Genetic Bases of Bicuspid Aortic Valve: The Contribution of Traditional and High-Throughput Sequencing Approaches on Research and Diagnosis

Bicuspid aortic valve (BAV) is a common (0.5-2.0% of general population) congenital heart defect with increased prevalence of aortic dilatation and dissection. BAV has an autosomal dominant inheritance with reduced penetrance and variable expressivity. BAV has been described as an isolated trait or associated with syndromic conditions [e.g., Marfan Marfan syndrome or Loeys-Dietz syndrome (MFS, LDS)]. Identification of a syndromic condition in a BAV patient is clinically relevant to personalize aortic surgery indication. A 4-fold increase in BAV prevalence in a large cohort of unrelated MFS patients with respect to general population was reported, as well as in LDS patients (8-fold). It is also known that BAV is more frequent in patients with thoracic aortic aneurysm (TAA) related to mutations in ACTA2, FBN1, and TGFBR2 genes. Moreover, in 8 patients with BAV and thoracic aortic dilation, not fulfilling the clinical criteria for MFS, FBN1 mutations in 2/8 patients were identified suggesting that FBN1 or other genes involved in syndromic conditions correlated to aortopathy could be involved in BAV. Beyond loci associated to syndromic disorders, studies in humans and animal models evidenced/suggested the role of further genes in non-syndromic BAV. The transcriptional regulator NOTCH1 has been associated with the development and acceleration of calcium deposition. Genome wide marker-based linkage analysis demonstrated a linkage of BAV to loci on chromosomes 18, 5, and 13q. Recently, a role for GATA4/5 in aortic valve morphogenesis and endocardial cell differentiation has been reported. BAV has also been associated with a reduced UFD1L gene expression or involvement of a locus containing AXIN1/PDIA2. Much remains to be understood about the genetics of BAV. In the last years, high-throughput sequencing technologies, allowing the analysis of large number of genes or entire exomes or genomes, progressively became available. The latter issue together with the development of "BigData" analysis methods improving their interpretation and integration with clinical data represents a promising opportunity to increase the disease knowledge and diagnosis in monogenic and multifactorial complex traits. This review summarized the main knowledge on the BAV genetic bases, the role of genetic diagnosis in BAV patient managements and the crucial challenges for the comprehension of genetics of BAV in research and diagnosis.

Characteristic and influencing factors of Taqman genotyping calling error

BACKGROUND

Taqman fluorescent probe was frequently applied in single nucleotide polymorphism (SNP) genotyping. However, the characteristic of calling error and the influencing factors remain unclear.

METHOD

Calling errors of Taqman genotyping was evaluated systematically based on Mendelian inheritance. Twenty-two SNPs were genotyped by Taqman probe for 419 pedigrees. Mendelian genetic errors were counted for every SNP and pedigree. Cluster analysis was applied to investigate the compatibility between Taqman probes and DNA sample.

RESULTS

On one hand, errors were found for all the SNPs. The error number ranged from 4 to 33 with median of 10.5. On the other hand, Mendelian genetic errors showed features of both randomness and cluster. Half of the pedigrees containing errors had only 1 Mendelian genetic error. But there was also a pedigree containing up to 10 Mendelian genetic errors. Furthermore, cluster analysis indicated that errors of different SNPs took place in different pedigree cluster.

CONCLUSION

It could be concluded that calling error is inevitable for Taqman genotyping of large samples. The quality of Taqman probe and DNA sample, as well as their compatibility, may account for the error incidence.

Malformations among 289,365 Births Attributed to Mutations with Autosomal Dominant and Recessive and X-Linked Inheritance

BACKGROUND

The number of malformations attributed to mutations with autosomal or X-linked patterns of inheritance has increased steadily since the cataloging began in the 1960s. These diagnoses have been based primarily on the pattern of phenotypic features among close relatives. A malformations surveillance program conducted in consecutive pregnancies can identify both known and "new" hereditary disorders.

METHODS

The Active Malformations Surveillance Program was carried out among 289,365 births over 41 years (1972-2012) at Brigham and Women's Hospital in Boston. The findings recorded by examining pediatricians and all consultants were reviewed by study clinicians to establish the most likely diagnoses. The findings in laboratory testing in the newborn period were reviewed, as well.

RESULTS

One hundred ninety-six (0.06%) infants among 289,365 births had a malformation or malformation syndrome that was attributed to Mendelian inheritance. A total of 133 (68%) of the hereditary malformations were attributed to autosomal dominant inheritance, with 94 (71%) attributed to apparent spontaneous mutations. Forty-six (23%) were attributed to mutations with autosomal recessive inheritance, 17 associated with consanguinity. Seventeen (9%) were attributed to X-linked inheritance. Fifteen novel familial phenotypes were identified. The family histories showed that most (53 to 71%) of the affected infants were born, as a surprise, to healthy, unaffected parents.

CONCLUSION

It is important for clinicians to discuss with surprised healthy parents how they can have an infant with an hereditary condition. Future studies, using DNA samples from consecutive populations of infants with malformations and whole genome sequencing, will identify many more mutations in loci associated with mendelizing phenotypes. Birth Defects Research 110:92-97, 2018.© 2018 Wiley Periodicals, Inc.

Mendelian genetics

The author reviews the inheritance patterns of diseases or conditions caused by genes at a single locus. The recurrence risk in several common family situations is illustrated for autosomal recessive, autosomal dominant, and X-linked inheritance. Patients frequently have difficulty understanding these concepts, and a few examples are provided of problems encountered in genetic counselling.