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PubMed2005

SMNDelta7, the major product of the centromeric survival motor neuron (SMN2) gene, extends survival in mice with spinal muscular atrophy and associates with full-length SMN.

Spinal muscular atrophy (SMA) is an autosomal recessive disorder in humans which results in the loss of motor neurons. It is caused by reduced levels of the survival motor neuron (SMN) protein as a result of loss or mutation of the SMN1 gene. SMN is encoded by two genes, SMN1 and SMN2, which essentially differ by a single nucleotide in exon 7. As a result, the majority of the transcript from SMN2 lacks exon 7 (SMNDelta7). SMNDelta7 may be toxic and detrimental in SMA, which, if true, could lead to adverse effects with drugs that stimulate expression of SMN2. To determine the role of SMNDelta7 in SMA, we created transgenic mice expressing SMNDelta7 and crossed them onto a severe SMA background. We found that the SMNDelta7 is not detrimental in that it extends survival of SMA mice from 5.2 to 13.3 days. Unlike mice with selective deletion of SMN exon 7 in muscle, these mice with a small amount of full-length SMN (FL-SMN) did not show a dystrophic phenotype. This indicates that low levels of FL-SMN as found in SMA patients and absence of FL-SMN in muscle tissue have different effects and raises the question of the importance of high SMN levels in muscle in the presentation of SMA. SMN and SMNDelta7 can associate with each other and we suggest that this association stabilizes SMNDelta7 protein turnover and ameliorates the SMA phenotype by increasing the amount of oligomeric SMN. The increased survival of the SMNDelta7 SMA mice we report will facilitate testing of therapies and indicates the importance of considering co-complexes of SMN and SMNDelta7 when analyzing SMN function.

Animals↗
PubMed1994

Genetic heterogeneity in spinal muscular atrophy: a linkage analysis-based assessment.

The spinal muscular atrophies (SMAs) are among the most common autosomal recessive disorders. The mapping of the gene responsible for SMA to chromosome 5 has allowed the assessment of genetic heterogeneity in kindreds with a putative diagnosis of SMA. We report linkage analysis of 71 Canadian SMA families (types 1, 2, and 3) using polymorphisms that both flank and are linked to SMA. Data demonstrating nonlinkage to 5q markers were initially obtained in five kindreds; reexamination of the clinical status of these families showed that one fulfilled all the SMA diagnostic criteria, two showed patterns for which a diagnosis of SMA was possible but not conclusive, and two showed patterns for which the diagnosis of SMA appeared unlikely. This results in a degree of genetic heterogeneity between 1.5% and 4.5%. The three kindreds for which SMA appeared either possible or likely were simplex (ie, contained only one affected individual), and therefore the possibility that they represented new mutations could not be discounted. Thus, the significant majority of classic SMA cases are caused by a mutation in the 5q13.1 locus. Low genetic heterogeneity has implications for both genetic counseling and the applicability of conventional and genetic therapies following cloning of the SMA gene.

Adult↗
PubMed2002

Mimic syndromes in sporadic cases of progressive spinal muscular atrophy.

Described are patients initially diagnosed with progressive spinal muscular atrophy (PSMA), in whom further evaluation established another diagnosis. The authors prospectively investigated incident and prevalent cases of PSMA. Seventeen of 89 patients, after initial registration, were later excluded because reassessment revealed a diagnosis other than PSMA. In 11 of the 17 patients with a revised diagnosis, a potential treatment was available: multifocal motor neuropathy (7), chronic inflammatory demyelinating polyneuropathy (2), inflammatory myopathy (1), and MG (1). Other misdiagnoses included myopathy, syringomyelia, ALS, idiopathic chronic axonal polyneuropathy, and idiopathic brachial plexus neuropathy. One patient with a possible herniated lumbar disk recovered spontaneously.

Adult↗
PubMed1994

Evidence of autosomal dominant mutations in childhood-onset proximal spinal muscular atrophy.

Autosomal recessive and dominant inheritance of proximal spinal muscular atrophy (SMA) are well documented. Several genetic studies found a significant deviation from the assumption of recessive inheritance in SMA, with affected children in one generation. The existence of new autosomal dominant mutations has been assumed as the most suitable explantation, which is supported by three observations of this study: (1) The segregation ratio calculated in 333 families showed a significant deviation from autosomal recessive inheritance in the milder forms of SMA (P = .09 +/- .06 for onset at 10-36 mo and .13 +/- .07 for onset at > 36 mo; and P = .09 +/- .07 for SMA IIIa and .12 +/- .07 for SMA IIIb). (2) Three families with affected subjects in two generations are reported, in whom the disease could have started as an autosomal dominant mutation. (3) Linkage studies with chromosome 5q markers showed that in 5 (5.4%) of 93 informative families the patient shared identical haplotypes with at least one healthy sib. Other mechanisms, such as the existence of phenocopies, pseudodominance, or a second autosomal recessive gene locus, cannot be excluded in single families. The postulation of spontaneous mutations, however, is a suitable explanation for all three observations. Estimated risk figures for genetic counseling are given.

Adolescent↗
PubMed1990

Acute infantile spinal muscular atrophy. Muscle apoptosis as a proposed pathogenetic mechanism.

Biopsy as well as autopsy studies of a child who died 8 weeks after birth from the acute infantile form of spinal muscular atrophy revealed classical morphological changes, including degeneration and loss of motoneurons in the spinal cord, loss of large myelinated fibres in anterior roots and neurogenic atrophy in muscle. New ultrastructural findings include massive muscle cell elimination by apoptosis with the formation of membrane-bound muscle cell fragments, apoptotic bodies. In addition, numerous immature muscle fibres were observed. The morphological findings raise the possibility that in a severely growth-retarded muscle, the process of muscle cell apoptosis removes the peripheral target of anterior horn cells resulting in secondary motoneuron death.

Acute Disease↗
PubMed1990

Surgical treatment of scoliosis in a spinal muscular atrophy population.

Seventy-eight patients were diagnosed with spinal muscular atrophy between 1969 and 1988. Scoliosis developed in 34 of these patients, an incidence of 60%. Thirty-one patients could be retrospectively reviewed by chart review or interview. The average follow-up was 11.5 years. Onset of scoliosis averaged 8.8 years. Twenty-two patients were treated nonsurgically and nine surgically. Patients had improved sitting balance and endurance after surgery. Complications of surgery included loss of correction in one patient, one pseudarthrosis, and one patient who required prolonged ventilatory support. The prolonged survival of patients with spinal muscular atrophy justifies aggressive orthopaedic management of scoliosis to prevent progression of deformity and improve sitting comfort.

Braces↗
PubMed1997

Spinal Muscular Atrophies: An Ongoing Diagnostic Dilemma?

Background: Spinal muscular atrophies (SMAs) are a group of autosomal recessive disorders of anterior horn cell degeneration. Three genes-survival motor neuron (SMN), neuronal apoptosis inhibitory protein (NAIP), and, more recently, p44 (subunit of basal transcription factor II)-have been considered as candidate genes. The region spanning these genes has a complex organization, which makes molecular analysis difficult. Methods and Results: Molecular genetic testing of deletions of exons 7 and 8 of the SMN(T) (telomeric copy) gene and exon 5 of the NAIP(T) (telomeric copy) gene was performed in 39 diagnosed SMA patients, 31 cases referred as possible SMA, and 24 cases of prenatal diagnosis of SMA. Linkage analysis using markers flanking the SMA region was also performed. In general, the findings of involvement of SMN and NAIP gene deletions in patients diagnosed with SMA are in agreement with those previously published. One possible SMA case was found to be homozygously deleted only for exon 7 of SMN(T) and one deleted only for exon 5 of the NAIP(T) gene. Conclusions: SMAs exemplify human inherited disorders in which application of a variety of different techniques and a search for mutations in multiple genes are involved. Deletion testing of candidate genes (SMN, NAIP) is a powerful approach in patients affected or suspected of being affected with SMA. It is proposed that the direct SMN gene deletion test can be offered as the only test for prenatal diagnosis of SMA in families in which the clinically affected sibling has also been shown to have the homozygous deletion.

Journal Article↗
PubMed2003

[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↗
PubMed1989

Animal models of amyotrophic lateral sclerosis and the spinal muscular atrophies.

The causes of human amyotrophic lateral sclerosis (ALS) and the spinal muscular atrophies (SMA) are, almost without exception, unknown. This ignorance has stimulated the search for animal models to obtain insight into the etiology, pathogenesis and biochemical mechanisms underlying the human disorders. None of the 38 animal models, described in this review, provides an exact animal copy of a specific human motor neuron disease. Most of the models reproduce certain structural or physiological aspects of their human counterparts. The various experimental models can be classified according to the pathogenetic mechanism involved and according to the structural changes observed. Models based on experimentally induced disease, include heavy metals and trace elements (lead intoxication in guinea pigs, rabbits, rats, cats and primates; mercury intoxication in rats; aluminium intoxication in rabbits; swayback in goat kids; calcium and magnesium deficient rabbits and primates and calcium deficient cynomolgus monkeys), toxins (IDPN, vincristine, vinblastine, podophyllotoxin, colchicine, maytansine, maytanprine, L-BMAA, lectins, adriamycin), nutritional factors (ascorbic acid deficient guinea pigs), virus infection (spongiform polioencephalomyelitis, attenuated poliovirus, lactate dehydrogenase-elevating virus), and immunological factors (immunization with motor neurons). Hereditary models comprise hereditary canine spinal muscular atrophy, hereditary neurogenic amyotrophy in the pointer dog, Stockard paralysis, Swedish Lapland dog paralysis, "wobbler" mouse, "shaker" calf, and hereditary spinal muscular atrophy in zebra foals, crossbred rabbits,

Amyotrophic Lateral Sclerosis↗
PubMed1991

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↗
PubMed1994

Spinal muscular atrophy in calves of the Red Danish dairy breed.

Pathological and genetic aspects of spinal muscular atrophy in Red Danish dairy cattle are described. A total of 312 calves suspected of having the condition was reported in the Danish Bovine Genetic Disease Programme, 162 of them were examined post mortem and spinal muscular atrophy was diagnosed in 82 of these. Seventy-five per cent of the affected calves had bronchopneumonia. The diagnosis of spinal muscular atrophy was based on histopathological examinations of the spinal cord and musculature. The lesions were primarily characterised by degeneration of the spinal cord motor neurons with neuronophagia and denervation muscular atrophy. The ages of the affected calves varied from those recumbent from birth to a 21-week-old calf. All the necropsied cases appeared in a clearly familial pattern and could be traced back to American Brown Swiss bulls.

Animals↗
PubMed1993

[Anatomoclinical correlations of spinal muscular atrophy in infancy].

Forty-three cases of infantile spinal muscular atrophy diagnosed in our department between 1977 to 1991 are presented. Following clinical-pathologic evaluation, 27 cases were included in type I, 7 in type II and 9 cases in type III. The most frequent pathologic finding was the presence of large groups of atrophic fibers and hypertrophy of isolated fibers in muscle biopsy. Enzyme study showed higher mean levels of CPK and aldolase in type I with respect to the other two. Likewise, a significant statistical difference was found in the age of onset of the different groups. Finally, the clinical classification of spinal muscular atrophies in infancy is discussed.

Biopsy↗
PubMed2006

Respiratory failure in infants due to spinal muscular atrophy with respiratory distress type 1.

BACKGROUND: Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is a rare autosomal recessive neuromuscular disease of unknown prevalence characterized by degeneration of anterior horn alpha-motoneurons and manifesting in the first 6months of life as life-threatening irreversible diaphragmatic paralysis associated with progressive symmetrical muscular weakness (distal lower limbs mainly involved), muscle atrophy, and peripheral sensory neuropathy. SETTING: Pediatric intensive care unit of tertiary care hospital. PATIENTS: We present two new cases of SMARD1 and report two new mutations in the gene IGHMBP2 which encodes immunoglobulin mu-binding protein 2 on chromosome 11q13. CONCLUSIONS: SMARD1 is a poor-prognosis disease that should be considered when acute respiratory insufficiency, of suspected neuromuscular or unclear cause, develops during the first 6months of life. Diaphragmatic paralysis, manifesting as dyspnea and paradoxical respiration, is the most prominent presenting sign and diaphragmatic motility should be investigated early by fluoroscopy or ultrasound. Electromyography and nerve conduction studies revealing peripheral motor and sensory neuropathy then suggest the diagnosis which should be confirmed by genetic analysis.

DNA-Binding Proteins↗
PubMedDate not supplied

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↗
PubMed1996

Spinal muscular atrophies: recent insights and impact on molecular diagnosis.

Spinal muscular atrophies (SMA) are a group of motor neuron diseases characterized by degeneration of anterior horn cells of the spinal cord and by muscular atrophy. Childhood-onset SMA is one of the most frequent autosomal recessive diseases and a leading cause of infant mortality. The underlying biochemical defect of SMA is unknown. Recently two genes have been isolated from the critical region at 5q13, the survival motor neuron (SMN) gene and the neuronal apoptosis inhibitor protein (NAIP) gene. Both genes are frequently deleted in SMA patients. NAIP is deleted in at least 45% of severely affected patients but less frequently in the milder forms. Homozygous deletions of exon 7 of SMN are found in approximately 95% of patients independently of clinical severity. A few point mutations and microdeletions in SMN have also been reported. This high frequency of deletions makes SMN analysis an important molecular diagnostic tool for childhood-onset SMA and greatly facilitates prenatal diagnosis. SMN analysis has also proven useful for the diagnosis of adult-onset SMA and variant forms. Although questions such as phenotype-genotype correlation must still be solved, the isolation of SMN and adjacent genes constitutes an important step towards the understanding of the molecular basis of the disease.

Chromosomes, Human, Pair 5↗
PubMed1996

Unusual molecular findings in autosomal recessive spinal muscular atrophy.

All three types of autosomal recessive spinal muscular atrophy map to chromosome 5q11.2-q13.3 and are associated with deletions or mutations of the SMN (survival motor neurone) gene. The availability of a test to distinguish between the SMN gene and its nearly identical centromeric copy cBCD541 allows molecular diagnosis. We have analysed patients from 24 Belgian and 34 Turkish families for the presence or absence of a deletion in the SMN gene. A homozygous deletion in the SMN gene was seen in 90% of unrelated SMA patients. A non-radioactive SSCP assay allows for a semiquantitative analysis of the copy number of the centromeric and SMN genes. Hence, direct carrier detection has become feasible under certain conditions. We observed a phenotypically normal male, father of an SMA type I patient, presenting with only a single copy of the SMN gene and lacking both copies of the cBCD541 gene. This illustrates that a reduction of the total number of SMN and cBCD541 genes to a single SMN copy is compatible with normal life. In another SMA type I family, there is evidence for a de novo deletion of the centromeric gene in a normal sib. This observation illustrates the susceptibility of the SMA locus to de novo deletions and rearrangements.

Carrier State↗
PubMed2004

Spinal muscular atrophy: survival pattern and functional status.

OBJECTIVE: Spinal muscular atrophy (SMA) is common. The prevalence of SMA in southern Chinese is 1 in 53,000. The clinical course is variable. The traditional classification of SMA includes age of onset, age of death, achievement of motor milestones, and ambulatory status as criteria. There was a lack of inclusion of the best lifetime functional status of any child with SMA. With the advances in medical care, the life expectancy and ambulatory status of patients with SMA have improved. The objective of this study was to assess the survival pattern, ambulatory status, and functional status of children with SMA. METHODS: Patients with SMA were recruited from the neuromuscular clinic of the Duchess of Kent Children's Hospital, which is a university-affiliated hospital, and the Families of SMA in Hong Kong. By September 2002, 102 SMA cases had been registered in the Duchess of Kent Children's Hospital neuromuscular clinic and Families of SMA registry, and 83 patients were analyzed. Among them, 39 were recruited for the administration of Functional Independence Measure for Children (WeeFIM), an assessment tool for functional status that has been previously validated by us for Chinese children. The diagnosis of SMA was made from clinical history, serum muscle enzyme, electromyography, muscle biopsy, and, recently, by molecular studies. In Hong Kong, molecular tests of the survivor motor neuron gene was available since 1995. A total of 36 in our cohort of 83 patients had the diagnosis confirmed with molecular analyses. We adopted the classification of SMA from previous studies in which the criteria were based on the International SMA consortium (1992) with modifications according to the 59th European Neuromuscular Center International Workshops. As only SMA patients with childhood onset were studied, we did not include any type IV patients in our study. Parents were interviewed and records were reviewed for demographic and clinical data, including age of onset, gender, family history, motor milestones, disease progression, loss of motor function, and involvement of respiratory or bulbar muscles. We define the age of disease onset as the age in which the first abnormalities were obvious from the medical records or from the descriptions of the parents about the first signs of weakness, eg, age of achievement of certain motor milestones or loss of functions. For the ambulatory status, we define "being ambulatory" as having the ability to walk for 100 meters, either with assistance such as calipers or walkers or without assistance. Actuarial survival curves were obtained by using the Kaplan-Meier method for calculating survival probabilities and probabilities of remaining ambulatory. The parents or the chief caregivers were interviewed for functional status using WeeFIM at the last registered date in September 2002. The WeeFIM consists of 3 domains: 1) self-care, 2) mobility, and 3) cognition. The self-care domain consists of 8 items, namely eating, grooming, bathing, dressing (upper body), dressing (lower body), toileting, and bladder and bowel management. The mobility domain consists of 5 items: transfer from chair or wheelchair, transfer to toilet, transfer to tub or shower, walking/wheelchair/crawling distance, and moving up and down stairs. The cognition domain assesses comprehension, expression, social interaction, problem solving, and memory. A scoring scale from 1 to 7 was used (1 = total assistance, 2 = maximal assistance, 3 = moderate assistance, 4 = minimal contact assistance, 5 = supervision, 6 = modified independence, and 7 = complete independence). The maximum total WeeFIM score is 126, and the maximum score for self-care, mobility, and cognition are 56, 35, and 35, respectively. RESULTS: For type I SMA (n = 22), the survival probabilities at 1, 2, 4, 10, and 20 years were 50%, 40%, 30%, 30%, and 30%, respectively. For type II SMA (n = 26), the survival probabilities at 1, 2, 4, 10, and 20 years were 100%, 100%, 100%, 92%, and 92%, respectively. Sixteen of the SMA I patients and 4 of the SMA II patients died of cardiorespiratory failure. The 5 surviving SMA I patients all were ventilator dependent. All SMA III patients were surviving at the time of study. The probability of remaining ambulatory at 2, 4, 10, and 20 years after onset was 100%, 100%, 81%, and 50% for type IIIa (age of onset <3 years) and 100%, 100%, 84%, and 68% for type IIIb (age of onset between 3 and 30 years), respectively. The interval between disease onset and inability to walk was 15.0 +/- 10.9 years (mean +/- standard deviation) and 21.2 +/- 11.7 years for patients with SMA IIIa and IIIb, respectively. Only 39 patients participated in the WeeFIM interview as 20 had already died at the time of study and 24 refused participation. No difference could be found in the age of onset, gender, or types of SMA between those who participated (n = 39) and those who did not (n = 24). The mean total WeeFIM quotients were 24% for SMA type 1, 57% for SMA type 11, 75% for SMA type IIIa, and 78% for SMA type IIIb. For the self-care domain, 100% SMA type I and 73% SMA type II patients required assistance, whereas 55% and 63% of SMA types IIIa and IIIb patients achieved functional independence. Bathing and dressing (upper and lower body) were items with which most SMA children required help or supervision. For the mobility domain, assistance was needed in >90% of SMA types I, II, and IIIa and in 63% of SMA type IIIb patients. Stair management was the major obstacle for independence in achieving mobility for all types of SMA. For the cognition domain, performance was the best among the 3 domains, and 60% of SMA type II, 78% of SMA type IIIa, and 90% of SMA type IIIb patients achieved functional independence. However, except for SMA type IIIb, a significant proportion of patients still need assistance or supervision in the area of problem solving. Statistically significant differences were found in the WeeFIM scores between type I and type II and between type IIIa and IIIb patients. However, no significant difference could be observed between type II and type IIIa SMA patients in the overall WeeFIM scores or performance in any of the 3 domains. CONCLUSION: We found that there was improvement in survival in SMA patients as compared with other studies. Assistance or supervision was needed for the majority of SMA patients for both mobility and self-care domains. With improvement in survival as a result of medical advances, assessment of the most current or the best-ever functional status at a designated age might be an important criterion for classification of SMA.

Activities of Daily Living↗