A genetic study of subacute and chronic spinal muscular atrophy in childhood. A nosological analysis of 124 index patients

Pulmonary manifestations of neuromuscular disease with special reference to Duchenne muscular dystrophy and spinal muscular atrophy

Deterioration of respiratory function in patients with neuromuscular disorders is primarily responsible for the high mortality associated with these diseases. A review of Duchenne muscular dystrophy and spinal muscular atrophy, the leading neuromuscular disorders affecting children, will be followed by a critical analysis of the various pathophysiological mechanisms underlying respiratory manifestations in these patients. Among such mechanisms, the role of muscular weakness in preservation of lung function, mucociliary clearance, gas exchange at rest and during exercise, and respiratory control during wakefulness and sleep will be examined in detail. In addition, the potential benefits of respiratory muscle training and of early diagnosis and clinical intervention will be delineated. This review underscores the importance of periodic assessment of pulmonary function during wakefulness and sleep in children affected by neuromuscular diseases as an essential component of multidisciplinary care aimed at improving long-term morbidity, survival, and quality of life.

Prenatal prediction of spinal muscular atrophy in Chinese

We used linkage analysis, non-isotope SSCP (single-strand conformation polymorphism) and PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) for prenatal diagnosis of spinal muscular atrophy (SMA). A total of 26 cases from 20 SMA families (16, type 1 and 4) were evaluated. 5 out of 26 fetuses were affected and, following genetic counselling, the parents decided to terminate the pregnancies. Aborted fetal tissues were examined and the diagnosis was confirmed in each case. The 21 unaffected cases were either normals (12 cases) or carriers (9 cases). These children have been followed for six months to two and a half years. No false-negative or false-positive results on prenatal testing were found. We conclude that prenatal diagnosis of SMA is reliable and accurate.

Molecular basis of phenotypic heterogeneity in siblings with spinal muscular atrophy

We report on a family with childhood-onset spinal muscular atrophy with intrafamilial phenotypic variation. Typical of a large majority of such patients, both the child with spinal muscular atrophy type I and the child with type II were missing both copies of the survival motor neuron telomeric gene (SMN(T)). The more severely affected child, however, showed genotypic evidence consistent with the de novo loss of DNA sequence in addition to that inherited by both affected children. These data suggest that the intrafamilial phenotypic variation in this family results from a new mutation event in the more severely affected child. Examples of intrafamilial phenotypic variability are quite rare, but some reports exist in the spinal muscular atrophy literature. We present evidence that one explanation for this phenomenon is the occurrence of de novo deletion events at the highly unstable disease locus.

Fatty acid oxidation abnormalities in childhood-onset spinal muscular atrophy: primary or secondary defect(s)?

The purpose of this study was to further identify and quantify the fatty acid oxidation abnormalities in spinal muscular atrophy, correlate these with disease severity, and identify specific underlying defect(s). Fifteen children with spinal muscular atrophy (3 type I, 8 type II, 4 type III) were studied. Serum carnitine total/free ratios demonstrated a tendency toward an increased esterified fraction ranging 35-58% of total carnitine (normal: 25-30% of total) in younger children with types I and II. The remaining type II and III patients, older than 23 months of age at sampling, had normal esterified carnitine levels. Urinary organic acid analysis demonstrated mild to moderate medium-chain dicarboxylic aciduria in type I patients and normal, mild, or moderate increases in short-chain and medium-chain organic acids in type II patients. In the type III group, the organic acids were normal except for one patient with mild medium-chain dicarboxylic aciduria. Muscle intramitochondrial beta-oxidation was measured in 5 children (2 type I, 2 type II, and 1 type III) and a significant reduction in the activities of short-chain L-3-hydroxyacyl-CoA dehydrogenase, long-chain L-3-hydroxyacyl-CoA dehydrogenase, acetoacetyl-CoA thiolase, and 3-ketoacyl-CoA thiolase were found; however, normal crotonase activity was documented. Most strikingly, there was a marked increase (3- to 5-fold) in the activity ratios of crotonase to L-3-hydroxyacyl-CoA dehydrogenase and thiolase activities with both short- and long-chain substrates. The combined abnormalities suggest a defect in a mitochondrial multifunctional enzyme complex, distinct from the trifunctional enzyme. These abnormalities may be either primary or secondary and may respond to dietary measures to reduce the dependence on fatty acid oxidation.

Autosomal recessive proximal spinal muscular atrophy in 101 sibs out of 48 families: clinical picture, influence of gender, and genetic implications

We analysed the clinical picture of 101 sibs (43 sib pairs, 5 triplets) with autosomal recessive proximal spinal muscular atrophy (SMA). Linkage data of 20 sibships, which were available for analysis, were in agreement with chromosome 5q linkage. The patients were classified according to the motor development into SMA I (never sat), SMA II (sitting without support), and SMA III (walking without aids). Three sibs with adult onset (> 30 years = SMA IV) were discussed as a separate entity. Age-of-onset of the 101 patients showed a wide spectrum (prenatal to 47 years). Among sib pairs with SMA I and SMA II the ages-of-onset appeared to be very similar except of one atypically discordant sib pair. With regard to SMA III, 3 out of 13 sibships (23%) showed a marked variation in age-of-onset ranging from 5-15 years within a family. Concerning acquired motor development (ability to sit and walk), 7 sibships (15%) belonged to different SMA types. Ages of death in 29 sib pairs in whom at least one sib had died before the age of 20 years were strikingly discordant. Neither the degree of disability nor the respiratory deficits are reliable predictors of life expectancy. Although a predominance of males can be observed, no significant effect of gender has been established in familial cases. The existence of multiple allelism seems to be the most suitable explanation for the high interfamilial variability considering the clinical concordance in most affected sib pairs.

Population data on acute infantile and chronic childhood spinal muscular atrophy in Warsaw

This study provides epidemiological data on acute infantile (ASMA) and chronic childhood spinal (CSMA) muscular atrophy in Warsaw for the period 1976-1985. All calculations are based on the assumption that ASMA and CSMA result from mutations at two different gene loci. The incidence of ASMA and CSMA was 1 in 19474 live births with a corresponding gene and carrier frequency of 714 x 10(-5) and 1 in 70, respectively. The prevalence of CSMA for the year 1985 was 1.26 x 10(-5). These figures are higher than in similar studies in other countries. This fact might be connected with the careful ascertainment in this study.

Genetic mapping of chronic childhood-onset spinal muscular atrophy to chromosome 5q11.2-13.3

SPINAL muscular atrophy (SMA) describes a group of heritable degenerative diseases that selectively affect the alpha-motor neuron. Childhood-onset SMAs rank second in frequency to cystic fibrosis among autosomal recessive disorders, and are the leading cause of heritable infant mortality. Predictions that genetic heterogeneity underlies the differences between types of SMA, together with the aggressive nature of the most-severe infantile form, make linkage analysis of SMA potentially complex. We have now analysed 13 clinically heterogeneous SMA families. We find that 'chronic' childhood-onset SMA (including intermediate SMA or SMA type II, and Kugelberg-Welander or SMA type III) is genetically homogeneous, mapping to chromosomal region 5q11.2-13.3.

Chronic childhood spinal muscular atrophies in Algeria. A genetic study

This paper describes a genetic study of the chronic spinal muscular atrophies of late infancy and early childhood in Algeria. There were 50 index patients occurring in 44 kindreds and fourteen secondary cases. Genetic and nosological studies indicated that 52% of the patients constitute a genetically homogeneous subgroup with an age of onset between 3 and 24 months and an autosomal recessive mode of transmission. They also indicated that a large subgroup of index patients (48%) had a late age of onset, between 3 and 14 years. Such a large number of late presenting cases has not been reported in previous series. The majority of these cases are probably due to an autosomal recessive gene. A small proportion may represent new dominant mutations or nongenetic phenocopies. A possible sex influence on disease manifestations is discussed. A trend toward later male onset has been noted, and the degree of disability is more marked in males at or after the age of 10. Finally, some empirical risks for use in genetic counselling are presented.

Chronic proximal spinal muscular atrophy of childhood and adolescence: problems of classification and genetic counselling

Results obtained from a study of 354 cases of chronic proximal spinal muscular atrophy of childhood and adolescence suggest that the condition is not as homogeneous as it was previously thought. A tentative classification based on our results is proposed. Estimates of genetic risks are provided, taking into account the sex and age at clinical onset. In our opinion these factors are more reliable than the data hitherto available because they are based on a considerably larger series.

Chronic proximal spinal muscular atrophy of childhood and adolescence: sex influence

Segregation analysis was performed on 354 cases of chronic proximal spinal muscular atrophy of childhood and adolescence (CPSMA) in the total series and in a number of subgroups formed according to the age at onset and sex. The analysis provided evidence of sex influence in the series studied, particularly in a subgroup of the milder form of the disease with onset between the 37th month and 18th year of life. In the latter subgroup, females were affected much less frequently. This was particularly striking after age at onset of 8 years, and only exceptionally were females affected after the age of 13 years. These facts point to incomplete penetrance of the gene.

Clinical study of proximal spinal muscular atrophy. Report on 89 cases

A report on 89 cases of proximal Spinal Muscular Atrophy with observations on the clinical features, criteria of classification and modes of inheritance. The various forms into which SMA is divided probably represent a single disease that may begin at any age and may vary in severity, due, as a rule, to an autosomal recessive gene.

Late-childhood-onset spinal muscular atrophy in three Melanesian families in Papua New guinea

Late-childhood-onset spinal muscular atrophy (SMA) with rapid progression from proximal to distal muscle groups and leading to severe incapacity or death in adolescence or early adult life, was studied in two Melanesian families in Papua New Guinea. Probable SMA with cardiomyopathy was observed in a 12-year-old boy in a related family. The pattern of inheritance in the study group did not conform to any of the conventional Mendelian modes and it was conjectured that the disease was expressed in heterozygote carriers of the SMA gene only when an allelomorphic activator gene was present.

Succinic semialdehyde dehydrogenase deficiency

A coupled assay using [14C]4-aminobutyric acid and a direct assay using [14C]succinic semialdehyde have been designed to assay te activity of succinic semialdehyde dehydrogenase in a patient with 4-hydroxybutyric aciduria and family members. In the coupled assay less than 3% of control succinic semialdehyde dehydrogenase activity was found in lysates of lymphocytes isolated from whole blood of the patient. In the direct assay there was no detectable activity of the enzyme in lysates of isolated lymphocytes or cultured lymphoblasts. Results indicated the parents to be heterozygous carriers carriers of the abnormal gene, consistent with an autosomal recessive inheritance.

Classification of spinal muscular atrophies

Clinical heterogeneity within the spinal muscular atrophies (SMA) has long been a source of confusion for questions of prognosis and genetic counselling. Comprehensive clinical and genetic analyses of 240 consecutive index cases from two English centres (The English SMA Study) have enabled some nosological questions to be resolved. The different SMA syndromes can be discriminated by (a) age at the first clinical signs of the disease, (b) pattern of muscle involvement, (c) age at death of other patients within an affected kindred, and (d) genetic evidence. Seven different SMA syndromes can be defined clinically and genetically; thirteen mutant genes are incriminated. Prevalence and incidence figures are presented. SMA type I (Werdnig-Hoffman disease) and chronic childhood SMA together comprise 74% of all SMA cases. The classification of the spinal muscular atrophies presented also provides the differential diagnosis for newly presenting cases.

Chronic form of childhood spinal muscular atrophy. Are the problems of its genetics really solved?

The authors discuss the differences between the two large series of chronic childhood spinal muscular atrophies (SMA)--their own comprising 273 cases, and that of Pearn et al. comprising 141 cases. The main difference concerns the predominance of males in the clinically milder later-onset group in the present series. The data of Pearn et al. (1978a, b) are quite different. The reason for the discrepancies is apparently a different selection of material. The present material is highly selective in favour of chronic cases, and Kugelberg-Welander cases are well-represented, whereas the percentage of Kugelberg-Welander cases in the material of Pearn et al. was very small. Differences in selection also appear to be responsible for discordance in observations regarding influence of sex on the course of the disease. The present data seem to support the view that most of the cases revealing chronic forms of SMA (both mild and severe) are not distinct genetically. However, the possible existence of a distinct subgroup in which sex influence is strongly expressed is not excluded.

Blood selenium in chronic spinal muscular atrophy

The spinal muscular atrophies (SMA) of childhood comprise the second most common fatal recessive disease after cystic fibrosis, yet the nature of the biochemical defect causing the anterior horn cell degeneration is totally unknown. Recent reports of a cluster of adult motor neurone disease cases from a high seleniferous area in South Dakota have prompted the study of blood selenium in children with SMA in Australia. Eight children with chronic SMA were tested, in addition to 9 obligate heterozygote carriers of the gene. Blood selenium levels of patients and carriers did not differ significantly from that observed in controls. The mammalian effects of selenium toxicity are discussed.

Segregation analysis of chronic childhood spinal muscular atrophy

A formal segregation analysis for the disease 'chronic childhood spinal muscular atrophy' is presented. This disease is also known as 'Kugelberg-Welander disease', 'arrested Werdnig-Hoffmann disease', and 'chronic proximal or generalised spinal muscular atrophy'. There were 124 index cases occurring in 115 families. Ascertainment of index patients was by incomplete multiple selection. Three types of segregation analysis were performed: Weinberg Proband, an improved Weinberg Proband with a variance corrected formula for differences both in family size and ascertainment probability and a backeting technique assuming the extremes of both single and of truncate selection. All three methods gave similar results. The improved Weinberg Proband method with corrections for differences in ascertainment and in family size gave a segregation ratio of 0.18 and a 95% confidence range of 0.11 to 0.25. The mid-point of the bracketing method assuming extremes of truncate and of single selection was 0.19. The segregation ratio of that group of children with clinical onset before 9 months of age was 0.21, which does not differ significantly from the 0.25 predicted on the basis of autosomal recessivity. Evidence is presented to indicate that 25% of index patients may be due to new dominant mutations, or phenocopies, or both, and that these occur particularly among sporadic cases with clinical onset over 2 years of age. Empirical risk figures for use in genetic counselling are presented, and the literature of the subject is reviewed.

Autosomal dominant spinal muscular atrophy: a clinical and genetic study

A clinical and genetic study of 6 kindreds (13 patients) with autosomal dominant spinal muscular atrophy is presented. Evidence is presented to indicate that two separate autosomal dominant genes are involved. One of these causes clinical disease with onset in early childhood (birth--8 years), which is relatively benign and in which proximal selectively of muscle involvement is not marked. A separate autosomal dominant gene causes a disease with onset in adult life (median age 37 years), showing marked initial proximal selectively; this disease may be more rapid in its clinical progression. Penetrance of both genes approaches 100%. Incidence figures are presented; less than 2% of all cases of childhood onset spinal muscular atrophy, but 30% of adult onset cases, are due to an autosomal dominant gene transmitted from an affected parent. Implications for prognosis, diagnosis and genetic counselling are discussed. A review of 11 kindreds of dominant spinal muscular atrophy in the literature is presented.

A study of environmental factors in relation to fatal infantile spinal muscular atrophy (SMA type I). An analysis of birth order and parental age effects, social class, seasonal influence, and clustering in time and place

Major studies of the childhood spinal muscular atrophies have suggested that environmentally-produced phenocopies might occur, and that environmental factors might be important in some clinical features of these diseases. A formal analysis of some possible intra-uterine and post-natal influences has been undertaken in 78 index cases (72 families) of acute infantile SMA (acute Werdnig-Hoffmann disease; SMA Type I). There is no evidence to suggest that social class, parental age, birth order, or season of birth influences this disease or that clustering in time and place occurs.

A clinical study of chronic childhood spinal muscular atrophy. A review of 141 cases

The case histories and clinical details of 141 children (67 males and 74 females) with chronic childhood spinal muscular atrophy (SMA) have been reviewed. Hundred of these children were alive at the time of the study. The cases comprise a consecutive unselected series of all with this disease who presented to two large English neurological centres over a 10-year tracing period. Chronic childhood SMA is defined here as a progressive disease of anterior horn cells with initial proximal selectivity, which does not of itself cause death before 18 months of age. Clinical signs are first manifest between birth and 8 years of age, but in 95% before 3 years. Cumulative frequency tables for motor skills are presented; 46% of children never walked, even with orthopaedic aids; 37.6% were able to walk unaided at some stage. No child was able to run after 12 years of age. Late-presenting sporadic cases retain motor skills longer than do familial cases. A sex influence on the clinical course of the disease has been demonstrated, males being more severely affected. Cumulative frequency curves for age-at-onset and age-at-presentation have been compiled. A sib of an affected index case, still clinically normal at 2 years of age, has passed 90 percent of his risk period; the use of such cumulative frequency curves for studies of carrier-frequency and incidence is discussed. The median age at death for this disease exceeds 10 years. The range encompassed by the clinical spectrum is discussed.