Exome Sequencing Identified a Novel FBN2 Mutation in a Chinese Family with Congenital Contractural Arachnodactyly

Identification of Six Pathogenic Genes for Tibetan Familial Ventricular Septal Defect by Whole Exome Sequencing

INTRODUCTION

Ventricular septal defect (VSD) is the most common congenital heart malformation in children. This study aimed to investigate potential pathogenic genes associated with Tibetan familial VSD.

METHODS

Whole genomic DNA was extracted from eight Tibetan children with VSD and their healthy parents (a total of 16 individuals). Whole-exome sequencing was performed using the Illumina HiSeq platform. After filtration, detection, and annotation, single nucleotide variations and insertion-deletion markers were examined. Comparative evaluations using the Sorting Intolerant from Tolerant, PolyPhen V2, Mutation Taster, and Combined Annotation Dependent Depletion databases were conducted to predict harmful mutant genes associated with the etiology of Tibetan familial VSD.

RESULTS

A total of six missense mutations in genetic disease-causing genes associated with the development of Tibetan familial VSD were identified: activin A receptor type II-like 1 (c.652 C > T: p.R218 W), ATPase cation transporting 13A2 (c.1363 C > T: p.R455 W), endoplasmic reticulum aminopeptidase 1 (c.481 G > A: p.G161 R), MRI1 (c.629 G > A: p.R210Q), tumor necrosis factor receptor-associated protein 1 (c.224 G > A: p.R75H), and FBN2 (c.2260 G > A: p.G754S). The Human Gene Mutation Database confirmed activin A receptor type II-like 1, MRI1, and tumor necrosis factor receptor-associated protein 1 as pathogenic mutations, while FBN2 was classified as a probable pathogenic mutation.

CONCLUSIONS

This novel study directly screens genetic variations associated with Tibetan familial VSD using whole-exome sequencing, providing new insights into the pathogenesis of VSD.

Identification of a HOXD13 variant in a Mongolian family with incomplete penetrance syndactyly by exon sequencing

Background

Syndactyly (SD) refers to a deformity caused by the fusion and limb differentiation disorder of soft tissues and/or skeletons to varying extents between adjacent fingers (toes). The main features of this disease are phenotypic heterogeneity and genetic heterogeneity. In this study, we examined four generations of a Chinese Mongolian with different phenotypes of syndactylia and analysed and identified the pathogenic genetic variants of SD by exon sequencing.

Methods

The clinical phenotypes of patients were analysed, and the hands and feet were examined by X-ray. The pedigree was drawn, and the family data were analysed. Peripheral blood was collected from the family members, and genomic DNA was extracted. The candidate genes of SD were identified by exon sequencing, and the mutation sites of the captured candidate genes were amplified by PCR and verified by Sanger sequencing.

Results

The family has congenital syndactyly, which is an autosomal dominant disease. At present, this condition has been passed down for 4 generations and was identified in 9 patients, including 4 males and 5 females. Five patients, I₂, II₄, III₅, III_,7 and III₁₀, had unilateral syndactyly, and four patients, III₁₆, IV₃, IV₆ and IV₇, had bilateral finger syndactyly. All of their toes were unaffected. The proband and the other patients in this family had a c.917G > A (p.R306Q) mutation, which is located at position 917 of the second exon of the HOXD13 gene. This mutation results in a change in the amino acid at position 306, in which arginine is changed to glutamine. This mutation cosegregates in unaffected individuals and affected patients in this family. Moreover, 201 Mongolian genome databases and a thousand human genome databases were referenced to further confirm that the pathogenic genetic variant that causes syndactyly in this family is found in HOXD13.

Conclusion

This study found that the mutation site of the pathogenic gene in this family was HOXD13, c.917G > A (p.R306Q). The phenotype of the family member III₁₂ was normal, but this member was also a carrier of the pathogenic genetic variant. This indicates that the disease of this family has incomplete penetrance characteristics. Our results further enrich the expression profile of the HOXD13 gene.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01360-3.

Mutation analysis and prenatal diagnosis of a family with congenital contractural arachnodactyly

BACKGROUND

Congenital contractural arachnodactyly (CCA) is a rare autosomal dominant condition caused by mutations in the fibrillin 2 gene (FBN2). The primary clinical symptoms of CCA include multiple flexion contractures, arachnodactyly, dolichostenomelia, scoliosis, abnormal pinnae, muscular hypoplasia, and crumpled ears.

METHODS

We used whole-exome sequencing technology to examine an arthrogryposis multiplex congenita and used Sanger sequencing technology to genetically confirm its family.

RESULTS

FBN2 c.3344A>T(p.D1115V) was identified in this family with CCA in a pedigree. Prenatal diagnosis and counseling were carried out simultaneously to avoid the birth of the sick fetus.

CONCLUSION

The study is on FBN2 variant in CCA, which potentially having implications for genetic counseling and clinical management, our study may provide new insights into the cause and diagnosis of CCA.

Double heterozygous variants in FBN1 and FBN2 in a Thai woman with Marfan and Beals syndromes

A phenotype of an individual is resulted from an interaction among variants in several genes. Advanced molecular technologies allow us to identify more patients with mutations in more than one genes. Here, we studied a Thai woman with combined clinical features of Marfan (MFS) and Beals (BS) syndromes including frontal bossing, enophthalmos, myopia, the crumpled appearance to the top of the pinnae, midface hypoplasia, high arched palate, dermal stretch marks, aortic enlargement, mitral valve prolapse and regurgitation, aortic root dilatation, and progressive scoliosis. The aortic root enlargement was progressive to a diameter of 7.2 cm requiring an aortic root replacement at the age of 8 years. At her last visit when she was 19 years old, she had moderate aortic regurgitation. Exome sequencing revealed that she carried the c.3159C > G (p.Cys1053Trp) in exon 26 of FBN1 and c.2638G > A (p. Gly880Ser) in exon 20 of FBN2. The variant in FBN1 was de novo, while that in FBN2 was inherited from her unaffected mother. Both genes encode for fibrillins, which are essential for elastic fibers and can form the heterotypic microfibrils. Two defective fibrillins may synergistically worsen cardiovascular manifestations seen in our patient. In this study, we identified the fourth patient with both MFS and BS, carrying mutations in both FBN1 and FBN2.

A Novel Splicing Mutation in the FBN2 Gene in a Family With Congenital Contractural Arachnodactyly

Congenital contractural arachnodactyly (CCA) is an extremely rare monogenic disorder in humans, and the prevalence of CCA is estimated to be less than 1 in 10,000 worldwide. CCA is characterized by arachnodactyly, camptodactyly, the contracture of major joints, scoliosis, pectus deformities, and crumpled ears. Mutations in FBN2 (which encodes fibrillin-2) are responsible for causing this disease. A family with CCA was investigated in this study, and a novel variant, c.3724+3A > C (also identified as IVS28+3A > C), in FBN2 was found in nine patients from the family but was not found in seven unaffected relatives. Reverse transcription-PCR (RT-PCR) and complementary DNA (cDNA) sequencing data showed that exon 28 was skipped in the FBN2 gene. The FBN2 c.3724+3A > C variant led to an in-frame deletion during transcription, which eventually triggered CCA in the Chinese family.

A novel FBN2 mutation cosegregates with congenital contractural arachnodactyly in a five-generation Chinese family

We identified a novel heterozygous mutation (c.4177T>G and p.Cys1393Gly) in FBN2 that cosegregated with congenital contractural arachnodactyly (CCA) in a five-generation Chinese family. This mutation may cause the loss of the disulfide bond between Cys 1393 and Cys 1378 residues of fibrillin-2. Our study expands the genetic profile of CCA.