Main findings
A total of 10 variation sequences of 7 genes were detected in these 14 cases, all of which were in heterozygous state, including 2 pathogenic variants, 4 likely pathogenic variants and 4 uncertain variants. Of the 14 cases, 4 cases were definitively diagnosed and classified as positive cases, with a definite diagnosis rate of 28.6% (n=4/14).Normand Ea. Et al. performed total exome sequencing on 146 prenatal samples, and molecular diagnosis was performed in 46 of them, with a diagnosis rate of 32%.8Fu M et al. performed total external sequencing on 19 abortive tissues, and a total of 36 variation sequences were detected, among which 12 were pathogenicity variants, with a diagnostic rate of 33%.9The diagnostic rates in this study are in line with those of 22-36% in previous large studies.5The four patients with positive results, including six variants, offered diagnoses including short rib dysplasia type 3, autosomal dominant polycystic kidney disease type 4, and Alagille syndrome. Among the positive cases, except case 2, which had autosomal dominant disease and the variation was from the mother, the remaining 3 cases had autosomal recessive disease and both parents were carriers of the genetic variation.
Alagille syndrome (ALGS) is an autosomal dominant inherited disease, which can be caused by a variety of mutations in JAG1 gene (including complete gene deletion, missense mutation, splice site mutation, senseless mutation, etc.),10 indicating that insufficient haploidy of JAG 1 gene can cause the pathogenic cause of ALGS clinical phenotype.11, 12JAG1 gene encodes the surface ligand JAG1 , which is a highly conserved Notch signaling pathway. 13, 14The ligand interacts with Notch receptor to regulate gene transcription and plays a key role in cell development and multi-organ system formation.10, 15, 16Case 2 reported that c.2078-2079delGT mutation of JAG1 gene was splicing mutation, which would lead to premature translation termination codon and function loss, resulting in insufficient haploidy of JAG1 gene, leading to clinical phenotypes related to Alagille syndrome. The main clinical features of ALGS include liver and heart disease, butterfly vertebrae, and specific facial features (triangular face, pointed chin). In addition to these features, most patients also have renal and vascular abnormalities.17-19 In the fetuses diagnosed with Alagille syndrome, there were obvious renal abnormalities and other sonographic phenotypes, which were consistent with the neonatal phenotype of ALGS
Cases 5 and 7:Two cases of sonographic features all have four short limbs which development, chest is narrow, and there are abnormal heart development, including 5 cases and refers to much and toe deformity, this is completely in line with short rib dysplasia type 3 typical sonographic features (shorten long bone, thoracic stenosis, occasionally means more, can also be involved in heart, liver, brain and other system exceptions).20Short-costal dysplasia type 3 is a common autosomal recessive osteochondrodysplasia disorder, and theDYNC2HI gene variant is associated with Short-costal dysplasia type 3 syndrome. 21The DYNC2H1 gene, located at 11q22.3, encodes the heavy chain of cytoplasmic dynamin 2, which is involved in flagella transport and affects chondrocyte maturation.22, 23 At the same time, DYNC2H1gene defect leads to the interruption of Hedgehog signaling pathway, thus affecting the proliferation and differentiation of osteoblasts and chondrocytes, leading to chondrodysplasia.24, 25
The whole exon sequencing results of Case 1 indicated that the patient was a repeated compound heterozygous variant of the PKHD1 gene C. 8301delC (p.Asn2768FS) and exon 57-60, which was associated with type 4 phenotype of autosomal recessive polycystic kidney disease. In addition, ultrasonography suggested that the fetal renal volume was increased, suggesting that the infant polycystic kidney was considered. In case 4, ultrasound showed abnormal development of thoracic vertebrae, cleft lip and palate, congenital abnormal development of heart: Tetralogy of Fallot, single umbilical artery. Whole exome sequencing detectedGLA gene and Nodal gene variation. Fabry disease caused byGLA gene c.61C>G heterozygous variation can cause heart, kidney and cerebrovascular diseases, while visceral ectopia caused by Nodal gene variation can lead to abnormal trunk development and severe congenital heart defect. The disease caused by this mutation can explain part of the clinical phenotype of the abortive tissue. Although it cannot be classified as a positive case, it can explain the related reasons of the abortive phenotype. Further functional analysis can be carried out to clarify the role of this mutation site.
Heterozygous variation of GJB2 gene c.176_191del (p.G59fs) was detected in the fetus of case 9. According to the laboratory classification standard, this mutation was identified as pathogenicity variation, which originated from the father. The pregnant woman in Case 10 had a history of two abortions, and the aborted tissue had not been tested for relevant genes before. In the whole exon sequencing of the flow product, the heterozygous mutation of F5 gene (c. 4964C>T) was found, which could lead to the related phenotypes of recurrent abortion susceptibility type 1 and factor V deficiency.