Genetic analysis and preimplantation genetic diagnosis of Chinese Marfan syndrome patients

Reassessment of FBN1 variants of uncertain significance using updated ClinGen guidance for PP1/BS4 and PP4 criteria

Marfan syndrome (MFS) is a genetic disorder caused by an FBN1 variant and is diagnosed based on the revised Ghent criteria, which incorporate clinical manifestations and genetic testing. Up-to-date FBN1 variant interpretation is crucial for proper diagnosis and management of MFS; however, some FBN1 variants of uncertain significance (VUSs) remain inconclusive despite applying Clinical Genome Resource (ClinGen) FBN1-specific guideline. Recently, the ClinGen guidance for PP1/BS4 co-segregation and PP4 phenotype specificity criteria (new PP1/PP4 criteria) were released. Here, we performed reassessment of FBN1 VUSs using these new PP1/PP4 criteria. FBN1 VUSs collected from December 2015 to April 2024 were reassessed according to the ClinGen FBN1-specific guideline and new PP1/PP4 criteria. Medical records and previous studies were reviewed to evaluate the phenotype-specificity of evidence based on the revised Ghent criteria. Collectively, 927 patients with suspected MFS underwent FBN1 sequencing and 72 VUSs were detected. When applying the FBN1-specific guideline only, of 72 VUSs, 29 (40.3%) were reclassified as pathogenic variants (PVs) or likely PVs (LPVs). When additionally applying the new PP1/PP4 criteria, 16 (37.2%) of the remaining 43 VUSs were reclassified as LPVs. After reassessing FBN1 VUSs according to the new PP1/PP4 criteria, the rate of reclassification from VUS to PV/LPV significantly increased from 40.3% to 62.5%. The new PP1/PP4 criteria provide sufficient evidence for evaluating the pathogenicity of FBN1 variants detected in MFS patients fulfilling the revised Ghent criteria and will be helpful in clinical analysis.

Identification of two variants in PAX3 and FBN1 in a Chinese family with Waardenburg and Marfan syndrome via whole exome sequencing

Both Warrensburg (WS) and Marfan syndrome (MFS) can impair the vision. Here, we recruited a Chinese family consisting of two WS affected individuals (II:1 and III:3) and five MFS affected individuals( I:1, II:2, III:1, III:2, and III:5) as well as one suspected MFS individual (II:4). Using whole exome sequencing (WES) and subsequent PCR-Sanger sequencing, we identified one novel heterozygous variant NM_000438 (PAX3) c.208 T > C, (p.Cys70Arg) from individuals with WS and one previous reported variant NM_000138 (FBN1) c.2740 T > A, (p.Cys914Ser) from individuals with MFS and co-segregated with the diseases. Real-time PCR and Western blot assay showed that, compared to their wild-type, both mRNAs and proteins of  PAX3 and FBN1 mutants reduced in HKE293T cells. Together, our study identified two disease-causing variants in a same Chinese family with WS and MFS, and confirmed their damaged effects on their genes' expression. Therefore, those findings expand the mutation spectrum of PAX3 and provide a new perspective for the potential therapy.

Advances in Genetic Diagnosis of Kallmann Syndrome and Genetic Interruption

Kallmann syndrome (KS) is a rare hereditary disease with high phenotypic and genetic heterogeneity. Congenital hypogonadotropic hypogonadism and hyposmia/anosmia are the two major characterized phenotypes of KS. Besides, mirror movements, dental agenesis, digital bone abnormalities, unilateral renal agenesis, midline facial defects, hearing loss, and eye movement abnormalities can also be observed in KS patients. Because of the phenotypic heterogeneity, genetic diagnosis become increasingly valuable to distinguish KS from other disorders including normosmic congenital hypogonadotropic hypogonadism, constitutional delay of growth and puberty, CHARGE syndrome, and functional hypogonadotropic hypogonadism. Application of next-generation sequencing has promoted the discovery of novel pathogenic genes in KS pedigrees. Prenatal diagnosis is an effective method in clinical settings to decrease birth defects and block transmission of genetic disorders. However, pregnant women may suffer from physical and psychological distress when fetuses are diagnosed with congenital defects. Preimplantation genetic testing (PGT) is a prospective approach during the in vitro fertilization process that helps to interrupt transmission of hereditary diseases to offspring at an early stage. Thus, genetic testing and counseling are recommended to KS patients with family histories, prenatal diagnosis and PGT are considered to be useful options.

Preimplantation genetic testing for a family with usher syndrome through targeted sequencing and haplotype analysis

Background

Preimplantation genetic testing for monogenic defects (PGT-M) has been available in clinical practice. This study aimed to validate the applicability of targeted capture sequencing in developing personalized PGT-M assay.

Methods

One couple at risk of transmitting Usher Syndrome to their offspring was recruited to this study. Customized capture probe targeted at USH2A gene and 350 kb flanking region were designed for PGT-M. Eleven blastocysts were biopsied and amplified by using multiple displacement amplification (MDA) and capture sequencing. A hidden Markov model (HMM) assisted haplotype analysis was performed to deduce embryo’s genotype by using single nucleotide polymorphisms (SNPs) identified in each sample. The embryo without paternal rare variant was implanted and validated by conventional prenatal or postnatal diagnostic means.

Results

Four embryos were diagnosed as free of father’s rare variant, two were transferred and one achieved a successful pregnancy. The fetal genotype was confirmed by Sanger sequencing of fetal genomic DNA obtained by amniocentesis. The PGT-M and prenatal diagnosis results were further confirmed by the molecular diagnosis of the baby’s genomic DNA sample. The auditory test showed that the hearing was normal.

Conclusions

Targeted capture sequencing is an effective and convenient strategy to develop customized PGT-M assay.