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Objective: In the absence of aneuploidy or other pathogenic cytogenetic abnormality, fetuses with increased nuchal translucency (NT ≥ 3.5 mm) and/or other sonographic abnormalities have a greater incidence of genetic syndromes, but defining the underlying pathology can be challenging. Here, we investigate the value of whole exome sequencing in fetuses with sonographic abnormalities but normal microarray analysis., Method: Whole exome sequencing was performed on DNA extracted from chorionic villi or amniocytes in 24 fetuses with unexplained ultrasound findings. In the first 14 cases sequencing was initially performed on fetal DNA only. For the remaining 10, the trio of fetus, mother and father was sequenced simultaneously., Results: In 21% (5/24) cases, exome sequencing provided definitive diagnoses (Milroy disease, hypophosphatasia, achondrogenesis type 2, Freeman-Sheldon syndrome and Baraitser-Winter Syndrome). In a further case, a plausible diagnosis of orofaciodigital syndrome type 6 was made. In two others, a single mutation in an autosomal recessive gene was identified, but incomplete sequencing coverage precluded exclusion of the presence of a second mutation., Conclusion: Whole exome sequencing improves prenatal diagnosis in euploid fetuses with abnormal ultrasound scans. In order to expedite interpretation of results, trio sequencing should be employed, but interpretation can still be compromised by incomplete coverage of relevant genes., (© 2015 John Wiley & Sons, Ltd.)

Objective: Accurate prenatal diagnosis of genetic conditions can be challenging and usually requires invasive testing. Here, we demonstrate the potential of next-generation sequencing (NGS) for the analysis of cell-free DNA in maternal blood to transform prenatal diagnosis of monogenic disorders., Methods: Analysis of cell-free DNA using a PCR and restriction enzyme digest (PCR-RED) was compared with a novel NGS assay in pregnancies at risk of achondroplasia and thanatophoric dysplasia., Results: PCR-RED was performed in 72 cases and was correct in 88.6%, inconclusive in 7% with one false negative. NGS was performed in 47 cases and was accurate in 96.2% with no inconclusives. Both approaches were used in 27 cases, with NGS giving the correct result in the two cases inconclusive with PCR-RED., Conclusion: NGS provides an accurate, flexible approach to non-invasive prenatal diagnosis of de novo and paternally inherited mutations. It is more sensitive than PCR-RED and is ideal when screening a gene with multiple potential pathogenic mutations. These findings highlight the value of NGS in the development of non-invasive prenatal diagnosis for other monogenic disorders., (© 2015 John Wiley & Sons, Ltd.)

Recently, we have witnessed the rapid translation into clinical practice of non-invasive prenatal testing for the common aneuploidies, most notably within the United States and China. This represents a lucrative market with testing being driven by companies developing and offering their services. These tests are currently aimed at women with high/medium-risk pregnancies identified by serum screening and/or ultrasound scanning. Uptake has been impressive, albeit limited to the commercial sector. However, non-invasive prenatal diagnosis (NIPD) for single-gene disorders has attracted less interest, no doubt because this represents a much smaller market opportunity and in the majority of cases has to be provided on a bespoke, patient or disease-specific basis. The methods and workflows are labour-intensive and not readily scalable. Nonetheless, there exists a significant need for NIPD of single-gene disorders, and the continuing advances in technology and data analysis should facilitate the expansion of the NIPD test repertoire. Here, we review the progress that has been made to date, the different methods and platform technologies, the technical challenges, and assess how new developments may be applied to extend testing to a wider range of genetic disorders., (© 2013 John Wiley & Sons, Ltd.)

Originally prenatal diagnosis was confined to the diagnosis of metabolic disorders and depended on assaying enzyme levels in amniotic fluid. With the development of recombinant DNA technology, molecular diagnosis became possible for some genetic conditions late in the 1970s. Here we briefly review the history of molecular prenatal diagnostic testing, using Duchenne muscular dystrophy as an example, and describe how over the last 30 years we have moved from offering testing to a few affected individuals using techniques, such as Southern blotting to identify deletions, to more rapid and accurate PCR-based testing which identifies the precise change in dystrophin for a greater number of families. We discuss the potential for safer, earlier prenatal genetic diagnosis using cell free fetal DNA in maternal blood before concluding by speculating on how more recent techniques, such as next generation sequencing, might further impact on the potential for molecular prenatal testing. Progress is not without its challenges, and as cytogenetics and molecular genetics begin to unite into one, we foresee the main challenge will not be in identifying the genetic change, but rather in interpreting its significance, particularly in the prenatal setting where we frequently have no phenotype on which to base interpretation., ((c) 2010 John Wiley & Sons, Ltd.)

Several different recessive mutations in the connexin26 (Cx26; beta 2) gene have been associated with non-syndromic hereditary deafness. This suggests gap junctions are important to cochlear function. Numerous large gap junctions are present between adjacent supporting cells in both the vestibular and auditory sensory epithelia of the mature inner ear. In vestibular organs, Cx26 is highly expressed, but antibodies of Cx32 (beta 1) also label the supporting cells. In the organ of Corti of the cochlea, Cx26 is the predominant connexin isoform; neither Cx32 nor Cx43 (alpha 1) can be detected by immunohistochemistry. One role for gap junctions between supporting cells may be to provide a pathway for the rapid removal of ions away from the region of the sensory cells during transduction in order to maintain sensitivity. In the cochlea gap junctions are also associated with the basal cells of the stria vascularis, an ion-transporting epithelium that maintains a positive electrical potential in the potassium-rich endolymph fluid which bathes the apical surfaces of the sensory 'hair' cells and which is crucial for auditory transduction. Gap junctions are present between fibrocytes in the spiral ligament that underlies the stria vascularis, and between these fibrocytes and strial basal cells. During cochlear development, the initial formation and subsequent increase in size and number of gap junctions in the stria vascularis coincides with the initial generation and rise of the endocochlear potential. This and other evidence suggests that one role of gap junctions in the cochlea is to provide a pathway for passage of ions to maintain endolymph and, thus, auditory acuity. Mutations to Cx26 could, therefore, disrupt this ion circulation, resulting in deafness.