Analysis Of Bone Density And Its Influencing Factors In Children With Spinal Muscular Atroph

Part one:Bone mineral density in children with spinal muscular atrophy types 2 and 3Background:Sipnal muscular atrophy(SMA)is an autosomal recessive motor neuro disease,generally refers to the progressive degeneration of motor neurons caused by biallelic loss of function mutations of survival motor neuron 1(SMN1)gene on the long arm of chromosome 5(5q),which also known as 5q-SMA.Its incidence is about 1/11 000 birth and it is included in the first list of rare disease in China.SMA is the most common genetic disease of infant motality,the main clinical manifestations including muscle weakness and atrophy.Children of different ages can show different severity of illness.AS the disease progresses,patients are prone to bone complications.Bone mass and bone mineral density reduction lead to fractures,which directly interfere with the quality of life in SMA children.Therefore,it is of great significance to carry out bone mineral density monitoring clinically,and it can effectively reduce the risk of fracture according to the bone density level.The International Society for Clinical Density(ISCD)recommended dual-energy X-ray absorptiometry(DXA)as the "gold standard" for bone mineral density evaluation,and current research based on this standard is mostly targeted at European and American populations,and there is a lack of research on bone mineral density in children with SMA in China.Because bone mineral density is closely related to genetics and race,foreign data do not apply to China.Obtaining basic data on bone mineral density in children with SMA in China can provide important guidance for clinical bone health management.Objectives:Based on a prospective cross-sectional study of bone mineral density(BMD)in SMA types 2 and 3 patients of single-center in northern regions,the basic data of BMD in different SMA types were obtained,and the differences in BMD between patients with different phenotypes and genotypes were compared.Methods:1.Study subjects:This study included children aged 3-18 years with SMA types 2 and 3 who were genetically diagnosed(detect SMN1 and SMN2 copy numbers).We collected the clinical data and history,and divided the patients into 2a,2b,3a,and 3b four subtypes according to age at symptom onset and acquired motor milestones.2.Anthropometry:Mainly standing height measurements,the results were recorded in centimeter(cm).The height Z-score was calculated by reference to the normal Chinese children’ s standard.3.Fractures:Patients were asked for fracture history and completed frontal and lateral X-ray images of the entire spinal column.Radiographs were evaluated by two pediatric radiologists to diagnose compression fractures of the spine.4.Bone densitometry:DXA scanning was used to detect total body less head bone mineral density(TBLH BMD)and lumbar spine bone mineral density(LS BMD).The results were expressed as area mineral bone mineral density(aBMD)(g/cm2).The BMD Z-score was calculated by reference to the normal BMD data of Chinese children and adolescents in the same age and sex.The differences in BMD between children with different SMA types and different SMN2 copy numbers in children of SMA type 3 were compared,and Jonckheere-Terpstra test was used to analyze the trend of BMD among SMA 2a-3b subtypes.Results:1.A total of 40 patients met the inclusion criteria,19 males and 21 females,aged 3 to 17.4 years,the medium age was 5.5(4.3,8.7)years.In all,22 were SMA type 2(SMA 2a=11,SMA 2b= 11)and 18 SMA Type 3(SMA 3a=13,SMA 3b=5).The disease course was from 0.7 to 12.0 years at the time of recruited,and the medium disease course was 4.2(3.1,6.8)years.The numbers of SMN2 copies in all patients with SMA types 2 was 3,and among children with SMA type 3,12 cases were 3 copies and 6 cases were 4 copies.2.The mean height Z-score of all the patients in this study was 0.1±1.4,of which 5 patients(12.5%)met the criteria of short stature(height Z<-1).3.Medical history showed that 2 cases(5%)with low-traumatic long bone fractures,and none of the patients in the study had vertebral fractures.4.The mean TBLH BMD(g/cm2)of the 40 children in this group was 0.408±0.11,mean LS BMD(g/cm2)was 0.463±0.13.After calculating and correcting BMD Z-scores in children with short stature,the mean TBLH BMD Z-score of all patients was-3.0±1.8,mean LS BMD Z-score was-1.3±1.4.Based on the data of normal Chinese children and adolescents with the same age and sex,the mean TBLH BMD for SMA patients was below the 5th percentile of the normal population,and the mean LS BMD was between the 5th to 10th percentile.5.Among the 40 patients in this study,27 cases(67.5%)were diagnosed with low BMD,and 1 case(2.5%)was diagnosed with osteoporosis.The diagnosis rate of low BMD in children with SMA type 2 was significantly higher than that of type 3(86.4%vs.44.4%,p=0.008).The mean TBLH BMD Z-score and LS BMD Z-score were significantly lower in children with SMA type 2 than in type 3(-3.7±1.6 vs.-2.0±1.7,p=0.002;-1.9±1.2 vs.-0.6±1.4,p=0.002).Both TBLH BMD Z-scores and LS BMD Z-scores tended to increase significantly with the change of SMA subtypes from 2a-3b(p=0.001,p<0.001).In children with SMA type 3,the TBLH BMD Z-scores and LS BMD Z-scores were compared between groups who carried 3 and 4 SMN2 gene copy numbers,and the difference was not statistically significant(-2.3±1.7 vs.-1.5±1.6,p>0.05;-0.6±1.5 vs.-0.6±1.0,p>0.05).Conclusions:1.The BMD of SMA types 2 and 3 patients in this study decreased,the mean TBLH BMD was below the 5th percentile of the normal Chinese children and adolescents with same age and same sex,the mean LS BMD was in the 5th-10th percentile,and 70%of the patients could be diagnosed with low BMD or osteoporosis.2.There are differences between TBLH BMD and LS BMD in children with SMA subtypes 2a-3b,and the more severe the phenotype,the more obvious lower BMD.The effect of different SMN2 gene copy numbers on BMD in children with SMA type 3 was not significant.3.Regular BMD monitoring by DXA scanning in children with SMA types 2 and 3 is an important way to assess bone health objectively.Part two:The influencing factors of bone mineral density in children with spinal muscular atrophy types 2 and 3Background:Studies indicated that children’s BMD status could be regulated by a variety of factors,including some inherent factors such as genetics,ethnicity,sex,and some acquired factors such as nutrition,physical activity,hormone levels.Among them,heredity is the basic factor that determines BMD.Secondly,serum calcium,phosphorus,vitamin D,PTH and other bone metabolism markers,as well as muscle,fat and other body components act on bones through biological regulation and mechanical stimulation,and play a regulatory role in bone formation and absorption.Children with SMA are prone to appear low BMD or osteoporosis,which is a high-risk factor of low-trauma fracture.Effective bone health management aimed at these factors is an important part of SMA therapy.However,there is still a lack of systematic research on the influencing factors of BMD in Chinese SMA patients.Finding the main relevant factors of BMD in SMA children is an urgent problem to be solved,which is conducive to raise the level of bone health management in SMA patients.Objectives:To explore the main influencing factors of BMD in SMA types 2 and 3 patients in a single medical center,by summary of clinical data combined with laboratory test indicators and body composition analysis.Methods:1.Study subjects:See part one of this study.2.Anthropometry:Weight and height were measured,and body mass index(BMI)was calculated according to the formula,and BMI Z-scores were calculated with reference to the standard of normal children and adolescents in China.3.Laboratory analyses:Tested serum bone metabolism markers in enrolled children with SMA types 2 and 3,including serum calcium(Ca),Phosphorus(P),alkaline phosphatase(ALP),25-OH-D concentration,parathyroid hormone(PTH)levels and compared them separately among children with SMA 2a-3b subtypes.4.DXA Scans:The appendicular skeletal muscle mass(ASM),fat mass percentage(FMP)and body mass(Total Mass,TM)were obtained for enrolled patients by DXA Scanning,and the appendicular skeletal muscle mass weight ratio(ASMR)Z-scores and FMP Z-scores were calculated according to the normal standards of children and adolescents in China.Summarized the changes in body composition and compared the differences among children with different subtypes of SMA.5.Screened potential factors influencing TBLH BMD and LS BMD based on the outcomes of Bivariate correlations in these patients.A multivariate linear regression model was established,the TBLH BMD Z-scores and LS BMD Z-scores were used as dependents,and the potential factors screened out were included as independents into the regression equation for statistical analysis.Results:1.Total 40 patients,19 males and 21 females,aged 3 years to 17.4 years.In all,22 were SMA type 2(SMA 2a=11,SMA 2b=11)and 18 SMA Type 3(SMA 3a= 13,SMA 3b=5).No patients had used vitamin D and calcium supplements regularly in the previous 3 months.2.The serum 25-OH-D level fulfilled the criteria for insufficiency(37.550.0 nmol/L)in 6 children(15%),deficiency(≤37.5 nmol/L)in 9 children(22.5%),and there was no severe deficiency.Comparing among SMA 2a-3b subtypes,no statistically significant differences in serum bone metabolism markers were observed(P>0.05).There was a significant negative correlation between serum 25-OH-D concentrations and PTH levels(r=-0.536,p<0.001).There were no significant abnormalities in serum Ca,P,ALP,and PTH levels in all enrolled children.3.The mean BMI Z-score in 40 patients was-0.4±2.2.BMI Z-scores were compared between the four subtypes of SMA 2a-3b,and the difference was notstatistically significant(p>0.05).DXA body composition measurements were performed in all 40 patients.The mean ASMR Z-score was-3.2±1.2(-2.0<Z<2.0),the mean FMP Z-score was 1.8±1.4(-2.0<Z<2.0),and FMP Z-scores>2.0 in 16 children(40%)which showed increasing.We can observe a significant upward trend of SMA 2a-3b four subtypes with ASMR Z-scores(p=0.007)and there was no significant difference among the four subtypes with FMP Z-scores(p>0.05).There was a significant negative correlation between the ASMR Z-scores and the FMP Z-scores(r=-0.723,p<0.001).4.Four items including serum PTH level,BMI Z-score,disease course,and subtype were screened out as potential BMD influencing factors for inclusion in the multiple linear regression model.The results showed that both subtype and BMI Z-scores were significantly positive correlated with TBLH BMD Z-scores β=0.680,95%CI 0.324～1.037,p<0.001;β=0.484,95%CI 0.323～0.645,p<0.001),and the disease course was significantly negative correlated with TBLH BMD Z-scores(β=-0.161,95%CI-0.285～-0.037,p=0.012).Subtype and BMI Z-scores were significantly positive correlated with LS BMD Z-scores(β=0.790,95%CI 0.421～1.158,p<0.001;β=0.240,95%CI 0.073～0.406,p=0.006).Conclusions:1.Subtype,BMI,and disease course were the main influencing factors of BMD in children with SMA types 2 and 3 in our study.The heavier the phenotype and the smaller the BMI,the more obvious reduction of TBLH BMD and LS BMD.The longer the course of the disease,the more pronounced reduction in TBLH BMD.Therefore,we should pay more attention to the BMD status in SMA patients with low BMI,long disease course and severer phenotype and intervene as early as possible to improve prognosis.2.Vitamin D deficiency or deficiency occured in more than 1/3 of these patients.We recommend regular monitoring and timely supplementation.