Result of carrier screening for spinal muscular atrophy among 3049 reproductive-age individuals from Yunnan region / 中华医学遗传学杂志

OBJECTIVE@#To perform carrier screening for spinal muscular atrophy (SMA) among 3049 reproductive-age individuals from Yunnan region and determine the copy number of survival motor neuron (SMN) gene and carrier frequencies.@*METHODS@#Multiplex ligation-dependent probe amplification (MLPA) was used to determine the copy number of exon 7 of SMN1 and SMN2 genes and identify those with a single copy of SMN1 gene. Prenatal diagnosis was performed for couples whom were both found to be SMA carriers.@*RESULTS@#In total 62 SMA carriers were identified among the 3049 subjects, which yielded a carrier frequency of 1 in 49 (2.03%). No statistical difference was found in the carrier frequency between males and females (1.91% vs. 2.30%, P>0.05). Respectively, 1.3% (41/3049) and 0.69% (21/3049) of the carriers were caused by heterozygous deletion and conversion of the SMN1 gene. The average copy number for SMN1 alleles was 1.99. Two couples were found to be both as SMA carriers, for whom the birth of an affected fetus was avoided by prenatal diagnosis.@*CONCLUSION@#No difference was found in the carrier frequency of SMA-related mutations between the two genders in Yunnan region, which was in keeping to an autosomal recessive inheritance pattern. Determination of the carrier frequency for SMA and SMN gene variants may provide a basis for genetic counseling and prenatal diagnosis for the disease.

Supplementary value of denaturing high performance liquid chromatography for routine prenatal diagnosis of spinal muscular atrophy by multiple ligation-dependent probe amplification / 中华医学遗传学杂志

OBJECTIVE@#To explore the feasibility of high performance liquid chromatography (DHPLC) combined with multiple ligation-dependent probe amplification (MLPA) for the prenatal diagnosis of spinal muscular atrophy (SMA).@*METHODS@#Three families who had given birth to children with SMA type I were subjected to prenatal diagnosis. Peripheral blood samples were collected from the three couples, and 10 mL amniotic fluid was taken for each fetus through amniocentesis at 16-24 gestational week. Following DNA extraction, maternal contamination was excluded by STR analysis. Copy numbers of the SMN genes were detected by denaturing high performance liquid chromatography (DHPLC). Relative copy number of SMN1, SMN2 and reference genes was detected with a MLPA P021 assay kit.@*RESULTS@#The three couples were all found to harbor heterozygous deletion of exon 7 of the SMN1 gene by DHPLC. MLPA analysis also suggested that the three couples were all carriers of SMA mutations. The fetus of family 1 harbored homozygous deletion of exons 7 and 8 of the SMN1 gene, in addition with heterozygous deletion of exons 7 and 8 of the SMN2 gene, suggesting that the fetus had SMA. The fetus of family 2 also harbored homozygous deletion of exons 7 and 8 of the SMN1 gene, while the copy number of SMN2 gene was normal, suggesting that the fetus was a SMA patient too. The fetus of family 3 harbored heterozygous deletion of exons 7 and 8 of the SMN1 gene, in addition with heterozygous deletion of exons 7 and 8 of the SMN2 gene, suggesting that the fetus was a carrier.@*CONCLUSION@#DHPLC can effectively screen carriers of SMA mutations. Combined DHPLC and MLPA can provide accurate diagnosis for fetuses with a high risk for SMA.

Association of copy number of SMN1 and SMN2 with clinical phenotypes in children with spinal muscular atrophy / 中国当代儿科杂志

OBJECTIVE@#To study the association of copy number of SMN1 and SMN2 with clinical phenotypes in children with spinal muscular atrophy (SMA).@*METHODS@#A total of 45 children with SMA were enrolled. Multiplex ligation-dependent probe amplification was used to measure the gene copy numbers of SMN1 and SMN2. The association of copy number of SMN1 and SMN2 with clinical phenotypes was analyzed.@*RESULTS@#Of the 45 children with SMA, 42 (93%) had a homozygous deletion of SMN1 exons 7 and 8, and 3 (7%) had a deletion of SMN1 exon 7 alone. No association was found between SMA clinical types and the deletion types of SMN1 exons 7 and 8 (P>0.05). There was a significant difference in the distribution of SMN2 gene copy numbers between the children with SMA and the healthy children (P<0.05). The children with SMA usually had two or three copies of SMN2 gene, while the healthy children usually had one or two copies of SMN2 gene. There was a significant difference in the distribution of SMN2 copy numbers among the children with different SMA clinical types (P<0.05). The children with two copies of SMN2 gene had a significantly lower age of onset than those with three or four copies. Most of the children with type I SMA had two or three copies of SMN2 gene. Most of the children with type II SMA had three copies of SMN2 gene. Most of the children with type III SMA had three or four copies of SMN2 gene. Children with a higher copy number of SMN2 gene tended to have an older age of onset and better motor function and clinical outcome, and there was a significant association between SMN2 gene copy number and clinical outcome (P<0.05).@*CONCLUSIONS@#The SMN2 gene can reduce the severity of SMA via the dosage compensation effect. SMN2 copy number is associated with the phenotype of SMA, and therefore, it can be used to predict disease severity.

Diagnosis of Spinal Muscular Atrophy: A Simple Method for Quantifying the Relative Amount of Survival Motor Neuron Gene 1/2 Using Sanger DNA Sequencing / 中华医学杂志(英文版)

Background@#Spinal muscular atrophy (SMA) is caused by homozygous deletion or compound heterozygous mutation of survival motor neuron gene 1 (SMN1), which is the key to diagnose SMA. The study was to establish and evaluate a new diagnostic method for SMA.@*Methods@#A total of 1494 children suspected with SMA were enrolled in this study. Traditional strategy, including multiplexed ligation-dependent probe amplification (MLPA) and TA cloning, was used in 1364 suspected SMA children from 2003 to 2014, and the 130 suspected SMA children were tested by a new strategy from 2015 to 2016, who were also verified by MLPA combined with TA cloning. The SMN1 and SMN2 were simultaneously amplified by polymerase chain reaction using the same primers. Mutation Surveyor software was used to detect and quantify the SMN1 variants by calculating allelic proportions in Sanger sequencing. Finally, turnaround time and cost of these two strategies were compared.@*Results@#Among 1364 suspected SMA children, 576 children had SMN1 homozygous deletion and 27 children had SMN1 compound heterozygous mutation. Among the 130 cases, 59 had SMN1 homozygous deletion and 8 had heterozygous deletion: the SMN1-specific peak proportion on exon 7 was 34.6 ± 1.0% and 25.5 ± 0.5%, representing SMN1:SMN2 to be 1:2 and 1:3, respectively. Moreover, five variations, including p.Ser8Lysfs *23 (in two cases), p.Leu228*, p.Pro218Hisfs *26, p.Ser143Phefs*5, and p.Tyr276His, were detected in 6/8 cases with heterozygous deletion, the mutant allele proportion was 31.9%, 23.9%, 37.6%, 32.8%, 24.5%, and 23.6%, which was similar to that of the SMN1-specific site on exon 7, suggesting that those subtle mutations were located in SMN1. All these results were consistent with MLPA and TA cloning. The turnaround times of two strategies were 7.5 h and 266.5 h, respectively. Cost of a new strategy was only 28.5% of the traditional strategy.@*Conclusion@#Sanger sequencing combined with Mutation Surveyor analysis has potential application in SMA diagnosis.

Detection of homozygous deletions in spinal muscular atrophy with genomic DNA sequencing / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>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).</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>Genomic DNA sequencing is a rapid, accurate and economic method for the diagnosis of homozygous deletion of SMA.</p>

Carrier screening for spinal muscular atrophy in 4719 pregnant women in Shanghai region / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>Spinal muscular atrophy (SMA) is a common and fatal autosomal recessive disorder. Approximately 94% of SMA patients are caused by homozygous deletion of SMN1 gene. SMA carrier screening is recommended considering the high carrier frequency (1 in 35-50) as well as severity of the disease.</p><p><b>METHODS</b>A prospective population-based cohort study was carried out on 4719 pregnant women from Shanghai region. Copy numbers of SMN1 and SMN2 genes were effectively determined with denaturing high performance liquid chromatography (DHPLC) technique. The method has detected 94% of SMA cases with deletion or conversion of the SMN1 genes.</p><p><b>RESULTS</b>Ninety SMA carriers with only one copy of the SMN1 gene were identified among the 4719 pregnant woman. The carrier rate was 1.9%. Respectively, 1.2% and 0.6% of the carriers were caused by SMN1 gene deletion and SMN1 gene conversion.</p><p><b>CONCLUSION</b>Through this study, we have determined the frequency of SMA mutation carriers in a population of pregnant women. The result may provide a basis for genetic counseling in order to reduce the rate of SMA affected births.</p>

Allele-specific PCR for a cost-effective & time-efficient diagnostic screening of spinal muscular atrophy.

Background & objectives: Genetic diagnosis of spinal muscular atrophy (SMA) is complicated by the presence of SMN2 gene as majority of SMA patients show absence or deletion of SMN1 gene. PCR may amplify both the genes non selectively in presence of high amount of DNA. We evaluated whether allelespecific PCR for diagnostic screening of SMA is reliable in the presence of high amount of genomic DNA, which is commonly used when performing diagnostic screening using restriction enzymes. Methods: A total of 126 blood DNA samples were tested in amounts ranging 80-200 ng, referred for the genetic diagnosis of SMA using both conventional PCR-RFLP and allele-specific PCR. Results: The results from both methods showed agreement. Further, allele-specific PCR was found to be a time-efficient and cost-effective method. Interpretation & conclusions: Our study demonstrated the accuracy of our allele-specific PCR and the results were comparable compatible with that of PCR-RFLP, indicating its practical application in SMA diagnostic screening.

Homozygous SMN2 Deletion is a Major Risk Factor among Twenty-Five Korean Sporadic Amyotrophic Lateral Sclerosis Patients

PURPOSE: The association between survivor motor neuron (SMN) gene deletion and spinal muscular atrophy suggests that sporadic amyotrophic lateral sclerosis (sALS) may be related to SMN deletion. We examined the association between the SMN genotype and susceptibility to and severity of sALS. MATERIALS AND METHODS: We genotyped the copy number of SMN1 and SMN2 in 25 patients diagnosed with sporadic ALS and 100 healthy subjects in a Korean population. Onset age and medical research council (MRC) scale were compared among patients according to SMN1 : SMN2 genotypes. RESULTS: There was a significantly higher incidence of homozygous deletion of SMN2 (SMN1 : SMN2 genotype, 2 : 0) in sALS patients (20%) than in the normal controls (2%) (p<0.001). The onset age for patients with homozygous deletion of SMN2 (2 : 0) was significantly younger (34+/-15.38 years) than that of patients with 2 : 1, 2 : 2 and 2 : 3 of the SMN1 : SMN2 genotype (59.5+/-5.09; 52.69+/-16.46 and 50+/-0.00 years) (p=0.049). The ratio of patients with an MRC scale above G4- was smaller in the 2 : 0 genotype (40%) than in the 2 : 1, 2 : 2 and 2 : 3 genotypes (83.3%, 100% and 100%) (p=0.02). CONCLUSION: The homozygous SMN2 deletion (2 : 0) was statistically more frequent and associated with earlier onset age and lower MRC scale in Korean sALS patients. These suggest that SMN2 deletion may be one of the factors associated with susceptibility to and severity of sALS in a Korean population.

Compound heterozygous mutation in two unrelated cases of Chinese spinal muscular atrophy patients / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Infantile proximal spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder. Approximately 90% - 95% cases of SMA result from homozygous deletion of survival motor neuron gene 1 (SMN1) and 5% cases are caused by compound heterozygous mutation (a SMN1 deletion on one allele and a subtle mutation on the other allele).</p><p><b>METHODS</b>In this research, two unrelated patients were clinically diagnosed according to the criteria of proximal SMA. Genetic diagnosis was performed to detect the homozygous deletion of exon 7 of SMN1 by PCR-restriction fragment length polymorphism (RFLP) and genomic sequencing. Multiplex ligation-dependent probe amplification (MLPA) analysis was carried out to measure copy numbers of SMN1, SMN2 and neuronal apoptosis inhibitor protein (NAIP) in the patients. Further sequencing of SMN1 allele-specific PCR (AS-PCR) and SMN1 clones were also performed to analyze the point mutation of SMN1 gene. Additionally, the pedigree analysis of these two families was carried out to identify the transmission of the mutation.</p><p><b>RESULTS</b>The inconsistent results using PCR-RFLP and genomic sequencing showed homozygous deletion of exon 7 of SMN1 and heterozygous deletion accompanied with a suspicious mutation in SMN1 gene, respectively. MLPA analysis of these two cases exhibited one SMN1 copy deletion. One identical c.863G > T (p.Arg288Met) mutation was found in two cases by sequencing the SMN1 clones, which confirmed that both cases were SMA compound heterozygotes. One case showed partial conversion to form hybrid SMN (SMN2 I7/SMN1 E8) identified by clones sequencing and another case carrying 3 SMN2 implied complete conversion from SMN1 to SMN2.</p><p><b>CONCLUSION</b>p.Arg288Met is more a disease-causing mutation than a polymorphism variation, and children with this mutation may have more severe phenotypes.</p>

Point mutation analysis of SMN1 gene in patients with spinal muscular atrophy / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To identify the point mutations in survival motor neuron gene 1 SMN1 gene and confirm the existence of compound heterozygous mutations in Chinese patients with spinal muscular atrophy (SMA).</p><p><b>METHODS</b>Three unrelated patients were diagnosed and clinically typed according to the criteria of proximal SMA established by the International SMA Consortium. Multiplex ligation-dependent probe amplification (MLPA) analysis was carried out to measure the copy numbers of SMN1, SMN2 and neuronal apoptosis inhibitory protein gene (NAIP)in the patients. The point mutation analysis of SMN1 gene was performed by reversed transcript-polymerase chain reaction (RT-PCR) and cloning sequencing. The MLPA assay and point mutation analysis were also performed in the family members to confirm the transmission of the mutations.</p><p><b>RESULTS</b>Two point mutations were identified in the present study, i.e., the p.Leu228X in one patient and p.Arg288Met in two patients. The mutation p.Arg288Met was first reported in Chinese and p.Leu228X was first reported in Mainland Chinese. The case carrying p.Leu228X mutation was diagnosed as SMA I with 2 copies of SMN2, and the cases with p.Arg288Met were diagnosed as SMA I and SMA II , respectively, with 3 copies of SMN2 gene.</p><p><b>CONCLUSION</b>The mutations p.Leu228X and p.Arg288Met caused severe clinical phenotypes, SMA I or SMA II. This study suggested that the compound heterozygous mutations of SMN1 existed in Chinese SMA patients, which was rarely reported previously in Chinese. It was necessary to detect the point mutation in SMN1 for genetic diagnosis of those patients with heterozygous deletion of SMN1, which would be beneficial to prenatal diagnosis and genetic counseling in these families.</p>

Analysis of survival motor neuron gene conversion in patients with spinal muscular atrophy / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>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.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>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.</p>

Determination of SMN1 and SMN2 Copy Numbers in a Korean Population using Multiplex Ligation-dependent Probe Amplification / 대한진단검사의학회지

Determination of the copy number of the survival motor neuron (SMN) gene is important for detecting spinal muscular atrophy (SMA) carriers and compound heterozygous patients. Multiplex ligationdependent probe amplification (MLPA) assay is a simple and efficient technique used for detecting variations in the copy numbers of different genes. Race- and ethnicity-based variation in the SMA carrier frequency and the '2+0' genotype of SMN1 are important factors that should be considered when estimating the risk of being an SMA carrier. Since SMN2 plays a disease-modifying role, accurate determination of SMN2 copy numbers in SMA patients can serve as a useful prognostic tool. Therefore, information on the SMN2 genotype distributions in normal populations will be helpful in selecting appropriate reference samples for MLPA analysis. To determine SMA carrier frequencies and SMN genotype distribution, we determined the copy numbers of SMN1 and SMN2 genes using the MLPA assay in 100 unrelated Korean individuals with no family history of SMA. The frequency of SMA carriers in the Korean population appears to be 1 in 50, which indicates that the prevalence of SMA among Koreans is the same as that among individuals in the Western countries. Two of the 100 normal individuals enrolled in this study showed 3 copies of the SMN1 gene. Therefore, 1.0% of the 198 normal alleles in this population was estimated to be 2-copy alleles ('2+0' genotype). SMN2 copy numbers showed a high degree of individual variation. Our results showed that 64% of the individuals had 2 copies of SMN2, but 36% individuals had between 0, 1, or 3 copies of the gene.

Deletions in the survival motor neuron gene in Iranian patients with spinal muscular atrophy

<p><b>INTRODUCTION</b>Spinal muscular atrophy (SMA) is a common neuromuscular disorder with progressive paralysis caused by the loss of alpha-motor neurons in the spinal cord. The survival motor neuron (SMN) protein is encoded by 2 genes, SMN1 and SMN2. The most frequent mutation is the biallelic deletion of exon 7 of the SMN1 gene. In SMA, SMN2 cannot compensate for the loss of SMN1, due to the exclusion of exon 7. The aim of our study was to estimate the frequency of the common SMN1 exon 7 deletion in patients referred to our centre for carrier detection and prenatal diagnosis.</p><p><b>MATERIALS AND METHODS</b>We performed the detection of exon 7 deletion of the SMN1 gene for the affected patients and fetuses suspected to have SMA.</p><p><b>RESULTS</b>Of 243 families, 195 were classified as SMA type I, 30 as type II, and 18 as type III according to their family histories. The analysis of exon 7 deletion among living affected children showed that 94% of the patients with SMA type I, 95% with type II families and 100% with type III had homozygous deletions. Of the prenatal diagnoses, 21 (22.8%) of the 92 fetuses were found to be affected and these pregnancies were terminated.</p><p><b>CONCLUSIONS</b>The homozygosity frequency for the deletion of SMN1 exon 7 for all 3 types was (94%), similar to those of Western Europe, China, Japan and Kuwait.</p>

Prenatal diagnosis of 5 fetuses with high risk of developing spinal muscular atrophy / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To perform prenatal diagnosis for 5 pregnant women who had given birth to children with spinal muscular atrophy (SMA).</p><p><b>METHODS</b>Thirty to forty mililiters of amniotic fluid was obtained by amniocentesis under ultrasonic monitoring. DNA was extracted directly from sediment of amniotic fluid. Short tandem repeat (STR) profiling was carried out to evaluate the contamination of amniotic DNA by maternal genomic DNA. Two methods, PCR-restriction fragment length polymorphism (PCR-RFLP) and allele-specific PCR, were used to analyze exon 7 of SMN gene from amniotic DNA.</p><p><b>RESULTS</b>Comparing the 16 STR sites of each fetus with those of his/her parents, there was no or little contamination of amniotic DNA by maternal genomic DNA. In conventional PCR-RFLP, part of the PCR product (189 bp) from amniotic DNA of fetus A, C, or D remained intact after digestion with Dra I, while the PCR product from amniotic DNA of fetus B or E was completely digested by Dra I. In allele-specific PCR, exon 7 of both SMN1 and SMN2 gene could be seen when amniotic DNA of fetuses A, C, or D was analyzed, while only exon 7 of SMN2 could be seen when amniotic DNA of fetuses B or E was analyzed.</p><p><b>CONCLUSION</b>Homozygous deletion of SMN1 is not detected in fetuses A, C, and D, predicting that the risk of developing SMA after birth would be extremely low. Homozygous deletion of SMN1 was present in fetuses B and E suggesting high risk of developing SMA after birth.</p>

The study of the correlation between the clinical phenotype of spinal muscular atrophy and SMN2 gene copy number / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To detect the correlation between the clinical phenotype of spinal muscular atrophy (SMA) and survival motor neuron gene (SMN2) copy number.</p><p><b>METHODS</b>The SMN2 gene copy numbers of 57 different types of SMA were detected by real-time fluorescence quantitative PCR method with TaqMan technique.</p><p><b>RESULTS</b>Average SMN2 copy number was 1.017 +/- 0.090, 2.019+/- 0.080, 3.104+/- 0.170 in predicting one, two, three copy numbers, respectively, and CV was 8.9%, 3.9%, 5.4%, respectively. Average SMN2 copy number was 1.926+/- 0.460, 2.508+/- 0.460, 2.876+/- 0.270, in type I, II and III SMA, respectively. The SMN2 gene copy number in type II and III SMA were higher than that of type I SMA (P < 0.01). The SMN2 gene copy number in type III SMA was higher than that of type II SMA (P < 0.01). 85.72% of type I SMA patients usually had 2 SMN2 copies; 40% and 60% of type II SMA patients had 2 and 3 SMN2 copies, respectively; 82% of type III SMA patients had 3 SMN2 copies.</p><p><b>CONCLUSION</b>There is significant correlation between the change of SMA clinical phenotype and SMN2 cope number. The distributions of the SMN2 gene copy number are various in different types of SMA patients. All types of SMA patients have at least one copy SMN2. The SMN2 gene copy numbers in type II, III SMA are higher than that of type I. All of these findings suggest that the severity of SMA patients depend on the change of the SMN2 copy numbers.</p>

Rapid diagnosis of spinal muscular atrophy using denaturing high-performance liquid chromatography / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To introduce the application of denaturing high-performance liquid chromatography (DHPLC) in the diagnosis of childhood type spinal muscular atrophy (SMA).</p><p><b>METHODS</b>Exon 7 and flanking area of survival motor neuron (SMN) gene were amplified by PCR in 1 standard sample, 25 normal individuals and 25 patients with SMA. The PCR products were then directly loaded onto the DHPLC system after denaturing and annealing. Different DNA segments were separated by changing the concentration of buffer A relative to that of buffer B.</p><p><b>RESULTS</b>Different DNA segments were separable on the DHPLC chromatogram. Three peaks including SMN1/SMN2 heteroduplex peak, SMN2 homoduplex peak and SMN1 homoduplex peak were detected in 23 out of 25 normal individuals. Only SMN1 homoduplex peak was detected in 2 normal individuals and the standard sample, indicating the deletion of SMN2 On the contrary, only the SMN2 homoduplex peak was detected in 22 out of 25 patients with SMA, indicating deletion of SMN1. The three peaks as those of normal individuals were detected in the other 3 patients, indicating no SMN1 or SMN2 deletion.</p><p><b>CONCLUSION</b>As a new technology for diagnosing SMA, DHPLC is sensitive, accurate, rapid and convenient.</p>