is a carrier of the deletion at the SMA locus. Quantitative analysis revealed one copy of the SMN1 gene.

Adult↗

Testosterone therapy and the pathogenesis of Kennedy's disease (X-linked bulbospinal muscular atrophy).

The mutation in X-linked bulbospinal muscular atrophy (XBSMA) is an increased CAG triplet repeat coding for a polyglutamine domain in the gene for the androgen receptor. This might impair the effect of testosterone on motor neurons, leading to their progressive degeneration. We report a trial of high-dose oral testosterone therapy in two brothers with XBSMA. Patient 1 received 37.5 mg of testosterone daily for more than 18 months, and Patient 2 received 25 mg per day for six months, both in combination with exercise therapy. Patient 1 showed improvement of up to 300% in muscle work output. Patient 2, who did less exercise, had no symptomatic improvement. These results indicate that exogenous testosterone therapy is not harmful, and may produce functional improvement when combined with exercise. We hypothesize that high-dose testosterone may reduce a toxic gain of function that the mutation produces, perhaps by inhibiting glutamate neurotoxicity.

Aged↗

Riluzole attenuates spinal muscular atrophy disease progression in a mouse model.

Spinal muscular atrophy (SMA) is a motor neuron disease caused by mutations of the survival motor neuron 1 gene (SMN1). No curative treatment is available. Mutant mice carrying homozygous deletion of Smn exon 7 directed to neurons display a degenerative process of motor neurons similar to that found in human SMA. To test whether riluzole, which exhibits neurotrophic properties, might have a protective role in SMA, mutant mice were treated with it after the onset of the degenerative process. Riluzole improved median survival and exerted a protective effect against aberrant cytoskeletal organization of motor synaptic terminals but not against loss of proximal axons. These results demonstrate that the disease course of SMA can be attenuated after the onset of neuromuscular defects and may warrant further investigation in a therapeutic trial in SMA.

Animals↗

Canine storage disease characterized by hereditary progressive neurogenic muscular atrophy: breeding experiments and clinical manifestation.

Progressive neurogenic muscular atrophy due to storage of a compound lipid in the lower motor neurons was diagnosed in 3 English Pointers that were littermates. Using 2 clinically normal littermates of these 3 affected dogs and 2 clinically normal dogs of the 2nd litter from the parents of the original 3 affected dogs as the initial breeding stock, a breeding experiment was performed, resulting in a breeding line of 26 dogs, 4 of which had the disease and 6 of which died before 3 months of age. Results indicated that the disease may have an autosomal recessive mode of inheritance. The clinical manifestation and electrophysiologic findings indicated lower motor neuron involvement in the affected dogs produced by breeding consistent with findings in the original 3 affected dogs. Upper motor neurons or the sensory system was not involved. The disease appeared to be distinct from other canine storage diseases previously reported.

Animals↗

SMN protein analysis in fibroblast, amniocyte and CVS cultures from spinal muscular atrophy patients and its relevance for diagnosis.

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by the homozygous absence of the telomeric copy of the survival motor neuron (SMNt) gene, due to deletion, gene conversion or point mutation. SMNt and its homologous centromeric copy (SMNc) encode the SMN protein, which is diffusely present in the cytoplasm and in dot-like structures, called gems, in the nucleus. We have studied the SMN protein in different cell cultures, including fibroblasts, amniocytes and CVS cells from SMA individuals and controls. By immunofluorescence analysis we found a marked reduction in the number of gems in fibroblasts, amniocytes and chorionic villus cells of all SMA patients and foetuses, independent of the type of the genetic defect. We also show that immunolocalisation of the SMN protein may be a useful tool for the characterisation of particular patients of uncertain molecular diagnosis.

Amniotic Fluid↗

Spinal muscular atrophy: kinematic breathing analysis.

Twelve children with spinal muscular atrophy (SMA) type 2 and 13 children without physical disability underwent kinematic analysis of thoracoabdominal volume changes when breathing spontaneously and when breathing deeply. A very accurate optical method of kinematic analysis was used. Volumes were partitioned into upper thoracic, lower thoracic, and abdominal compartments. Abdominal volume increases accounted for 96% of the normal tidal volumes and 87% of the deep breathing volumes for the patients, but only 74 and 41% of the volumes, respectively, for the controls. For the patients the upper thoracic contribution to breathing volumes was --1.7% for normal tidal volumes and 0.3% for deep breathing volumes. Patients with less upper thoracic kinematic reserve were also found to be more likely to have chronic nocturnal hypoventilation. We conclude that kinematic analysis can be helpful in determining differences in regional lung mobility and risk for nocturnal ventilatory dysfunction for children with SMA. Therapeutic interventions need to be addressed to maintain thoracic kinematic reserve and lung compliance and, thereby, to facilitate more normal lung growth and the ability to cough.

Adolescent↗

Myosin heavy chain composition of muscle fibers in spinal muscular atrophy.

Muscle biopsies from 20 cases of spinal muscular atrophy (SMA), mostly diagnosed as Werdnig-Hoffmann (W-H) disease, were examined for myosin heavy chain (HC) composition. The fetal, fast, and slow heavy chains were characterized in the isolated muscle myosin, and in myosin of single, chemically skinned fibers, by electrophoresis in SDS-6% polyacrylamide gels and by immunoblot techniques, using specific antibodies directed to each main type of myosin HC. The fiber distribution of myosin HC isozymes was further investigated on muscle cryostat sections by an indirect immunofluorescent technique. Fetal myosin HC was found to be expressed in a subpopulation of severely atrophic fibers, alone or together with the slow form of myosin HC. Triangulated fibers of intermediate size contained fetal and fast myosin or fast myosin alone. The hypertrophic fibers were characterized by the predominant expression of slow myosin HC; but in some of these fibers, also low amounts of HC fetal were found to be expressed. These findings are discussed in relation to developmental transitions of myosin heavy chains in human muscle.

Child, Preschool↗

Sequence of a 131-kb region of 5q13.1 containing the spinal muscular atrophy candidate genes SMN and NAIP.

The spinal muscular atrophies (SMA), which are characterized by motor neuron loss and progressive paralysis, are among the most common autosomal recessive disorders. The SMA region of chromosome 5q13.1 is distinguished by variable amplification of genomic sequence incorporating a number of genes and pseudogenes. Recently, two SMA candidate genes mapping to this area were identified: survival motor neuron (SMN) and neuronal apoptosis inhibitory protein (NAIP). The telomeric copy of SMN (SMNtel) is deleted in over 95% of cases of SMA, with NAIP deletions primarily seen in type I SMA. We present here 131 kb of genomic sequence from 5q13.1 incorporating both NAIP and SMNtel in addition to revisions of the original NAIP cDNA sequence. The Alu-rich NAIP-SMNtel interval contains the microsatellite polymorphisms that are deleted in as many as 80% of type I SMA chromosomes, focusing attention on this region in the pathogenesis of type I SMA.

Amino Acid Sequence↗

Preimplantation genetic diagnosis for spinal and bulbar muscular atrophy (SBMA).

X-linked spinal and bulbar muscular atrophy is characterized by adult onset motor neuron disease and results from a defect in the androgen receptor. The disease is caused by a dynamic mutation in the first exon of the androgen receptor gene, involving a CAG trinucleotide repeat. We have developed a single-cell polymerase chain reaction assay for the androgen receptor gene and describe the application of this assay for preimlantation genetic diagnosis (PGD) in a couple at risk, where the female partner is a carrier of 47 repeats. Diagnosis was based on the detection of both normal and expanded alleles. Allele dropout of the expanded allele was observed in only 1 of 25 lymphoblasts of the carrier and of a non-expanded allele in 1 of 20 research blastomeres tested before the actual PGD. One contraction of four repeats was also found in the carrier's lymphoblasts. Neither expansions nor contractions were observed in the blastomeres biopsied from 11 embryos. Two embryos were unaffected, eight were female carriers and one was an affected male embryo.

Alleles↗

Prospective study of spinal muscular atrophy before age 6 years. DCN/SMA Group.

Spinal muscular atrophy (SMA) is a common neuromuscular disorder of childhood, associated with a high mortality rate during the first 2 years of life. Most practitioners expect patients with SMA to follow a progressive course with loss of muscle strength and function over 2-10 years. Counselling sessions with parents frequently emphasize the high mortality rate and risk for respiratory failure. The progressive nature of SMA has been attributed to the loss of motor neurons. Fifty-eight children, ages 6 years and younger, were examined between January, 1987, and April, 1992, as part of a large, multicenter collaborative study of SMA. Muscle function was evaluated at regular intervals using a standardized protocol that was demonstrated to be reliable. We determined a prevalence of 56% for tongue fasciculations, a prevalence of 22% for facial weakness, and persistent deep tendon reflexes in one patient. Improved motor function and acquired milestones during the study were documented. This work should contribute toward a better understanding of the natural history of SMA.

Child↗