Molecular Characterization of a Rare Case of Monozygotic Dichorionic Diamniotic Twin Pregnancy after Single Blastocyst Transfer in Preimplantation Genetic Testing (PGT).

Preimplantation genetic testing (PGT) is widely used to select unaffected embryos, increasing the odds of having a healthy baby. During the last few decades, it was accepted that monozygotic dichorionic diamniotic twin pregnancies occurred from the embryo splitting before Day 3 postfertilization according to Corner's dogma. Hence, the occurrence of a dichorionic diamniotic twin pregnancy after a single blastocyst transfer was considered a dizygotic pregnancy resulting from blastocyst transfer and concurrent natural fertilization. In our study, we have provided for the first time molecular proof that a single blastocyst transfer can result in a monozygotic dichorionic diamniotic twin pregnancy, invalidating Corner's dogma. In this case, we recommend systematically assessing the genetic status of dichorionic twins after single blastocyst transfer using prenatal diagnosis to exclude the risk from a potential concurrent spontaneous pregnancy and to ensure that both fetuses are unaffected. To achieve this goal, we have developed here an innovative noninvasive prenatal diagnosis by exclusion of paternal variants with droplet digital PCR, maximizing the reliability of genetic diagnosis. Further multicentric prospective studies using genetic testing are now required to establish the rate of blastocyst splitting leading to dichorionic pregnancy in PGT and to identify the risk factors.

Euthymic and depressed bipolar patients are characterized by different RNA editing patterns in blood.

Bipolar disorder (BD) is a worldwide leading cause of disability. Inflammation roles in this disease is well established. ADAR1-mediated RNA editing is one of the key mechanisms regulating the inflammatory response. We have identified a panel of RNA editing-based blood biomarkers which allowed to discriminate unipolar from BD depression with high accuracy. We confirmed here the diagnostic value of this panel in a new cohort of BD patients recruited in Brazil. We also identified new combinations which allow a clear discrimination of BD from healthy controls and among BD subgroups, confirming that RNA editing is a key mechanism in BD.

A game changer for bipolar disorder diagnosis using RNA editing-based biomarkers.

In clinical practice, differentiating Bipolar Disorder (BD) from unipolar depression is a challenge due to the depressive symptoms, which are the core presentations of both disorders. This misdiagnosis during depressive episodes results in a delay in proper treatment and a poor management of their condition. In a first step, using A-to-I RNA editome analysis, we discovered 646 variants (366 genes) differentially edited between depressed patients and healthy volunteers in a discovery cohort of 57 participants. After using stringent criteria and biological pathway analysis, candidate biomarkers from 8 genes were singled out and tested in a validation cohort of 410 participants. Combining the selected biomarkers with a machine learning approach achieved to discriminate depressed patients (n = 267) versus controls (n = 143) with an AUC of 0.930 (CI 95% [0.879-0.982]), a sensitivity of 84.0% and a specificity of 87.1%. In a second step by selecting among the depressed patients those with unipolar depression (n = 160) or BD (n = 95), we identified a combination of 6 biomarkers which allowed a differential diagnosis of bipolar disorder with an AUC of 0.935 and high specificity (Sp = 84.6%) and sensitivity (Se = 90.9%). The association of RNA editing variants modifications with depression subtypes and the use of artificial intelligence allowed developing a new tool to identify, among depressed patients, those suffering from BD. This test will help to reduce the misdiagnosis delay of bipolar patients, leading to an earlier implementation of a proper treatment.

Phosphodiesterase 8A to discriminate in blood samples depressed patients and suicide attempters from healthy controls based on A-to-I RNA editing modifications.

Mental health issues, including major depressive disorder, which can lead to suicidal behavior, are considered by the World Health Organization as a major threat to global health. Alterations in neurotransmitter signaling, e.g., serotonin and glutamate, or inflammatory response have been linked to both MDD and suicide. Phosphodiesterase 8A (PDE8A) gene expression is significantly decreased in the temporal cortex of major depressive disorder (MDD) patients. PDE8A specifically hydrolyzes adenosine 3',5'-cyclic monophosphate (cAMP), which is a key second messenger involved in inflammation, cognition, and chronic antidepressant treatment. Moreover, alterations of RNA editing in PDE8A mRNA has been described in the brain of depressed suicide decedents. Here, we investigated PDE8A A-to-I RNA editing-related modifications in whole blood of depressed patients and suicide attempters compared to age-matched and sex-matched healthy controls. We report significant alterations of RNA editing of PDE8A in the blood of depressed patients and suicide attempters with major depression, for which the suicide attempt took place during the last month before sample collection. The reported RNA editing modifications in whole blood were similar to the changes observed in the brain of suicide decedents. Furthermore, analysis and combinations of different edited isoforms allowed us to discriminate between suicide attempters and control groups. Altogether, our results identify PDE8A as an immune response-related marker whose RNA editing modifications translate from brain to blood, suggesting that monitoring RNA editing in PDE8A in blood samples could help to evaluate depressive state and suicide risk.

Ex vivo splicing assays of mutations at noncanonical positions of splice sites in USHER genes.

Molecular diagnosis in Usher syndrome type 1 and 2 patients led to the identification of 21 sequence variations located in noncanonical positions of splice sites in MYO7A, CDH23, USH1C, and USH2A genes. To establish experimentally the splicing pattern of these substitutions, whose impact on splicing is not always predictable by available softwares, ex vivo splicing assays were performed. The branch-point mapping strategy was also used to investigate further a putative branch-point mutation in USH2A intron 43. Aberrant splicing was demonstrated for 16 of the 21 (76.2%) tested sequence variations. The mutations resulted more frequently in activation of a nearby cryptic splice site or use of a de novo splice site than exon skipping (37.5%). This study allowed the reclassification as splicing mutations of one silent (c.7872G>A (p.Glu2624Glu) in CDH23) and four missense mutations (c.2993G>A (p.Arg998Lys) in USH2A, c.592G>A (p.Ala198Thr), c.3503G>C [p.Arg1168Pro], c.5944G>A (p.Gly1982Arg) in MYO7A), whereas it provided clues about a role in structure/function in four other cases: c.802G>A (p.Gly268Arg), c.653T>A (p.Val218Glu) (USH2A), and c.397C>T (p.His133Tyr), c.3502C>T (p.Arg1168Trp) (MYO7A). Our data provide insights into the contribution of splicing mutations in Usher genes and illustrate the need to define accurately their splicing outcome for diagnostic purposes.

Sequence contexts that determine the pathogenicity of base substitutions at position +3 of donor splice-sites.

Variations at position +3 of 5' splice-sites (5'ss) are reported to induce aberrant splicing in some cases but not in others suggesting that the overall nucleotidic environment can dictate the extent to which 5'ss are correctly selected. Functional studies of three variations identified in donor splice-sites of USH2A and PCDH15 genes sustain this assumption. To gain insights into this question, we compared the nucleotidic context of U2-dependent 5'ss naturally deviated (+3G,+3C, or+3T) from the+3A consensus with 5'ss for which a +3 variation (A>G, A>C, or A>T) was shown to induce aberrant splicing. Statistical differences were found between the two datasets, highlighting the role of one peculiar position in each context (+3G/+4A; +3C/-1G; and +3T/-1G). We provided experimental support to the biostatistical results through the analysis of a series of artificial mutants in reporter minigenes. Moreover, different 5' end-mutated U1 snRNA expression plasmids were used to investigate the importance of the position +3 and of the two identified compensatory positions -1 and +4 in the recognition of 5'ss by the U1 snRNP. Overall, our findings establish general properties useful to molecular geneticists to identify nucleotide substitutions at position +3 that are more likely to alter splicing.

UMD-USHbases: a comprehensive set of databases to record and analyse pathogenic mutations and unclassified variants in seven Usher syndrome causing genes.

Using the Universal Mutation Database (UMD) software, we have constructed "UMD-USHbases", a set of relational databases of nucleotide variations for seven genes involved in Usher syndrome (MYO7A, CDH23, PCDH15, USH1C, USH1G, USH3A and USH2A). Mutations in the Usher syndrome type I causing genes are also recorded in non-syndromic hearing loss cases and mutations in USH2A in non-syndromic retinitis pigmentosa. Usher syndrome provides a particular challenge for molecular diagnostics because of the clinical and molecular heterogeneity. As many mutations are missense changes, and all the genes also contain apparently non-pathogenic polymorphisms, well-curated databases are crucial for accurate interpretation of pathogenicity. Tools are provided to assess the pathogenicity of mutations, including conservation of amino acids and analysis of splice-sites. Reference amino acid alignments are provided. Apparently non-pathogenic variants in patients with Usher syndrome, at both the nucleotide and amino acid level, are included. The UMD-USHbases currently contain more than 2,830 entries including disease causing mutations, unclassified variants or non-pathogenic polymorphisms identified in over 938 patients. In addition to data collected from 89 publications, 15 novel mutations identified in our laboratory are recorded in MYO7A (6), CDH23 (8), or PCDH15 (1) genes. Information is given on the relative involvement of the seven genes, the number and distribution of variants in each gene. UMD-USHbases give access to a software package that provides specific routines and optimized multicriteria research and sorting tools. These databases should assist clinicians and geneticists seeking information about mutations responsible for Usher syndrome.