| BackgroundFetal skeletal dysplasia is a common birth defect during pregnancy which the incidence rate during pregnancy is 1/1300-1/1350.There are many types of fetal skeletal dysplasia.According to different prognosis,they are roughly divided into two categories:fatal skeletal dysplasia and non-fatal skeletal dysplasia.Fatal skeletal dysplasia often causes lung hypoplasia,leading to neonatal or perinatal death;while non-fatal skeletal dysplasia can survive,but most of the treatment effects are unstable,which performing functional or appearance defects seriously affecting the quality of life,so accurate prenatal diagnosis classification can provide the family with correct genetic counseling suggestions and reasonable clinical decision-making basis which avoiding the birth of fatal and severely disabled children and improving the quality of the birth population.The prenatal diagnosis methods for fetal skeletal dysplasia mainly include ultrasound screening and genetic examination.Ultrasound screening is the most commonly used and most important first-line screening method.However,due to the genetic heterogeneity and phenotypic overlap of skeletal dysplasia,sonographers can only judge fatal skeletal dysplasia through some ultrasound indicators.The accuracy rate is up to 92-96%,but there are still less than 8%of fetal prenatal ultrasound diagnosis errors resulting in wrong consultation and clinical treatment decisions.At present,genetic testing methods include chromosome karyotype analysis,chromosome microarray analysis,Sanger sequencing,skeletal dysplasia Panel,whole-exome sequencing.The routine clinical testing strategies are chromosome karyotype analysis,chromosome microarray analysis,hot spot mutation rapid screening,Panel,and whole-exome sequencing technology are screened in sequence,but this detection strategy has a long diagnosis cycle and high cost.Most fetuses are already in the third trimester when they are diagnosed,which is a decision-making belt for clinicians.It is a great challenge,and the termination of pregnancy at the late stage also brings heavy psychological and physical trauma to pregnant women.Because the whole-exome sequencing technology can simultaneously detect chromosome abnormalities and gene mutations and other genetic causes,the detection rate is high,and the economy is fast.Therefore,this study tried to use prenatal ultrasound combined with whole-exome sequencing technology to explore its genetic causes,providing a basis for family diagnosis,genetic counseling and follow-up prenatal diagnosis.At the same time,we explore the relationship between genotype and phenotype by analyzing the ultrasound phenotype to improve the diagnostic accuracy of prenatal ultrasound.Purpose1.In this study,61 pedigrees of fetal skeletal dysplasia were indicated by prenatal ultrasound,and the whole exome sequencing technology was used to explore the genetic etiology;2.Explore the common phenotypes of fetal skeletal dysplasia and their relationship between genotypes and ultrasonic phenotype.3.Establish a prenatal diagnosis system for hereditary skeletal dysplasia.Method1.Whole Exome SequencingUsing whole-exome sequencing to detect the genetic causes of 61 pedigrees with abnormal fetal skeletal dysplasia,verified by Sanger sequencing of the suspected mutations,and analyzing common pathogenic genes and variants of fetal skeletal dysplasia.2.Ultrasound screeningThe continuous sequential ultrasound system screening method was used to evaluate the ultrasound phenotypes of 34 fetal skeletal dysplasia,and analyze the common phenotypes of fetal skeletal dysplasia and the relationship between genotypes and ultrasound phenotypes.3.Invasive prenatal diagnosisObtain prenatal specimens of 49 pedigrees of hereditary skeletal dysplasia by transabdominal ultrasound-guided chorionic biopsy or amniocentesis.Based on the results of the probands genetic diagnosis,Sanger sequencing,MLPA,chromosome microarray analysis are used for different pedigrees for prenatal genetic testing.Result1.Results of genetic diagnosis of fetal skeletal dysplasiaAmong the 61 pedigrees,50pedigrees have confirmed the genetic etiology through whole-exome sequencing,with an abnormality rate of 81.97%;the genes involved are FGFR3,COL1A1,COL1A2,COL2A1,DYNC2H1,ALPL,EVC2,NPR2,RMRP,RUNX2,ASXL2and TRPV4.The most common variant genes are FGFR3,COL1A1,COL1A2,DYNC2H1,and ALPL.A total of 48 variants were detected,including 21 known pathogenic variants and 27 novel variants.These variants involved 5 variant types,including missense variants,nonsense variants,frameshift variants,and whole code variants.Missense mutations are the most common.There are obvious hot spots in FGFR3 gene mutations.FGFR3 genes c.1138G>A and c.742C>T lead to achondroplasia and lethal dwarf,respectively;COL1A1 and COL1A2 are the most common in osteogenesis imperfecta,and mainly missenses.Mutations are the main ones,and the amino acid changes are mainly the glycine changes in the Gly-XY unit.2.Prenatal ultrasound phenotype analysis of abnormal fetal skeletal developmentThe most common phenotype of abnormal fetal bone development is short limb deformity.Among them,FL/AC is less than 0.16 or FL lags behind the same gestational week for normal fetuses with 8SD or more,narrow thorax,and poor overall ossification are important indicators for predicting fatal skeletal dysplasia;osteogenesis imperfecta Ⅱ and Ⅲ are more often fractures of long bones in the fetus.The main manifestations of perinatal fatal hypophosphatase ultrasound are short limbs,long bones bent into angles,and poor ossification of the whole body,especially with the absence of vertebral ossification centers which is different from other types of skeletal dysplasia.3.Prenatal diagnosis results of 49 cases of skeletal disease familiesOne fetuse was detected by chromosome microarray analysis with 10q duplication,four fetuses were detected by MLPA with large deletions of dominant genes,and 13 fetuses were confirmed by Sanger sequencing to carry the same genetic mutation as the proband.18 fetuses were diagnosed with hereditary bone disease consistent with the proband.After genetic counseling,the family chose to terminate the pregnancy.The results of the fetal abortion tissue gene test were consistent with the results of the prenatal diagnosis.31 normal and carrier fetuses continued to be pregnant,all of them were born,and no corresponding bone disease phenotypes were seen.Conclusion1.Whole exome sequencing technology has important application value in the prenatal diagnosis of fetal skeletal system diseases.It is an important supplement to prenatal ultrasound in the prenatal diagnosis of early pregnancy and rare skeletal abnormalities.27 novel mutations enrich the human gene mutation database.A case of a triploid child with skeletal abnormalities as the main manifestation was found on prenatal ultrasound.2.Prenatal ultrasound plays an irreplaceable role in the prenatal diagnosis of fetal skeletal dysplasia.It can roughly judge fatal skeletal dysplasia,but it is still unable to achieve accurate typing,and genetic testing is still needed to make accurate typing;3.Invasive prenatal diagnosis is an important prenatal diagnosis method that is clinically relatively safe,accurate and reliable to avoid the birth of children with bone diseases. |
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