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Biomedical subjects

B Wirth

Publications and source records attributed to B Wirth.

At least 19 recordsLinked to original sources
PubMed2006

Mildly affected patients with spinal muscular atrophy are partially protected by an increased SMN2 copy number.

Spinal muscular atrophy (SMA) is a recessive neuromuscular disorder caused by loss of the SMN1 gene. The clinical distinction between SMA type I to IV reflects different age of onset and disease severity. SMN2, a nearly identical copy gene of SMN1, produces only 10% of full-length SMN RNA/protein and is an excellent target for a potential therapy. Several clinical trials with drugs that increase the SMN2 expression such as valproic acid and phenylbutyrate are in progress. Solid natural history data for SMA are crucial to enable a correlation between genotype and phenotype as well as the outcome of therapy. We provide genotypic and phenotypic data from 115 SMA patients with type IIIa (age of onset <3 years), type IIIb (age of onset >3 years) and rare type IV (onset >30 years). While 62% of type IIIa patients carry two or three SMN2 copies, 65% of type IIIb patients carry four or five SMN2 copies. Three type IV SMA patients had four and one had six SMN2 copies. Our data support the disease-modifying role of SMN2 leading to later onset and a better prognosis. A statistically significant correlation for > or =4 SMN2 copies with SMA type IIIb or a milder phenotype suggests that SMN2 copy number can be used as a clinical prognostic indicator in SMA patients. The additional case of a foetus with homozygous SMN1 deletion and postnatal measurement of five SMN2 copies illustrates the role of genotypic information in making informed decisions on the management and therapy of such patients.

Adult↗
PubMed2005

Molecular and functional analysis of intragenic SMN1 mutations in patients with spinal muscular atrophy.

The autosomal recessive spinal muscular atrophy (SMA), a neuromuscular disease and frequent cause of early death in childhood, is caused in 96% of patients by homozygous absence of the survival motor neuron gene (SMN1). The severity of the disease is mainly determined by the copy number of SMN2, a copy gene which predominantly produces exon 7-skipped transcripts and only low amount of full-length transcripts that encode for a protein identical to SMN1. Only about 4% of SMA patients bear one SMN1 copy with an intragenic mutation. A comprehensive molecular genetic analysis of 34 SMA patients who carry one SMN1 gene is presented, including 18 that were previously published. Haplotype analysis with the microsatellite markers Ag1-CA and C212 in these SMA families turned out to be a reliable accessory method in predicting known SMN1 mutations in SMA patients carrying one SMN1 copy. Five novel missense mutations were identified that are localized in: exon 2a c.88G>A (p.D30N) and c.131A>T (p.D44V); exon 3 c.283G>C (p.G95R) and c.332C>G (p.A111G); and exon 6 c.784A>G (p.S262G), respectively. The survival motor neuron (SMN) protein has been shown to be a component of a large complex (termed the SMN complex) that promotes the formation of spliceosomal U small nuclear ribonucleoproteins (snRNPs). Within this complex, SMN forms oligomers and directly interacts via its N-terminus with SMN-interacting protein 1 (SIP1) and via its central Tudor domain with spliceosomal (Sm) proteins. We performed in vitro interaction studies to test whether SMA-causing missense mutations identified in this study interfere with the reported interactions of SMN. Our results show that mutations p.G95R and p.A111G reduce SMN binding to Sm proteins, further confirming the previous finding that the Tudor domain is the essential binding site of SMN to Sm-proteins. However, all mutations, including those in exon 2a, a region shown to be important for the binding of SMN to SIP1, do not disturb the interaction of SMN to SIP1.

Adolescent↗
PubMed2005

Limits of locomotor ability in subjects with a spinal cord injury.

STUDY DESIGN: Case-control study with pair-wise matching. OBJECTIVES: To investigate the level of locomotor performance in spinal cord injury (SCI) subjects. SETTING: Spinal Cord Injury Center of Balgrist University Hospital in Zurich, Switzerland. METHODS: Seven well-recovered SCI subjects and controls performed three tests: (1) 6-Min Walk Test (6MWT), (2) treadmill walking with full and restricted vision and (3) repetitive stepping over an obstacle. In the latter task, the subjects had to step over an obstacle as low as possible, without touching it. The subjects performed three blocks of 50 trials each. They received acoustic signals that indicated obstacle approach and foot clearance. During the third block, vision was restricted. The main outcome measures were: (1) distance walked, (2) leg muscle activity, joint kinematics and double-support duration, (3) foot clearance, number of obstacle hits, leg muscle activity, joint kinematics and swing phase duration. RESULTS: (1) No difference in the 6MWT between the groups. (2) Independent from vision, the double-support duration was increased in SCI subjects. (3) SCI subjects learned generally at a slower rate. They touched the obstacle more frequently when vision became restricted. Furthermore, we observed differences between the groups in rectus femoris and tibialis anterior EMG activity and swing phase duration. CONCLUSION: It appears that even in well-recovered SCI subjects, small deficiencies in functional gait can be determined, which remain undetected by clinical walking tests. In addition, SCI subjects learned a locomotor task at a slower rate. This indicates that rehabilitation programs should train (adaptive) locomotion in different (sensory) environments.

Adaptation, Physiological↗
PubMed2004

Differential evolution of the Saccharomyces cerevisiae DUP240 paralogs and implication of recombination in phylogeny.

Multigene families are observed in all genomes sequenced so far and are the reflection of key evolutionary mechanisms. The DUP240 family, identified in Saccharomyces cerevisiae strain S288C, is composed of 10 paralogs: seven are organized as two tandem repeats and three are solo ORFs. To investigate the evolution of the three solo paralogs, YAR023c, YCR007c and YHL044w, we performed a comparative analysis between 15 S.cerevisiae strains. These three ORFs are present in all strains and the conservation of synteny indicates that they are not frequently involved in chromosomal reshaping, in contrast to the DUP240 ORFs organized in tandem repeats. Our analysis of nucleotide and amino acid variations indicates that YAR023c and YHL044w fix mutations more easily than YCR007c, although they all belong to the same multigene family. This comparative analysis was also conducted with five arbitrarily chosen Ascomycetes-specific genes and five arbitrarily chosen common genes (genes that have a homolog in at least one non-Ascomycetes organism). Ascomycetes-specific genes appear to be diverging faster than common genes in the S.cerevisiae species, a situation that was previously described between different yeast species. Our results point to the strong contribution, during DNA sequence evolution, of allelic recombination besides nucleotide substitution.

Base Sequence↗
PubMed2003

Valproic acid increases the SMN2 protein level: a well-known drug as a potential therapy for spinal muscular atrophy.

Proximal spinal muscular atrophy (SMA) is a common neuromuscular disorder causing infant death in half of all patients. Homozygous absence of the survival motor neuron gene (SMN1) is the primary cause of SMA, while SMA severity is mainly determined by the number of SMN2 copies. One SMN2 copy produces only about 10% of full-length protein identical to SMN1, whereas the majority of SMN2 transcripts is aberrantly spliced due to a silent mutation within an exonic splicing enhancer in exon 7. However, correct splicing can be restored by over-expression of the SR-like splicing factor Htra2-beta 1. We show that in fibroblast cultures derived from SMA patients treated with therapeutic doses (0.5-500 microM) of valproic acid (VPA), the level of full-length SMN2 mRNA/protein increased 2- to 4-fold. Importantly, this up-regulation of SMN could be most likely attributed to increased levels of Htra2-beta 1 which facilitates the correct splicing of SMN2 RNA as well as to an SMN gene transcription activation. Especially at low VPA concentrations, the restored SMN level depended on the number of SMN2 copies. Moreover, VPA was able to increase SMN protein levels through transcription activation in organotypic hippocampal brain slices from rats. Finally, VPA also increased the expression of further SR proteins, which may have important implications for other disorders affected by alternative splicing. Since VPA is a drug highly successfully used in long-term epilepsy therapy, our findings open the exciting perspective for a first causal therapy of an inherited disease by elevating the SMN2 transcription level and restoring its correct splicing.

Animals↗
PubMed2003

Classical infantile spinal muscular atrophy with SMN deficiency causes sensory neuronopathy.

OBJECTIVE: Classic infantile spinal muscular atrophy (SMA) is believed to be a purely motor disorder, affecting neurons of the spinal anterior horn and nuclei of the lower cranial nerves. Other organ malformations or peripheral nerve involvement have been regarded as exclusion criteria for infantile SMA. Whether SMN protein deficiency can also lead to loss of sensory neurons has not been systematically addressed. METHODS: The authors evaluated the sural nerve biopsies of 19 patients with infantile SMA of varying severity. The diagnosis of SMA was confirmed by the presence of a homozygous deletion of the SMN1 gene in all patients. RESULTS: In seven unrelated infants with SMA type I, axonal degeneration of the sural nerve was noted. Five patients showed abnormal sensory conduction, thus prompting sural nerve biopsy. Sural nerves showed different degrees of axonal loss: fiber density ranged from 3.482 to 22.076/mm2 and was markedly reduced in four patients. There was no evidence of primary demyelination: the ratio of total myelinated fiber thickness to axon diameter (g-ratio) was normal in the patients examined. In seven patients with SMA II and five patients with SMA III, no sural nerve alterations were seen, and conduction velocity was normal. In addition to SMN1 gene deletions, homozygous NAIP gene deletions were detected in six out of seven infants with peripheral neuropathy, whereas there was no evidence of a large deletion including the multicopy markers C212 and Ag1-CA in two out of three families tested. CONCLUSIONS: In this series of patients with SMA I through III who underwent sural nerve biopsy, there was significant sensory nerve pathology in severely affected patients with SMA type I, whereas there were no sensory nerve alterations clinically or morphologically in patients with milder SMA type II or III.

Axons↗
PubMed2001

Co-regulation of survival of motor neuron (SMN) protein and its interactor SIP1 during development and in spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by the degeneration of motor neurons in the spinal cord. The disease is caused by mutations of the survival of motor neuron 1 gene (SMN1), resulting in a reduced production of functional SMN protein. A major question unanswered thus far is why reduced amounts of ubiquitously expressed SMN protein specifically cause the degeneration of motor neurons without affecting other somatic cell types. In a first attempt to address this issue we have investigated the Smn interacting protein 1 (Sip1), with an emphasis on its developmental expression and subcellular distribution in spinal motor neurons in relation to Smn. By confocal immunofluorescence studies we provide evidence that a significant amount of Smn does not co-localize with Sip1 in neurites of motor neurons, indicating that Smn may exert motor neuron-specific functions that are not dependent on Sip1. Sip1 is highly expressed in the spinal cord during early development and expression decreases in parallel with Smn during postnatal development. Strikingly, reduced production of Smn as observed in cell lines derived from SMA patients or in a mouse model for SMA coincides with a simultaneous reduction of Sip1. The finding that expression of Sip1 and Smn is tightly co-regulated, together with the unique localization of Smn in neurites, may help in understanding the motor neuron-specific defects observed in SMA patients.

Amino Acid Sequence↗
PubMed2001

Best practice guidelines for molecular analysis in spinal muscular atrophy.

With a prevalence of approximately 1/10 000, and a carrier frequency of 1/40-1/60 the proximal spinal muscular atrophies (SMAs) are among the most frequent autosomal recessive hereditary disorders. Patients can be classified clinically into four groups: acute, intermediate, mild, and adult (SMA types I, II, III, and IV, respectively). The complexity and instability of the genomic region at chromosome 5q13 harbouring the disease-causing survival motor neuron 1 (SMN1) gene hamper molecular diagnosis in SMA. In addition, affected individuals with SMA-like phenotypes not caused by SMN1, and asymptomatic individuals with two mutant alleles exist. The SMN gene is present in at least one telomeric (SMN1) and one centromeric copy (SMN2) per chromosome in normal (non-carrier) individuals, although chromosomes containing more copies of SMN1 and/or SMN2 exist. Moreover, the two SMN genes (SMN1 and SMN2) are highly homologous and contain only five base-pair differences within their 3' ends. Also, a relatively high de novo frequency is present in SMA. Guidelines for molecular analysis in diagnostic applications, carrier detection, and prenatal analysis using direct and indirect approaches are described. Overviews of materials used in the molecular diagnosis as well as Internet resources are included.

Cyclic AMP Response Element-Binding Protein↗
PubMed2000

The transcription factor-like nuclear regulator (TFNR) contains a novel 55-amino-acid motif repeated nine times and maps closely to SMN1.

The transcription factor-like nuclear regulator (TFNR) is a novel human gene that maps on 5q13, distal to the duplicated region that includes SMN1, the spinal muscular atrophy (SMA) determining gene. The location of TFNR allowed us to design an evolutionary model of the SMA region. The 9.5-kb TFNR transcript is highly expressed in cerebellum and weakly in all other tissues tested. TFNR encodes a protein of 2254 amino acids (aa) and contains nine repeats of a novel 55-aa motif, of yet unknown function. The coding region is organized in 32 exons. Alternative splicing of exon 15 results in a truncated protein of 796 aa. TFNR comprises a series of polypeptides that range from 55 to 250 kDa. Immunocytological studies showed that the TFNR protein is present exclusively in the nucleus, where it is concentrated in several nuclear structures. Amino acids 155-474 show significant homology to TFC5, a subunit of the yeast transcription factor TFIIIB, suggesting that TFNR is a putative transcription factor. Based on its proximity to SMN1 and its expression pattern, TFNR may be a candidate gene for atypical forms of SMA with cerebral atrophy and axonal neuropathy that have been shown to carry large deletions in the SMA region.

Alternative Splicing↗
PubMed2000

Htra2-beta 1 stimulates an exonic splicing enhancer and can restore full-length SMN expression to survival motor neuron 2 (SMN2).

Spinal muscular atrophy (SMA), a common motor neuron disease in humans, results from loss of functional survival motor neuron (SMN1) alleles. A nearly identical copy of the gene, SMN2, fails to provide protection from SMA because of a single translationally silent nucleotide difference in exon 7. This likely disrupts an exonic splicing enhancer and causes exon 7 skipping, leading to abundant production of a shorter isoform, SMN2Delta7. The truncated transcript encodes a less stable protein with reduced self-oligomerization activity that fails to compensate for the loss of SMN1. This report describes the identification of an in vivo regulator of SMN mRNA processing. Htra2-beta1, an SR-like splicing factor and ortholog of Drosophila melanogaster transformer-2, promoted the inclusion of SMN exon 7, which would stimulate full-length SMN2 expression. Htra2-beta1 specifically functioned through and bound an AG-rich exonic splicing enhancer in SMN exon 7. This effect is not species-specific as expression of Htra2-beta1 in human or mouse cells carrying an SMN2 minigene dramatically increased production of full-length SMN2. This demonstrates that SMN2 mRNA processing can be modulated in vivo. Because all SMA patients retain at least one SMN2 copy, these results show that an in vivo modulation of SMN RNA processing could serve as a therapeutic strategy to prevent SMA.

Animals↗
PubMed2000

An update of the mutation spectrum of the survival motor neuron gene (SMN1) in autosomal recessive spinal muscular atrophy (SMA).

Spinal muscular atrophy (SMA) is characterized by degeneration of motor neurons in the spinal cord, causing progressive weakness of the limbs and trunk, followed by muscle atrophy. SMA is one of the most frequent autosomal recessive diseases, with a carrier frequency of 1 in 50 and the most common genetic cause of childhood mortality. The phenotype is extremely variable, and patients have been classified in type I-III SMA based on age at onset and clinical course. All three types of SMA are caused by mutations in the survival motor neuron gene (SMN1). There are two almost identical copies, SMN1 and SMN2, present on chromosome 5q13. Only homozygous absence of SMN1 is responsible for SMA, while homozygous absence of SMN2, found in about 5% of controls, has no clinical phenotype. Ninety-six percent of SMA patients display mutations in SMN1, while 4% are unlinked to 5q13. Of the 5q13-linked SMA patients, 96.4% show homozygous absence of SMN1 exons 7 and 8 or exon 7 only, whereas 3. 6% present a compound heterozygosity with a subtle mutation on one chromosome and a deletion/gene conversion on the other chromosome. Among the 23 different subtle mutations described so far, the Y272C missense mutation is the most frequent one, at 20%. Given this uniform mutation spectrum, direct molecular genetic testing is an easy and rapid analysis for most of the SMA patients. Direct testing of heterozygotes, while not trivial, is compromised by the presence of two SMN1 copies per chromosome in about 4% of individuals. The number of SMN2 copies modulates the SMA phenotype. Nevertheless, it should not be used for prediction of severity of the SMA.

Amino Acid Sequence↗
PubMed2000

Exclusion of Htra2-beta1, an up-regulator of full-length SMN2 transcript, as a modifying gene for spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by homozygous mutations of the survival motor neuron gene 1 (SMN1). In rare cases sibs with identical 5q13-homologs and identical SMN1 mutations can show variable phenotypes from unaffected to affected, suggesting the influence of modifying genes. SMN is part of an 800 kDa macromolecular complex that plays an essential role in snRNP biogenesis and pre-mRNA splicing. Due to a single nucleotide difference within SMN1 exon 7 that disrupts an exonic splicing enhancer (ESE), SMN2, a nearly identical copy of SMN1, predominantly expresses alternatively spliced transcripts lacking exon 7, whereas SMN1 mainly produces full-length transcripts. The SR-like trans-acting splicing factor Htra2-beta1 was shown to interact with this ESE and to restore full-length SMN2 expression in vivo in a concentration-dependent manner. Since Htra2-beta1 prevents skipping of exon 7 it is obvious to ask whether mutations within Htra2-beta1 are responsible for the intrafamilial variability of the SMA phenotype. We sequenced either RT-PCR products or genomic DNA covering the complete coding region of Htra2-beta1 as well as the putative promoter of 36 sibs belonging to 15 SMA families with discordant phenotypes but identical genotypes. Neither a mutation nor a polymorphism was found within Htra2-beta1. Additionally, we performed quantitative analysis of Htra2-beta isoforms from 26 sibs without identifying any significant difference between phenotypically discordant sibs. Based on these data, we suggest that the intrafamilial phenotypic variability in SMA families is not caused by polymorphic variants or transcription differences within Htra2-beta1.

Genetic Variation↗
PubMed2000

An essential SMN interacting protein (SIP1) is not involved in the phenotypic variability of spinal muscular atrophy (SMA).

The survival motor neuron (SMN) protein and the SMN interacting protein 1 (SIP1) are part of a 300 kD protein complex with a crucial role in snRNP biogenesis and pre-mRNA splicing. Both proteins are colocalised in nuclear structures called gems and in the cytoplasm. Approximately 96% of patients with autosomal recessive spinal muscular atrophy (SMA) show mutations in the SMN1 gene, while about 4% fail to show any mutation, despite a typical SMA phenotype. Additionally, sibs with identical 5q13 homologs and homozygous absence of SMN1 can show variable phenotypes which suggest that SMA is modified by other, yet unknown factors. Since both genes, SMN1 and SIP1, belong to the same pathway and are part of the same protein complex, it is obvious to ask whether mutations within SIP1 are responsible for both the phenotypic variability and the appearance of non-SMN mutated SMA patients. First, we identified the chromosomal location of SIP1 and assigned it to chromosomal region 14q13-q21 by fluorescence in situ hybridisation. No SMA related disorder has yet been assigned to this chromosomal region. Next, we determined the exon-intron structure of the SIP1 gene which encompasses 10 exons and identified five transcription isoforms. We sequenced either RT-PCR products or genomic DNA covering the complete coding region from 23 typical SMA patients who had failed to show any SMN1 mutation. No mutation and no polymorphism was found within SIP1. Additionally, we sequenced RT-PCR products or genomic fragments of the entire SIP1 coding region from 26 sibs of 11 SMA families with identical genotypes (delta7SMN/delta7SMN or delta7SMN/other mutation) but different phenotypes and again no mutation was found. Finally, we performed quantitative analysis of RT-PCR products from the same 26 sibs. No difference in expression level of the five isoforms among phenotypically variable sibs was observed. Based on these data, we suggest that neither the phenotypic variability nor the 5q-unlinked SMA are caused by mutations within SIP1.

Alternative Splicing↗
PubMed2000

The critical incident stress debriefing process for the Los Angeles County Fire Department: automatic and effective.

Los Angeles County Fire Department has one of the oldest Critical Incident Stress Management (CISM) programs in the country. One core component for the LACoFD has been the Critical Incident Stress Debriefing (CISD). Two important questions for the emergency managers are: 1) Do individuals find a significant difference in symptom reduction for events that were debriefed? 2) Does helpfulness of a debriefing for a specific individual correlate with recommending the process for others? A Department-wide evaluative survey was conducted in 1996 to determine the satisfaction and effectiveness of the debriefing program. Individuals reported a significant difference in the speed of symptom reduction for incidents that were debriefed versus incidents that were not debriefed. The majority of individuals would recommend the debriefing process to others regardless of whether they personally found the process helpful or not. Based on this, the recommendations are to continue the debriefing process for specific events and to make the process mandatory; furthermore, it is recommended that the term "mandatory" be changed to "automatic." By using the term "automatic," debriefings become standard operating procedures. By doing so, a method to protect the psychological welfare of emergency personnel becomes as automatic as putting on safety protection equipment [International Journal of Emergency Mental Health, 2000, 2(4), 249-257].

Adaptation, Psychological↗
PubMed1999

Comparative sequence analysis of the mouse and human Lgn1/SMA interval.

Human chromosome 5q11.2-q13.3 and its ortholog on mouse chromosome 13 contain candidate genes for an inherited human neurodegenerative disorder called spinal muscular atrophy (SMA) and for an inherited mouse susceptibility to infection with Legionella pneumophila (Lgn1). These homologous genomic regions also have unusual repetitive organizations that create practical difficulties in mapping and raise interesting issues about the evolutionary origin of the repeats. In an attempt to analyze this region in detail, and as a way to identify additional candidate genes for these diseases, we have determined the sequence of 179 kb of the mouse Lgn1/SMA interval. We have analyzed this sequence using BLAST searches and various exon prediction programs to identify potential genes. Since these methods can generate false-positive exon declarations, our alignments of the mouse sequence with available human orthologous sequence allowed us to discriminate rapidly among this collection of potential coding regions by indicating which regions were well conserved and were more likely to represent actual coding sequence. As a result of our analysis, we accurately mapped two additional genes in the SMA interval that can be tested for involvement in the pathogenesis of SMA. While no new Lgn1 candidates emerged, we have identified new genetic markers that exclude Smn as an Lgn1 candidate. In addition to providing important resources for studying SMA and Lgn1, our data provide further evidence of the value of sequencing the mouse genome as a means to help with the annotation of the human genomic sequence and vice versa.

Animals↗
PubMed1999

A single nucleotide in the SMN gene regulates splicing and is responsible for spinal muscular atrophy.

SMN1 and SMN2 (survival motor neuron) encode identical proteins. A critical question is why only the homozygous loss of SMN1, and not SMN2, results in spinal muscular atrophy (SMA). Analysis of transcripts from SMN1/SMN2 hybrid genes and a new SMN1 mutation showed a direct relationship between presence of disease and exon 7 skipping. We have reported previously that the exon-skipped product SMNDelta7 is partially defective for self-association and SMN self-oligomerization correlated with clinical severity. To evaluate systematically which of the five nucleotides that differ between SMN1 and SMN2 effect alternative splicing of exon 7, a series of SMN minigenes was engineered and transfected into cultured cells, and their transcripts were characterized. Of these nucleotide differences, the exon 7 C-to-T transition at codon 280, a translationally silent variance, was necessary and sufficient to dictate exon 7 alternative splicing. Thus, the failure of SMN2 to fully compensate for SMN1 and protect from SMA is due to a nucleotide exchange (C/T) that attenuates activity of an exonic enhancer. These findings demonstrate the molecular genetic basis for the nature and pathogenesis of SMA and illustrate a novel disease mechanism. Because individuals with SMA retain the SMN2 allele, therapy targeted at preventing exon 7 skipping could modify clinical outcome.

Alleles↗
PubMed1999

Quantitative analysis of survival motor neuron copies: identification of subtle SMN1 mutations in patients with spinal muscular atrophy, genotype-phenotype correlation, and implications for genetic counseling.

Problems with diagnosis and genetic counseling occur for patients with autosomal recessive proximal spinal muscular atrophy (SMA) who do not show the most common mutation: homozygous absence of at least exon 7 of the telomeric survival motor neuron gene (SMN1). Here we present molecular genetic data for 42 independent nondeleted SMA patients. A nonradioactive quantitative PCR test showed one SMN1 copy in 19 patients (45%). By sequencing cloned reverse-transcription (RT) PCR products or genomic fragments of SMN1, we identified nine different mutations in 18 of the 19 patients, six described for the first time: three missense mutations (Y272C, T274I, S262I), three frameshift mutations in exons 2a, 2b, and 4 (124insT, 241-242ins4, 591delA), one nonsense mutation in exon 1 (Q15X), one Alu-mediated deletion from intron 4 to intron 6, and one donor splice site mutation in intron 7 (c.922+6T-->G). The most frequent mutation, Y272C, was found in 6 (33%) of 18 patients. Each intragenic mutation found in at least two patients occurred on the same haplotype background, indicating founder mutations. Genotype-phenotype correlation allowed inference of the effect of each mutation on the function of the SMN1 protein and the role of the SMN2 copy number in modulating the SMA phenotype. In 14 of 23 SMA patients with two SMN1 copies, at least one intact SMN1 copy was sequenced, which excludes a 5q-SMA and suggests the existence of further gene(s) responsible for approximately 4%-5% of phenotypes indistinguishable from SMA. We determined the validity of the test, and we discuss its practical implications and limitations.

Cyclic AMP Response Element-Binding Protein↗