Spinal muscular atrophy type II

A Chemical Biology Perspective to Therapeutic Regulation of RNA Splicing in Spinal Muscular Atrophy (SMA)

Manipulation of RNA splicing machinery has emerged as a drug modality. Here, we illustrate the potential of this novel paradigm to correct aberrant splicing events focused on the recent therapeutic advances in spinal muscular atrophy (SMA). SMA is an incurable neuromuscular disorder and at present the primary genetic cause of early infant death. This Review summarizes the exciting journey from the first reported SMA cases to the currently approved splicing-switching treatments, i.e., antisense oligonucleotides and small-molecule modifiers. We emphasize both chemical structures and molecular bases for recognition. We briefly discuss the advantages and disadvantages of these treatments and include the remaining challenges and future directions. Finally, we also predict that these success stories will contribute to further therapies for human diseases by RNA-splicing control.

Spinal Muscular Atrophy in the Black South African Population: A Matter of Rearrangement?

Spinal muscular atrophy (SMA) is a neuromuscular disorder, characterized by muscle atrophy and impaired mobility. A homozygous deletion of survival motor neuron 1 (SMN1), exon 7 is the main cause of SMA in ~94% of patients worldwide, but only accounts for 51% of South African (SA) black patients. SMN1 and its highly homologous centromeric copy, survival motor neuron 2 (SMN2), are located in a complex duplicated region. Unusual copy number variations (CNVs) have been reported in black patients, suggesting the presence of complex pathogenic rearrangements. The aim of this study was to further investigate the genetic cause of SMA in the black SA population. Multiplex ligation-dependent probe amplification (MLPA) testing was performed on 197 unrelated black patients referred for SMA testing (75 with a homozygous deletion of SMN1, exon 7; 50 with a homozygous deletion of SMN2, exon 7; and 72 clinically suggestive patients with no homozygous deletions). Furthermore, 122 black negative controls were tested. For comparison, 68 white individuals (30 with a homozygous deletion of SMN1, exon 7; 8 with a homozygous deletion of SMN2, exon 7 and 30 negative controls) were tested. Multiple copies (>2) of SMN1, exon 7 were observed in 50.8% (62/122) of black negative controls which could mask heterozygous SMN1 deletions and potential pathogenic CNVs. MLPA is not a reliable technique for detecting carriers in the black SA population. Large deletions extending into the rest of SMN1 and neighboring genes were more frequently observed in black patients with homozygous SMN1, exon 7 deletions when compared to white patients. Homozygous SMN2, exon 7 deletions were commonly observed in black individuals. No clear pathogenic CNVs were identified in black patients but discordant copy numbers of exons suggest complex rearrangements, which may potentially interrupt the SMN1 gene. Only 8.3% (6/72) of clinically suggestive patients had heterozygous deletions of SMN1, exon 7 (1:0) which is lower than previous SA reports of 69.5%. This study emphasizes the lack of understanding of the architecture of the SMN region as well as the cause of SMA in the black SA population. These factors need to be taken into account when counseling and performing diagnostic testing in black populations.

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.

A hungarian study on Werdnig-Hoffmann disease

The prevalence of Werdnig-Hoffmann disease was found to be 0.66 per 10,000 livebirths in Hungary from 1973 to 1980. However, the true prevalence is estimated to be 1 per 10,000 livebirths, which exceeds the level of a previously published English study. There was no higher fetal death rate in previous and subsequent pregnancies of index patients' mothers. The occurrence in sibs was 32%, probably because of greater ascertainment in families with more than one affected child.

Unusual pedigree patterns in seven families with spinal muscular atrophy; further evidence for the allelic model hypothesis

Clinical and genetic findings are presented in 18 patients, from 7 pedigrees with different types of spinal muscular atrophy (SMA). The SMA diagnosis was based on EMG and muscle biopsy findings. All 7 pedigrees show an unusual genetic pattern, not consistent with simple autosomal recessive inheritance. Furthermore, in 6 of the 7 pedigrees different types of SMA were present within each pedigree. Our findings can be explained by an extension of a multiple alleles hypothesis originally described by Becker in 1964.

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.

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.

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.

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.

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

A genetic study of the subacute spinal muscular atrophies (SMA) of late infancy and early childhood has been undertaken. All such patients with chronic disease (with ages at onset up to 14 years, and excluding SMA Type I) known to 2 large Neurological Centres were reassessed clinically and genetically. There were 124 index patients (67 females and 57 males) and 17 secondary cases, which formed two consecutive unselected series. To investigate the genetic composition of this group, 4 nosological approaches were used; cluster analysis of clinical features of the disease, Haldane's sib-sib analysis on familial cases, interpretation of frequency distribution histograms, and a segregation analysis. A single autosomal recessive gene accounts for over 90% of cases, causes a clinical syndrome which manifests its first clinical signs before 5 years of age and in almost all cases before two years of age, but which is compatible with life into the third decade. Moderate intrafamilial discordance for some clinical features may be observed, but no genetic heterogeneity within this group was demonstrated. A small group of cases is caused by (a) new dominant mutation(s), or (b) is composed of phenocopies, or both. This relatively uncommon form may comprise the majority of late-presenting cases, and may account for all cases which manifest the first signs after 5 years of age. The spectrum of age-at-onset of this group cannot be determined at present, but the disease may be manifest before the age of two years; it is clinically indistinguishable from SMA caused by an autosomal recessive gene. The literature has been reviewed in the light of these findings. Empirical risks for use in genetic counselling are presented.

High incidence of spinal muscular atrophy type I (Werdnig - Hoffmann disease) in the Karaite community in Israel

Spinal muscular atrophy (S.M.A.) type I (Infantile werdnig - Hoffmann Disease) was found in 4:1,600 (1:400) infants of the Egyptian Karaite community. This group constitutes a representative sample of the Egyptian Karaite community in Israel, which numbers at present somewhat more than 7,000. The community existed as a religious and reproductive isolate for over 10 centuries. The very high gene frequency, 0.05 for the autosomal recessive gene of S.M.A. type I, is probably the result of genetic drift.

[Werdnig-Hoffmann disease: report of two cases?]

Two cases of familial spinal muscular atrophy with onset in infancy are reported. The author makes an attempt to categorize them and concludes by Werdnig-Hoffmann disease.

Genetic investigations on chronic forms of infantile and juvenile spinal muscular atrophy

A material of 247 cases selected from 260 cases of spinal muscular atrophy in the Warsaw Department of Neurology in 1960-1974 was analyzed. The size of sibships was established and calculations were made of the mean distribution of the age at onset, also according to sex, for the different clinical forms, genetical proportions by the method of siblings and of probands, and coefficient of sib-sib correlation for the material as a whole and separately for males, females and male-female pairs. The analysis shows the course of the disease to differ between the sexes and to be mild in males more often than in females, as is particularly noticeable in the higher age groups. Cases of Kugelberg-Welander's disease are predominantly male. The hypothesis is advanced that a proportion of male patients have a sex-linked modifying gene of a fairly high frequency (possibly of the range of 1 in 5 males, and 1 in 25, in the homozygous state, in females). Although it would not disprove conclusively the nosological distinctness of different forms of infantile and juvenile spinal muscular atrophy, the existence of the modifying gene, if proved, would tend rather to add to the likelihood of their constituting a single recessive autosomal disease.

The nosology of the spinal muscular atrophies

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