Objectives First, to assess the performance of a prenatal diagnostic service using quantitative fluorescent polymerase chain reaction (QF-PCR)

This study demonstrates that the use of aCGH as a first line test is able to identify chromosomal mosaicism down to 9%, which is lower than the level reliably detected using standard cytogenetic analysis. aCGH avoids the disadvantages of culturing, which include culture bias, artifact, and culture failure.

Short oral presentation abstractsSupporting information can be found in the online version of this abstract OP17.07 Development of auditable standards in the first trimester ultrasound assessment of fetal blood flow through the ductus venosus and the tricuspid valve Objectives: To develop reference ranges for the ductus venosus (DV) and tricuspid valve (TV) waveforms at 11-14 weeks to define auditable standards to assess operator measurement performance. Methods: A single operator utilising the FMF criteria, prospectively obtained quantitative measurements for DV (pulsatility index for veins [PIV], pre-load index [PLI] and peak velocity for veins [PVIV]) and TV (E-wave peak velocity [EWPV], A-wave peak velocity [AWPV] and E-A ratio) to develop medians and 90% reference intervals. Measurement agreement studies between two experienced operators were also performed. The measurement bias of 3 additional operators was subsequently assessed using these auditable standards. Results: Doppler measurements were obtained in 292 patients (DV) and 321 patients (TV). Highly correlated DV indices indicated that only one reference range (for PIV) was necessary with a mean PIV measurement of 1.06 (90% RI 0.86 -1.23). As both EWPV and AWPV changed reliably over gestation, only the E-A ratio reference range was computed.Intra-observer and inter-observer studies on 30 additional patients of the DV PI and TV E-A ratio showed the within-operator agreement was almost perfect for DV PIV (ICC 0.82 -0.86) and strong for TV E-A ratio (ICC 0.68 -0.78) whilst the betweenoperator agreement was good for both DV PIV and TV E-A ratio measurements (ICC 0.46 for both).Preliminary audit using central tendency and dispersion of the measurements by 3 trained operators showed a tendency to overestimate DV PI (0.97, 1.07 and 1.09 MoM respectively; SD log PI 0.03-0.06) whilst the TV E-A ratio distribution met expectation (0.97, 0.98 and 0.98 MoM respectively; SD log E-A ratio 0.04 -0.1). Conclusions: Measurements of DV PIV and TV E-A ratio by experienced operators were found to be reproducible. Development of local reference ranges enabled the definition of quantitative auditable standards that can be utilized in assessment of operator training and ongoing Doppler measurement quality assurance.

Septins play key roles in mammalian cell division and cytokinesis but have not previously been implicated in a germline human disorder. A male infant with severe neutropenia and progressive dysmyelopoiesis with tetraploid myeloid precursors was identified. No known genetic etiologies for neutropenia or bone marrow failure were found. However, nextgeneration sequencing of germline samples from the patient revealed a novel, de novo germline stop-loss mutation in the X-linked gene SEPT6 that resulted in reduced SEPT6 staining in bone marrow granulocyte precursors and megakaryocytes. Patient skin fibroblast-derived induced pluripotent stem cells (iPSCs) produced reduced myeloid colonies, particularly of the granulocyte lineage. CRISPR/Cas9 knock-in of the patient's mutation or complete knock-out of SEPT6 was not tolerated in non-patient-derived iPSCs or human myeloid cell lines, but SEPT6 knock-out was successful in an erythroid cell line and resulting clones revealed a propensity to multinucleation. In silico analysis predicts that the mutated protein hinders the dimerization of SEPT6 coiled-coils in both parallel and antiparallel arrangements, which could in turn impair filament formation. These data demonstrate a critical role for SEPT6 in chromosomal segregation in myeloid progenitors that can account for the unusual predisposition to aneuploidy and dysmyelopoiesis.