- [Show abstract] [Hide abstract] ABSTRACT: Proximal spinal muscular atrophy (SMA) is a common fatal autosomal recessive disorder caused by deletion or mutation of the survival of motor neuron 1 (SMN1). Here, we studied SMA molecular pathology in 653 Chinese patients and found approximately 88.2% with homozygous SMN1 exon 7 deletion and 6.3% with heterozygous exon 7 loss using multiplex ligation-dependent probe amplification. SMN1 variants were detected in 34 patients with heterozygous SMN1 loss by clone sequencing. In 27 of them, 15 variants were identified: five were unreported novel variants [c.-7_9del(p.0), p.Tyr109Cys, p.Ile249Tyrfs*16, p.Tyr272Trpfs*35, and c.835-5T>G], five were previously found only in Chinese patients (p.Ser8Lysfs*23, p.Gln14*, p.Val19Glyfs*21, p.Leu228*, and p.Tyr277Cys), and five were reported in other populations [p.Ala2Gly, p.Gln15*, p.Glu134Lys, p.Ser230Leu, and c.863G>T (r.835_*3del, p.Gly279Glufs*5)]. Variants p.Ser8Lysfs*23 and p.Leu228* were the most common in Chinese SMA. Five variants (p.Ser8Lysfs*23, p.Gln14*, p.Gln15*, p.Val19Glyfs*21, and p.Leu228*) resulted in premature stop codons, likely causing SMN1 mRNA nonsense-mediated decay. The novel variant c.-7_9del (p.0) caused deletion of the translation start codon (AUG), resulting in full-length SMN protein loss. The novel variant c.835-5T>G, located in a splice site, resulted in 90% exon 7 skipping. Our study could facilitate early diagnosis for SMA patients in mutation detection and revealed the specific mutation spectrum of SMN1 in Chinese SMA and high genetic heterogeneity in subtle variants observed between patients from China and Caucasians.
Dataset: Supplementary material
- [Show abstract] [Hide abstract] ABSTRACT: The homozygous loss of the survival motor neuron 1 (SMN1) gene is the primary cause of spinal muscular atrophy (SMA), a neuromuscular degenerative disease. A genetically similar gene, SMN2, which is not functionally equivalent in all SMA patients, modifies the clinical SMA phenotypes. We analyzed the methylation levels of 4 CpG islands (CGIs) in SMN2 in 35 Chinese children with SMA by MassARRAY. We found that three CpG units located in CGI 1 (nucleotides (nt) −871, −735) and CGI 4 (nt +999) are significantly hypomethylated in SMA type III compared with type I or II children after receiving Bonferroni correction. In addition to the differentially methylated CpG unit of nt −871, the methylation level of the nt −290/−288/−285 unit was negatively correlated with the expression of SMN2 full-length transcripts (SMN2-fl). In addition, the methylation level at nt +938 was inversely proportional to the ratio of SMN2-fl and lacking exon 7 transcripts (SMN2-Δ7, fl/Δ7), and was not associated with the SMN2 transcript levels. Thus, we can conclude that SMN2 methylation may regulate the SMA disease phenotype by modulating its transcription.
Dataset: Supplementary material
- [Show abstract] [Hide abstract] ABSTRACT: X‑linked ichthyosis (XLI) is an X‑linked recessive skin disorder generally restricted to males, which arises from mutations in the steroid sulfatase (STS) gene located on Xp22.3. Crigler‑Najjar syndrome (CN‑I) is a rare autosomal recessive disease caused by the homozygous or compound heterozygous mutations in the UPD‑glucuronosyltransferase 1 family, polypeptide A1 (UGT1A1) gene on chromosome 2q37. A male patient was referred to the Department of Medical Genetics with of severe icterus and ichthyosis. The patient and his family members underwent genetic tests related to XLI and CN‑I. Quantitative polymerase chain reaction on genomic DNA was performed to determine the gene copy number, while single nucleotide polymorphism array analysis was conducted to identify deletion mutations. Family pedigree analysis showed that the patient and his two cousins were all affected by ichthyosis, which was in accordance with the inheritance pattern of an X‑linked recessive disease. In addition, the patient's serum bilirubin concentration (>340 mmol/l) was markedly greater than the normal level. The patient presented with kernicterus and phenobarbital treatment was ineffective. The clinical diagnosis of XLI was confirmed molecularly by laboratory evidence of a maternal 1.61 M deletion (including the STS gene) on ChrXp22.31. Coincidentally, the male patient was also confirmed to carry a rare maternal inherited microdeletion (374 Kb) comprising the entire UGT1A1 gene combined with a paternal UGT1A1 mutation (c.1253delT), a causative event of CN‑I. To the best of our knowledge, this study reported for the first time the comorbidity of XLI and CN‑I in a male patient. The results suggested that co‑occurrence of these two recessive diseases in a patient may be incidental.
- [Show abstract] [Hide abstract] ABSTRACT: Kindler syndrome (KS; OMIM 173650) is a rare autosomal recessive skin disorder, which results in symptoms including blistering, epidermal atrophy, increased risk of cancer, and poor wound healing. The majority of mutations of the disease-determining gene (FERMT1 gene) are single nucleotide substitutions, including missense mutations, nonsense mutations, etc. Large deletion mutations are seldom reported. To determine the mutation in the FERMT1 gene associated with a 7-year-old Chinese patient who presented clinical manifestation of KS, we performed direct sequencing of all the exons of FERMT1 gene. For the exons 2–6 without amplicons, we analyzed the copy numbers using quantitative real-time polymerase chain reaction (qRT-PCR) with specific primers. The deletion breakpoints were sublocalized and the range of deletion was confirmed by PCR and direct sequencing. In this study, we identified a new 17-kb deletion mutation spanning the introns 1–6 of FERMT1 gene in a Chinese patient with severe KS phenotypes. Her parents were carriers of the same mutation. Our study reported a newly identified large deletion mutation of FERMT1 gene involved in KS, which further enriched the mutation spectrum of the FERMT1 gene. © 2015, Zhejiang University and Springer-Verlag Berlin Heidelberg.
- [Show abstract] [Hide abstract] ABSTRACT: Proximal spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by deletion or mutation of SMN1 (survival motor neuron 1). SMN exon 7 splicing is regulated by a number of exonic and intronic regulatory sequences and the trans-factors that bind them. Variants located in or near these regulated regions should be evaluated to determine their effect on splicing. We identified the rare variant c.863G>T (r.835_*3del, p.Gly279Glufs*5) in exon 7 of SMN1 in three patients affected with type I or type II SMA. Most of the SMN1 transcripts exhibited complete loss of exon 7 in vivo. The ex vivo splicing assay demonstrated that the variant disrupts inclusion of exon 7 (~85%) in the SMN1 mRNA; replacement with various bases yielded a variety of splicing effects in SMN1 and SMN2 pre-mRNA. The c.863G>T (r.835_*3del, p.Gly279Glufs*5) variant is located in a region that includes binding sites for multiple splicing factors including Tra2β1. Thus, the variant disrupts Tra2β1 binding, but does not affect binding of hnRNP A1. These findings demonstrate how rare variants influence pre-mRNA splicing of SMN and reveal the functional influence of c.863G>T (r.835_*3del, p.Gly279Glufs*5) variant in patients with SMA.European Journal of Human Genetics advance online publication, 30 September 2015; doi:10.1038/ejhg.2015.213.
- [Show abstract] [Hide abstract] ABSTRACT: Objective: To establish a hyperphenylalaninemia related genes screening method using Ion Torrent Personal Genome Machine (PGM) for early detection and differential diagnosis of hyperphenylalaninemia (HPA). Methods: Three children with known HPA mutations and a healthy control were used for setting up the method. Ten children with HPA with known mutations were recruited for validating the method. Ion Ampliseq PCR was used to amplify the 5' and 3' untranslated region, coding sequence, and flanking introns of PAH, GCH1, PTS, QDPR, and PCBD1 genes. After the enrichment with the Ion OneTouch system, the products were sequenced by PGM. Data from the PGM were processed with Torrent Suite v2.2 software package. All variations were confirmed by Sanger sequencing. Results: For the 4 samples, the PGM output was 94.22 Mb, with approximately 99.5% of reads mapping to the target regions. Among these samples, we detected 74 variations (28 positions) including 6 known mutations. Compared with database and results of Sanger sequencing, 55 (18 positions) polymorphisms and 13 (4 positions) false positive calls were confirmed. For the 10 samples, all the known mutations were successfully identified. Conclusion: Ion Torrent PGM sequencing is suitable for screening genetic mutation underlying HPA from the perspective of metabolic pathways, which can meet the clinical demand for individualized diagnosis and treatment.
- [Show abstract] [Hide abstract] ABSTRACT: To explore the diversity of mutations in survival motor neuron gene 1 (SMN1) by analyzing seven cases of partial deletion of SMN1 gene. Seven patients suspected spinal muscular atrophy (SMA) were recruited from 2011 to 2013. Multiplex ligation-dependent probe amplification (MLPA) for genetic testing of SMA was based on the commercially available SALSA MLPA kit P021-A2. Then the data were analyzed by the software Coffalyser.Negative control samples were chosen with two copies of SMN1 and SMN2. Positive control samples were chosen with zero copies of SMN1 and two copies of SMN2. According to the product description (www.mlpa.com): for exon 7 and 8 of SMN1 and SMN2: a ratio of <0.7 indicates 1 copy, a ratio of 0.7-1.3 2 copies, a ratio of 1.3-1.7 3 copies and a ratio of 1.7-2.3 4 copies. For exon 1, 4, 6, 8 of SMN gene (SMN1+SMN2): a ratio <0.4 indicates 1 copy, a ratio of 4.0-0.6 2 copies, a ratio of 0.7-0.9 3 copies and a ratio of 0.9-1.1 4 copies. All samples were analyzed in duplicate. Using MLPA for clinical diagnostics, two types of partial deletions of SMN1were identified in 7 patients.Since exon 8 is not translated and has no effect on the function of SMN protein, exons 1, 4, 6, 7 were targeted.One had an isolated deletion of exon 7 while the other ones were caused by the deletions of exon 1, 4 and 7. These mutations were not detected by conventional diagnostic methods. Both types of partial deletions of SMN1 gene contained a deletion of exon 7. Two types of partial deletions of SMN1 gene indicate that the structure of SMN gene is unstable leading to a variety of mutation forms. But the major cause of SMA lies in a deletion of exon 7 of SMN1 gene.
- [Show abstract] [Hide abstract] ABSTRACT: We evaluated survival motor neuron 2 (SMN2) and neuronal apoptosis inhibitory protein (NAIP) gene copy distribution and the association of copy number with survival in 232 Chinese spinal muscular atrophy (SMA) patients. The SMN2 and NAIP copy numbers correlated positively with the median onset age (r = 0.72 and 0.377). The risk of death for patients with fewer copies of SMN2 or NAIP was much higher than for those with more copies (P < .01). The survival probabilities at 5 years were 5.1%, 90.7%, and 100% for 2, 3, and 4 SMN2 copies and 27.9%, 66.7%, and 87.2% for 0, 1, and 2 NAIP copies, respectively. Our results indicated that combined SMN1-SMN2-NAIP genotypes with fewer copies were associated with earlier onset age and poorer survival probability. Better survival status for Chinese type I SMA might due to a higher proportion of 3 SMN2 and a lower rate of zero NAIP.
- [Show abstract] [Hide abstract] ABSTRACT: Hyperphenylalaninemia (HPA) can be classified into phenylketonuria (PKU) and tetrahydrobiopterin deficiency (BH4D), according to the defect of enzyme activity, both of which vary substantially in severity, treatment, and prognosis of the disease. To set up a fast and comprehensive assay in order to achieve early etiological diagnosis and differential diagnosis for children with HPA, we designed a custom AmpliSeqTM panel for the sequencing of coding DNA sequence (CDS), flanking introns, 5′ untranslated region (UTR) and 3′ UTR from five HPA-causing genes (PAH, PTS, QDPR, GCH1, and PCBD1) using the Ion Torrent Personal Genome Machine (PGM) Sequencer. A standard group of 15 samples with previously known DNA sequences and a test group of 37 HPA patients with unknown mutations were used for assay validation and application, respectively. All variations were confirmed by Sanger sequencing. In the standard group, all the known mutations were detected and were consistent with the results of previous Sanger sequencing. In the test group, we identified mutations in 71 of 74 alleles, with a mutation detection rate of 95.9%. We also found a frame shift deletion p.Ile25Metfs*13 in PAH that was previously unreported. In addition, 1 of 37 in the test group was inconsistent with either the molecular diagnosis or clinical diagnosis by traditional differential methods. In conclusion, our comprehensive assay based on a custom AmpliSeqTM panel and Ion Torrent PGM sequencing has wider coverage, higher throughput, is much faster, and more efficient when compared with the traditional molecular detection method for HPA patients, which could meet the medical need for individualized diagnosis and treatment.
- [Show abstract] [Hide abstract] ABSTRACT: Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder caused by mutations of the survival of motor neuron 1 (SMN1) gene. Approximately 90-95% of SMA patients have a homozygous deletion of SMN1, and 5-10% of patients are believed to have subtle mutations. The molecular diagnosis of SMN1 subtle mutations is hampered by highly homologous SMN2 gene. It is important to establish a rational molecular diagnostic procedure for SMN1 subtle mutations. We analyzed the SMN1 mutations in nine nonhomozygous patients by the following procedures: multiplex ligation-dependent probe amplification, genomic sequencing, T-A cloning on cDNA or genomic level, and/or real-time quantitative analysis. By the above molecular diagnostic procedure, six SMN1 subtle mutations, including c.5C>G(p.Ala2Gly), c.22_23 insA (p.Ser8LysfsX23), c.40G>T(p.Glu14X), c.43C>T(p.Gln15X), c.683T>A(p.Leu228X), and c.56delT(p.Val19GlyfsX21), were identified in nine Chinese patients. p.Glu14X has not been reported previously. Compared with the level of full-length SMN1 transcripts in the healthy carriers (14.1±4.5), the patient with p.Ala2Gly had no significant reduction (13.9±3.64, p=0.955). However, the levels in the patients carrying other mutations were significantly reduced (0.27±0.139 to 13.9±3.64, p=0.000-0.004). We present a reliable and rational diagnostic procedure for SMN1 subtle mutations, which would be helpful in molecular diagnosis of SMA compound heterozygotes. Our work extends the SMN1 mutation spectrum.
- [Show abstract] [Hide abstract] ABSTRACT: Crigler-Najjar syndrome type I (CN-I) is the most severe type of hereditary unconjugated hyperbilirubinemia. It is caused by homozygous or compound heterozygous mutations of the UDP-glycuronosyltransferase gene (UGT1A1) on chromosome 2q37. Two patients clinically diagnosed with CN-I were examined in this paper. We sequenced five exons and their flanking sequences, specifically the promoter region of UGT1A1, of the two patients and their parents. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine the UGT1A1 gene copy number of one patient. In patient A, two mutations, c.239_245delCTGTGCC (p.Pro80HisfsX6; had not been reported previously) and c.1156G>T (p.Val386Phe), were identified. In patient B, we found that this patient had lost heterozygosity of the UGT1A1 gene by inheriting a deletion of one allele, and had a novel mutation c.1253delT (p.Met418ArgfsX5) in the other allele. In summary, we detected three UGT1A1 mutations in two CN-I patients: c.239_245delCTGTGCC (p.Pro80HisfsX6), c.1253delT (p.Met418ArgfsX5), and c.1156G>T (p.Val386Phe). The former two mutations are pathogenic; however, the pathogenic mechanism of c.1156G>T (p.Val386Phe) is unknown.
- [Show abstract] [Hide abstract] ABSTRACT: To detect homozygous deletions of survival motor neuron (SMN) gene with genomic DNA sequencing, and to assess the value of genetic testing for the diagnosis of spinal muscular atrophy (SMA). Polymerase chain reaction (PCR) was used for amplifying SMN gene in 100 SMA patients and 110 controls. Four different bases (g.31957, g.32006, g.32154 and g.32269) between SMN1 and SMN2 within the amplified segments were identified with genomic DNA sequencing. Homozygous deletion of SMN1 or SMN2 was determined by the presence or absence of base peaks at such four sites. Multiplex ligation-dependent probe amplification (MLPA) was carried out to confirm the results of genomic DNA sequencing. In the 100 SMA samples, only SMN2 specific base peaks were detected at the four sites, for which the copy numbers of SMN1 and SMN2 was 0:2 or 0:3, suggesting homozygous deletion of SMN1 gene. By contrast, only SMN1 specific base peaks were detected in 5 samples, for which the ratio of SMN1:SMN2 was 2:0, indicating homozygous deletion of SMN2. At four different sites, SMN1/SMN2 heterozygous peaks were detected in the remaining 105 samples, for which SMN1:SMN2was 2:2, suggesting non-deletion of SMN1 or SMN2. The results of sequencing were consistent with those of MLPA. Genomic DNA sequencing is a rapid, accurate and economic method for the diagnosis of homozygous deletion of SMA.
- [Show abstract] [Hide abstract] ABSTRACT: Angelman syndrome (AS) is a neurobehavioral disorder caused by lack of function of the maternal copy of the ubiquitin-protein ligase E3A (UBE3A) gene. In our study, 49 unrelated patients with classic AS phenotypes were confirmed by methylation-specific PCR (MS-PCR) analysis, short tandem repeat linkage analysis, and mutation screening of the UBE3A gene. Among the Chinese AS patients, 83.7% (41/49) had deletions on maternal chromosome 15q11.2-13. Paternal uniparental disomy, imprinting defects, and UBE3A gene mutations each accounted for 4.1% (2/49). Two AS patients were confirmed by MS-PCR analysis, but the pathogenic mechanism was unknown because their parents' samples were unavailable. Of the 2 described UBE3A gene mutations, i.e., p.Pro400His (c.1199C>A) and p.Asp563Gly (c.1688A>G), the latter has not been reported previously. Mutation transmission analysis showed that the p.Pro400His and p.Asp563Gly mutations originated from asymptomatic mothers. The patients with the maternal deletion showed AS clinical manifestations that were consistent with other studies. However, the incidence of microcephaly (36.7%, 11/30) was lower than that in the Caucasian population (approximately 80%), but similar to that of the Japanese population (34.5%). Our study demonstrated that the occurrence of microcephaly in AS may vary among different populations.
- [Show abstract] [Hide abstract] ABSTRACT: Objective: Early treatment (growth hormone and nutritional support) improves development in infants with Prader-Willi syndrome. This study aimed to evaluate the nutritional and metabolic condition of nine patients who were diagnosed and treated in early infancy. Methods: Nine patients were hospitalized at the age of \xe2\u20ac\xa810 days to 11 months because of severe feeding difficulties, failure to thrive, or developmental delay. The diagnosis of Prader-Willi syndrome was confirmed by fluorescence in situ hybridization or other molecular genetic techniques. Nutritional and metabolic investigations including urinary organic acid analysis, blood amino acid, and acylcarnitine profiles were performed. Results: The diagnosis was made at the mean age of 6.3 months. A deletion of the paternal gene in the 15q11-13 region was detected in all patients. Eight patients had ketosis, seven had malnutrition, five had hyperammonemia, three had liver dysfunction, three had low blood cholesterol level, and two had hypoglycemia. All patients had reduction of serum multiple amino acids and free carnitine. Significant arginine deficiency was found in all patients. Six patients had mildly elevated blood long-chain and very long-chain acylcarnitine. After supplementation with l-arginine, medium-chain fatty acids, l-carnitine, and vitamins, all patients responded with improvement of motor development and nutritional conditions. Four patients were almost caught up on physical and psychomotor development. Conclusions: Patients with Prader-Willi syndrome are in bad metabolic condition in the early period. Early diagnosis and individual nutritional interventions may improve the nutritional and developmental progress and decrease death rate in infancy.
- [Show abstract] [Hide abstract] ABSTRACT: Background Proximal spinal muscular atrophy (SMA) is a common neuromuscular disorder resulting in death during childhood. Around 81 ~ 95% of SMA cases are a result of homozygous deletions of survival motor neuron gene 1 (SMN1) gene or gene conversions from SMN1 to SMN2. Less than 5% of cases showed rare subtle mutations in SMN1. Our aim was to identify subtle mutations in Chinese SMA patients carrying a single SMN1 copy. Methods We examined 14 patients from 13 unrelated families. Multiplex ligation-dependent probe amplification analysis was carried out to determine the copy numbers of SMN1 and SMN2. Reverse transcription polymerase chain reaction (RT-PCR) and clone sequencing were used to detect subtle mutations in SMN1. SMN transcript levels were determined using quantitative RT-PCR. Results Six subtle mutations (p.Ser8LysfsX23, p.Glu134Lys, p.Leu228X, p.Ser230Leu, p.Tyr277Cys, and p.Arg288Met) were identified in 12 patients. The p.Tyr277Cys mutation has not been reported previously. The p.Ser8LysfsX23, p.Leu228X, and p.Tyr277Cys mutations have only been reported in Chinese SMA patients and the first two mutations seem to be the common ones. Levels of full length SMN1 (fl-SMN1) transcripts were very low in patients carrying p.Ser8LysfsX23, p.Leu228X or p.Arg288Met compared with healthy carriers. In patients carrying p.Glu134Lys or p.Ser230Leu, levels of fl-SMN1 transcripts were reduced but not significant. The SMN1 transcript almost skipped exon 7 entirely in patients with the p.Arg288Met mutation. Conclusions Our study reveals a distinct spectrum of subtle mutations in SMN1 of Chinese SMA patients from that of other ethnicities. The p.Arg288Met missense mutation possibly influences the correct splicing of exon 7 in SMN1. Mutation analysis of the SMN1 gene in Chinese patients may contribute to the identification of potential ethnic differences and enrich the SMN1 subtle mutation database.
- [Show abstract] [Hide abstract] ABSTRACT: Mutations in fumarylacetoacetate hydrolase (FAH) gene can lead to tyrosinemia type 1 (HT1), a relatively rare autosomal recessive disorder. To date, no molecular genetic defects of HT1 in China have been described. We investigated a Chinese family with a HT1 child to identify mutations in FAH. DNA sequencing was used for mutations screening in FAH gene. Real-time polymerase chain reaction (PCR) was performed to determine the FAH gene expression level. To confirm the presence of degradation by the nonsense-mediated mRNA decay pathway (NMD), the fragments containing R237X mutations were analyzed by primer introduced restriction analysis-polymerase chain reaction (PIRA-PCR) and cDNA sequencing. Finally, the effects of the mutations reported in this study were predicted by online softwares. A boy aged 3 years and 8 months was diagnosed clinically with HT1 based on his manifestations and biochemical abnormalities. Screening of FAH gene revealed two heterozygous mutations R237X and L375P transmitted from his mother and father respectively. In this pedigree, the amount of FAH mRNA relative to a healthy control was 0.44 for the patient, 0.77 for his mother and 1.07 for his father. Moreover, both PIRA-PCR and cDNA sequencing showed significant reduction of the FAH mRNA with R237X nonsense mutation. The missense mutation of L375P was not reported previously and prediction software showed that this mutation decreased the stability of protein structure and affected protein function. This is the first case of HT1 analyzed by molecular genetics in China. The R237X mutation in FAH down- regulates the FAH gene expression, and the L375P mutation perhaps interrupts the secondary structure of FAH protein.
- [Show abstract] [Hide abstract] ABSTRACT: To explore the applicability and limitation of PCR-restriction fragment length polymorphism (PCR-RFLP) method for genetic diagnosis of spinal muscular atrophy (SMA). PCR-RFLP was applied to detect potential deletion in exons 7 and 8 of SMN1 gene in 935 suspected cases with SMA. Multiplex ligation-dependent probe amplification(MLPA) was carried out to analyze dosage alteration of SMN1 gene in 339 of such cases. To confirm the accuracy of PCR-RFLP method for homozygous and heterozygous deletions detection, the consistency of PCR-RFLP and MLPA results were assessed with a Pearson Chi-square test. Homozygous deletion of exon 7 of SMN1 was detected in 590 suspected cases. The rate of diagnosis was therefore 63.1% (590/935). For the 339 suspected cases, PCR-RFLP and MLPA respectively identified 194 and 196 homozygous deletions in the exon 7 of SMN1 gene, suggesting a good consistency (98.9%)(Chi-square = 0.2, P = 0.88). However, only 4 of 339 cases was found to carry a heterozygous deletion of SMN1 exon 7 by PCR-RFLP, in contrast with 17 detected by MLPA. The consistency only reached 23.5%, for which statistical significance was detected (Chi-square = 8.29, P< 0.01). Although PCR-RFLP is a simple, specific and efficient method for SMA diagnosis, it has obvious limitation for the diagnosis of 5%-10% SMA patients who have carried a compound heterozygous mutation.
- [Show abstract] [Hide abstract] ABSTRACT: To investigate the type and frequency of gene conversion from SMN1 to SMN2 in Chinese patients affected with spinal muscular atrophy (SMA), and to explore the relationship between gene conversion and clinical phenotype. Non-homozygous deletion of SMN1 gene exon 8 was screened among 417 patients with SMN1 exon 7 homozygous deletions. To analyze and verify the types of gene conversion, genomic DNA sequencing, multiplex ligation-dependent probe amplification (MLPA), and gene subcloning and sequencing were carried out. Thirty-one patients (7.4% of all) with non-homozygous deletions of SMN1 exon 8 were detected. Through series of experiments, the fusion genes SMN1/SMN2 in all cases were delineated. Five types of gene conversions were identified, which included SMN2-I7b/SMN1 E8, SMN2-I7a/SMN1 I7b, SMN2-E7/SMN1 I7a, SMN1 I6/SMN2 E7/SMN1 I7a and SMN2-E7/SMN1 I7a/SMN2 I7b. Such conversions were found in the type I-III patients. For 10 patients with type I-III SMA and 3 copies of SMN2 gene produced by conversion, the average survival age was 5 year and 4 months. Partial conversions of SMN1 gene have been found among Chinese SMA patients. The type of conversion and frequency seem to be different from those of other races. Gene conversion to some extent may impact on survival time and rate of SMA patients, especially type I SMA.
Capital institute of PediatricsPeping, Beijing, China