Spinal muscular atrophy (SMA) is a common fatal autosomal recessive genetic disorder in childhood, primarily caused by homozygous deletion of the SMN1 gene. Its main characteristics include the degenerative changes in the anterior horn motor neurons of the spinal cord, leading to symmetrical progressive muscle weakness and atrophy of the proximal limbs. However, SMA patients with the same genetic background often exhibit different degrees of disease severity. In addition to the well-established modifier gene SMN2, the effect of other modifier genes on clinical phenotypes should not be overlooked. This paper reviews the latest advancements in the pathogenic and modifier genes of SMA, aiming to provide a deeper understanding of the pathogenic mechanisms and phenotypic differences in SMA, as well as to offer new strategies and targets for treating this condition.
Humans ; Muscular Atrophy, Spinal/genetics* ; Phenotype ; Survival of Motor Neuron 1 Protein/genetics* ; Genes, Modifier ; Survival of Motor Neuron 2 Protein/genetics*

OBJECTIVE: To assess the carrier frequency of spinal muscular atrophy (SMA) in women of childbearing age in Chongqing and to evaluate prenatal diagnostic outcomes in high-risk couples. METHODS: A total of 17 926 women of childbearing age attending Chongqing Health Center for Women and Children between May 2021 and November 2023 were enrolled, including 3 398 pre-pregnant women and 14 528 pregnant women, all of whom had no clinical phenotype or family history of SMA or related neuromuscular disorders. Real-time quantitative PCR (RT-qPCR) was used to determine the copy number variations in exons 7 and 8 (E7, E8) of the SMN1 gene. High-risk carriers were identified based on the genetic screening results. Multiplex ligation-dependent probe amplification (MLPA) was employed for prenatal diagnosis of fetuses from high-risk couples. This study was approved by the Medical Ethics Committee of Chongqing Health Center for Women and Children (Ethics No.2021-RGI-02). RESULTS: Among the 17 926 women of childbearing age, 298 (1.66%) were identified as heterozygous carriers, including 278 (1.55%) with concurrent deletions of E7 and E8, and 20 (0.11%) with isolated deletions of E7. Seven high-risk couples were identified, six of whom were prenatal couples. Of the two fetuses from these high-risk pregnancies, both exhibited heterozygous deletions of E7 and E8 in the SMN1 gene, while four fetuses showed no abnormalities. CONCLUSION This study provides a comprehensive assessment of the carrier frequency of SMA among women of childbearing age in Chongqing, offering valuable data for the primary and secondary prevention of SMA-related birth defects in the region.
Humans ; Female ; Muscular Atrophy, Spinal/diagnosis* ; Pregnancy ; Prenatal Diagnosis/methods* ; Adult ; Survival of Motor Neuron 1 Protein/genetics* ; Genetic Carrier Screening/methods* ; DNA Copy Number Variations/genetics* ; China ; Genetic Testing ; Heterozygote

OBJECTIVE: To investigate the steady-state mechanism of interconversion between the SMN1 and SMN2 genes in a normal population. METHODS: Fluorescence PCR capillary electrophoresis was employed to assess gene conversion and copy number variation of SMN1 and SMN2 in a cohort of 1,133 healthy individuals (including 256 males and 877 females) recruited between 2019 and 2023. This study was approved by the Ethics Committee of Henan Provincial People's Hospital (Ethics No.: 2019-134). RESULTS: No significant gender difference was observed in the single copy carrying rate of SMN1. The probability of conversion from SMN1 to SMN2 was determined to be 3.2% for females, 2.7% for males, and 3.1% for the overall population. The probability of conversion from SMN2 to SMN1 was found to be 5.5% for females, 6.3% for males, and 5.6% for the overall population. No statistically significant difference was found in the conversion probability between different genders (P > 0.05). Among the 99 cases of gene conversion, the SMN1 gene predominantly exhibited a copy number of 2 (97.0%), with the remainder having 3 copies (3%). The SMN2 gene primarily showed a copy number of 2 (72.7%), with the rest having 1 copy (27.3%). CONCLUSION Gene conversion tends to normalize the copy numbers of both SMN1 and SMN2 genes towards 2. However, SMN1 exhibited a higher priority over SMN2, causing the copy numbers approaching two.
Humans ; Male ; Female ; Survival of Motor Neuron 2 Protein/genetics* ; Survival of Motor Neuron 1 Protein/genetics* ; Gene Conversion ; DNA Copy Number Variations/genetics* ; Adult ; Middle Aged ; Gene Dosage

OBJECTIVE: To carry out carrier screening for Spinal muscular atrophy (SMA) in reproductive-aged individuals from Dongguan region and determine the carrier frequency of SMN1 gene mutations. METHODS: Reproductive-aged individuals who underwent SMN1 genetic screening at the Dongguan Maternal and Child Health Care Hospital from March 2020 to August 2022 were selected as the study subjects. Deletions of exon 7 and 8 (E7/E8) of the SMN1 gene were detected by real-time fluorescence quantitative PCR (qPCR), and prenatal diagnosis was provided for carrier couples by multiple ligation-dependent probe amplification (MLPA). RESULTS: Among the 35 145 subjects, 635 were found to be carriers of SMN1 E7 deletion (586 with heterozygous E7/E8 deletion, 2 with heterozygous E7 deletion and homozygous E8 deletion, and 47 with sole heterozygous E7 deletion). The carrier frequency was 1.81% (635/35 145), with 1.59% (29/1 821) in males and 1.82% (606/33 324) in females. There was no significant difference between the two genders (χ² = 0.497, P = 0.481). A 29-year-old woman was found to harbor homozygous deletion of SMN1 E7/E8, and was verified to have a SMN1∶SMN2 ratio of [0∶4], none of her three family members with a [0∶4] genotype had clinical symptoms. Eleven carrier couples had accepted prenatal diagnosis, and one fetus was found to have a [0∶4] genotype, and the pregnancy was terminated. CONCLUSION This study has determined the SMA carrier frequency in Dongguan region for the first time and provided prenatal diagnosis for carrier couples. The data can provide a reference for genetic counseling and prenatal diagnosis, which has important clinical implications for the prevention and control of birth defects associated with SMA.
Humans ; Child ; Pregnancy ; Male ; Female ; Adult ; Homozygote ; Sequence Deletion ; Prenatal Diagnosis ; Genetic Testing ; Muscular Atrophy, Spinal/genetics* ; Survival of Motor Neuron 1 Protein/genetics* ; Genetic Carrier Screening

OBJECTIVE: To analyze variants of SMN gene in a Chinese pedigree affected with Spinal muscular atrophy (SMA). METHODS: A Chinese pedigree diagnosed at the Nanchang First Hospital in January 2020 was selected as the study subject. Peripheral blood samples were collected for the extraction of DNA. All exons of the SMN gene were detected by multiple ligation-dependent probe amplification (MLPA). Potential variants of the SMN gene were also detected by Whole exome sequencing (WES), and the result was verified by Sanger sequencing. cDNA extracted from fresh blood sample was used as a template to verify the location of variant on the SMN genes. RESULTS: The proband was found to harbor a heterozygous deletion of the SMN1 Exon7+Exon8, and a heterozygous c.81G>A variant. The SMN1 Exon7+Exon8 deletion was inherited from her father and grandmother, whilst the c.81G>A variant was inherited from her mother and maternal grandfather. Her aunt was also a carrier of the heterozygous deletion, while her paternal aunt, her husband, and their daughter were not. cDNA amplification and Sanger sequencing confirmed that the c.81G>A variant was located in the SMN1 gene. CONCLUSION MLPA combined with NGS and Sanger sequencing can identify compound heterozygous variants of the SMN gene in the SMA patients.
Female ; Humans ; Male ; DNA, Complementary ; East Asian People ; Fathers ; Mothers ; Muscular Atrophy, Spinal/diagnosis* ; Pedigree ; Survival of Motor Neuron 1 Protein/genetics*

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron degenerative disease, which is the most common fatal neuromuscular disease in pediatrics with a high carrier frequency and can lead to progressive symmetrical muscle weakness and atrophy of the trunk and limbs. Preimplantation genetic testing (PGT) can be used to prevent the birth of children with SMA effectively. To standardize PGT technologies for SMA, experts from the fields of neurology, pediatrics and reproductive genetics have discussed and drafted this consensus for guiding its clinical application.
Child ; Consensus ; Genetic Testing ; Humans ; Muscular Atrophy, Spinal/genetics* ; Survival of Motor Neuron 1 Protein/genetics*

OBJECTIVE: To carry out prenatal diagnosis for families with high risk for spinal muscular atrophy (SMA) by using multiplex ligation-dependent probe amplification (MLPA). METHODS: Twenty-one families were enrolled. MLPA was used to detect copy numbers of SMN1 and SMN2 genes. Maternal contamination was excluded by using a short tandem repeat method. RESULTS: For 23 fetuses from the 21 families, 14 were identified as carriers, 1 as SMA patient, and 8 as normal. By linkage analysis of parental samples, three individuals were determined as silent (2+0) carriers. CONCLUSION MLPA can determine the carrier status of SMA. The identification of three silent (2+0) carriers among the 44 parental samples indicated a risk for such families, for which genetic counseling and reproduction guidance should be provided.
Female ; Genetic Counseling ; Heterozygote ; Humans ; Multiplex Polymerase Chain Reaction ; Muscular Atrophy, Spinal/genetics* ; Pregnancy ; Prenatal Diagnosis ; Survival of Motor Neuron 1 Protein/genetics*

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.
China ; Female ; Genetic Carrier Screening ; Genetic Counseling ; Genetic Variation ; Heterozygote ; Humans ; Male ; Muscular Atrophy, Spinal ; genetics ; Pregnancy ; Prenatal Diagnosis ; Survival of Motor Neuron 1 Protein ; genetics ; Survival of Motor Neuron 2 Protein ; genetics

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.
Child ; Humans ; Muscular Atrophy, Spinal ; genetics ; Phenotype ; Survival of Motor Neuron 1 Protein ; genetics ; Survival of Motor Neuron 2 Protein ; genetics

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.
Adolescent ; Child ; Child, Preschool ; Female ; Humans ; Infant ; Infant, Newborn ; Male ; Muscular Atrophy, Spinal ; diagnosis ; genetics ; Mutation ; Sequence Analysis, DNA ; methods ; Survival of Motor Neuron 1 Protein ; genetics ; Survival of Motor Neuron 2 Protein ; genetics