Marta Rodriguez de Alba

New strategy for the prenatal detection/exclusion of paternal cystic fibrosis mutations in maternal plasma

BACKGROUND Since the presence of fetal DNA was discovered in maternal blood, different investigations have focused on non-invasive prenatal diagnosis. The analysis of fetal DNA in maternal plasma may allow the diagnosis of fetuses at risk of cystic fibrosis (CF) without any risk of fetal loss. Here, we present a new strategy for the detection of fetal mutations causing CF in maternal plasma. METHODS We have used a mini-sequencing based method, the SNaPshot, for fetal genotyping of the paternal mutation in maternal blood from three pregnancies at risk of CF. RESULTS The paternal mutation was detected in the analysis of plasma samples from cases 1 and 3 but not in case 2. Results of a posterior conventional molecular analysis of chorionic biopsies were in full agreement with those obtained from analysis of the plasma samples. CONCLUSIONS The knowledge about the inheritance of the paternal mutation in a fetus may avoid the conventional prenatal diagnosis in some cases. The SNaPshot technique has been shown to be a sensitive and accurate method for the detection of fetal mutations in maternal plasma. Its ease handling, rapid and low cost makes it appropriate for a future routine clinical use in non-invasive prenatal diagnosis of cystic fibrosis.

Non-invasive prenatal diagnosis of single-gene disorders from maternal blood

Prenatal diagnosis (PD) is available for pregnancies at risk of monogenic disorders. However, PD requires the use of invasive obstetric techniques for fetal-sample collection and therefore, involves a risk of fetal loss. Circulating fetal DNA in the maternal bloodstream is being used to perform non-invasive prenatal diagnosis (NIPD). NIPD is a challenging discipline because of the biological features of the maternal blood sample. Maternal blood is an unequal mixture of small (and fragmented) amounts of fetal DNA within a wide background of maternal DNA. For this reason, initial NIPD studies have been based on the analysis of specific paternally inherited fetal tracts not present in the maternal genome so as to ensure their fetal origin. Following this strategy, different NIPD studies have been carried out, such as fetal-sex assessment for pregnancies at risk of X-linked disorders, RhD determination, and analysis of single-gene disorders with a paternal origin. The study of the paternal mutation can be used for fetal diagnosis of dominant disorders or to more accurately assess the risk of an affected child in case of recessive diseases. Huntingtons disease, cystic fibrosis, or achondroplasia are some examples of diseases studied using NIPD. New technologies are opening NIPD to the analysis of maternally inherited fetal tracts. NIPD of trisomy 21 is the latest study derived from the use of next-generation sequencing (NGS).

Application of Fetal DNA Detection in Maternal Plasma: A Prenatal Diagnosis Unit Experience

Non-invasive prenatal diagnosis tests based on the analysis of fetal DNA in maternal plasma have potential to be a safer alternative to invasive methods. So far, different studies have shown mainly fetal sex, fetal RhD, and quantitative variations of fetal DNA during gestation with fetal chromosomal anomalies or gestations at risk for preeclampsia. The objective of our research was to evaluate the use of fetal DNA in maternal plasma for clinical application. In our study, we have established the methodology needed for the analysis of fetal DNA. Different methods were used, according to the requirements of the assay. We have used quantitative fluorescent polymerase chain reaction (QF-PCR) to perform fetal sex detection with 90% sensitivity. The same technique permitted the detection of fetal DNA from the 10th week of gestation to hours after delivery. We have successfully carried out the diagnosis of two inherited disorders, cystic fibrosis (conventional PCR and restriction analysis) and Huntington disease (QF-PCR). Ninety percent of the cases studied for fetal RhD by real-time PCR were correctly diagnosed. The detection of fetal DNA sequences is a reality and could reduce the risk of invasive techniques for certain fetal disorders in the near future.

Choroideremia, sensorineural deafness, and primary ovarian failure in a woman with a balanced X-4 translocation

We present clinical and cytogenetic studies of a female patient affected with choroideremia, mild sensorineural deafness, and primary amenorrhea showing a balanced translocation between chromosomes X and 4. The breakpoint was precisely defined applying FISH techniques: 46,X,t(X;4)(q21.2;p16.3).ish t(X;4)(D4S96+, D4F26+; wcpX+). The X-chromosomal breakpoint was located within a region where both the choroideremia locus and a deafness locus (DFN3/POU3F4) have been mapped. The presence of X-linked disorders in this balanced carrier of X-autosomal translocations (XAT) can be explained either by the disruption of the structural coding or regulatory sequences of the gene(s) or by the submicroscopic deletion of this region leading to a contiguous gene deletion syndrome. The primary ovarian failure (POF) found in the present case has been already observed in XAT when the breakpoint is within a previously defined critical region (Xq13-26). A position effect is postulated as a possible explanation.

Prenatal diagnosis in maternal plasma of a fetal mutation causing propionic acidemia

Prenatal diagnosis (PD) is available to families affected with propionic acidemia (PA), however, it entails a risk of miscarriage. Fetal DNA circulating in maternal blood could allow performing a safe prenatal diagnosis of fetal mutations. Exclusion of the paternal mutation in maternal plasma may avoid conventional PD in cases of recessive disorders such us PA. In this work, we have correctly diagnosed in maternal plasma the status of a fetus at risk of PA for the paternal mutation.

Detection of a Paternally Inherited Fetal Mutation in Maternal Plasma by the Use of Automated Sequencing

Abstract:  The discovery of circulating fetal DNA in maternal blood has been an encouraging step forward in the prenatal diagnostic field. It has opened up the possibility of development of a noninvasive method for the genetic analysis of the fetus. Many techniques have been applied to the study of this fetal DNA, but automated sequencing has been seldom used. The intention of this study was to use the automated sequencing technique for the detection of a paternally inherited fetal mutation in maternal plasma. Maternal plasma samples from a pregnant woman, whose husband had a mutation (Q134X) in the RP2 gene, which is located in the X‐chromosome, were collected at two different gestational ages (10th and 19th week of gestation) in order to determine whether the paternally inherited fetal mutation could be detected by automated sequencing. Restriction analysis was also performed to confirm the results. The fetal mutation was clearly detected in the maternal plasma by the use of automated sequencing. The automated sequencing enables the possibility of analyzing fetal sequences, at a nucleotide level, in order to detect mutations or polymorphisms which are distinguishable from maternal sequences.

Noninvasive prenatal diagnosis using ccffDNA in maternal blood: state of the art.

Owing to the risk of fetal loss associated with prenatal diagnostic procedures, the last decade has seen great developments in noninvasive prenatal diagnosis (NIPD). The discovery of circulating cell-free fetal DNA (ccffDNA) in maternal plasma has opened new lines of research in alternative technologies that may facilitate safe diagnosis. Because ccffDNA represents only a small fraction of all DNA present in maternal plasma and it is masked by the background of maternal DNA, the scope of NIPD was, until recently, limited to the study of paternal DNA sequences (i.e., detection of SRY sequences, RhD gene in RhD-negative women and paternally inherited single-gene disorders, such as cystic fibrosis and Huntington’s disease). However, new discoveries and technology are making NIPD a real option for patients and providing for an array of clinical applications, such as molecular studies in high-risk families, general screening and pregnancy management.

Fetal Genotyping in Maternal Blood by Digital PCR: Towards NIPD of Monogenic Disorders Independently of Parental Origin

Purpose To date, non-invasive prenatal diagnosis (NIPD) of monogenic disorders has been limited to cases with a paternal origin. This work shows a validation study of the Droplet Digital PCR (ddPCR) technology for analysis of both paternally and maternally inherited fetal alleles. For the purpose, single nucleotide polymorphisms (SNPs) were studied with the only intention to mimic monogenic disorders. Methods NIPD SNP genotyping was performed by ddPCR in 55 maternal plasma samples. In 19 out of 55 cases, inheritance of the paternal allele was determined by presence/absence criteria. In the remaining 36, determination of the maternally inherited fetal allele was performed by relative mutation dosage (RMD) analysis. Results ddPCR exhibited 100% accuracy for detection of paternal alleles. For diagnosis of fetal alleles with maternal origin by RMD analysis, the technology showed an accuracy of 96%. Twenty-nine out of 36 were correctly diagnosed. There was one FP and six maternal plasma samples that could not be diagnosed. Discussion In this study, ddPCR has shown to be capable to detect both paternal and maternal fetal alleles in maternal plasma. This represents a step forward towards the introduction of NIPD for all pregnancies independently of the parental origin of the disease.

Noninvasive prenatal diagnosis of monogenic disorders

Introduction: Since the presence of circulating cell-free fetal DNA (ccffDNA) in maternal peripheral blood was demonstrated in 1997, great efforts have been done in order to use this source of fetal material for noninvasive prenatal diagnosis. The advantage that it represents is avoiding the obstetric invasive procedures required for conventional prenatal diagnosis. Areas covered: Efforts are mainly focused on finding the most accurate way to diagnose the most common fetal aneuploidies, paying special attention to trisomy 21. Recent advances in technology offer new diagnostic tools with high degrees of sensitivity thus generating great expectations for this type of diagnosis. However, there are other reasons why pregnant women undergo conventional prenatal diagnosis. Being at risk of transmitting a monogenic disorder is one of them. And although the percentage of those pregnancies may represent a small percentage of the diagnosis performed in the first trimester, these numbers should not be underestimated. Expert opinion: Management of pregnancies at risk of an X-linked Mendelian disorder has changed thanks to the noninvasive fetal sex assessment. As for other Mendelian disorders, until recently, their study was limited to those cases paternally inherited. Nevertheless, the new emerging technologies are also opening the scope to maternally inherited disorders.

Turner phenotype in a girl with a 45,X/46,XX/ 47,XX, +18 mosaicism

We report a girl with Turner syndrome phenotype, whose karyotype on amniocyte culture was 45,X, while cytogenetic analysis on peripheral blood lymphocytes showed the presence of a mosaic chromosome constitution with three different cell lines: 45,X[5]/46,XX[3]/47,XX,+18 [35]. No signs of trisomy 18 were observed and a follow up during childhood revealed normal psychomotor development. Parental origin and mechanism of formation were studied using high polymorphic microsatellites and Quantitative Fluorescent PCR. The 18‐trisomic cells showed one paternal allele and two maternal homozygous alleles at different loci of chromosome 18, suggesting a maternal M‐II meiotic or a postzygotic error. A biparental origin of the X‐alleles in the trisomic cells were determined, being the paternal allele retained in the 45,X cells. The possible mechanism of formation implying meiotic and/or mitotic errors is discussed.