Positive predictive values and outcomes for uninformative cell-free DNA tests: An Italian multicentric Cytogenetic and cytogenomic Audit of diagnOstic testing (ICARO study).

OBJECTIVES: To establish the positive predictive values (PPV) of cfDNA testing based on data from a nationwide survey of independent clinical cytogenetics laboratories. METHODS: Prenatal diagnostic test results obtained by Italian laboratories between 2013 and March 2020 were compiled for women with positive non-invasive prenatal tests (NIPT), without an NIPT result, and cases where there was sex discordancy between the NIPT and ultrasound. PPV and other summary data were reviewed. RESULTS: Diagnostic test results were collected for 1327 women with a positive NIPT. The highest PPVs were for Trisomy (T) 21 (624/671, 93%) and XYY (26/27, 96.3%), while rare autosomal trisomies (9/47, 19.1%) and recurrent microdeletions (8/55, 14.5%) had the lowest PPVs. PPVs for T21, T18, and T13 were significantly higher when diagnostic confirmation was carried out on chorionic villi (97.5%) compared to amniotic fluid (89.5%) (p < 0.001). In 19/139 (13.9%), of no result cases, a cytogenetic abnormality was detected. Follow-up genetic testing provided explanations for 3/6 cases with a fetal sex discordancy between NIPT and ultrasound. CONCLUSIONS: NIPT PPVs differ across the conditions screened and the tissues studied in diagnostic testing. This variability, issues associated with fetal sex discordancy, and no results, illustrate the importance of pre- and post-test counselling.

Two unrelated cases with biallelic CHEK2 variants:a novel condition with constitutional chromosomal instability?

Constitutional heterozygous mutations in CHEK2 gene have been associated with hereditary cancer risk. To date, only a few homozygous CHEK2 mutations have been reported in families with cancer susceptibility. Here, we report two unrelated individuals with a personal and familial cancer history in whom biallelic CHEK2 alterations were identified. The first case resulted homozygous for the CHEK2 c.793-1 G > A (p.Asp265Thrfs*10) variant, and the second one was found to be compound heterozygous for the c.1100delC (p.Thr367Metfs*15) and the c.1312 G > T (p.Asp438Tyr) variants. Multiple cytogenetic anomalies were demonstrated on peripheral lymphocytes of both patients. A literature revision showed that a single other CHEK2 homozygous variant was previously associated to a constitutional randomly occurring multi-translocation karyotype from peripheral blood in humans. We hypothesize that, at least some biallelic CHEK2 mutations might be associated with a novel disorder, further expanding the group of chromosome instability syndromes. Additional studies on larger cohorts are needed to confirm if chromosomal instability could represent a marker for CHEK2 constitutionally mutated recessive genotypes, and to investigate the cancer risk and the occurrence of other anomalies typically observed in chromosome instability syndromes.

Clinical Application of Easychip 8x15K Platform in 4106 Pregnancies Without Ultrasound Anomalies.

Clinical utility of Array-CGH Easychip 8x15K platform can be assessed by testing its ability to detect the occurrence of pathogenic copy number variants (CNVs), and occurrence of variants of uncertain significance (VoUS) in pregnancies without structural fetal malformations. The demand of chromosomal microarray analysis in prenatal diagnosis is progressively increasing in uneventful pregnancies. However, depending on such platform resolution, a genome-wide approach also provides a high risk of detecting VoUS and incidental finding (IF) also defined as "toxic findings." In this context, novel alternative strategies in probe design and data filtering are required to balance the detection of disease causing CNVs and the occurrence of unwanted findings. In a cohort of consecutive pregnancies without ultrasound anomalies, a total of 4106 DNA samples from cultured and uncultured amniotic fluid or chorionic villi were collected and analyzed by a previously designed Array-CGH mixed-resolution custom platform, which is able to detect pathogenic CNVs and structural imbalanced rearrangements limiting the identification of VoUS and IF. Pathogenic CNVs were identified in 88 samples (2.1%), 19 of which (0.5%) were undetectable by standard karyotype. VoUS accounted for 0.6% of cases. Our data confirm that a mixed-resolution and targeted array CGH platform, as Easychip 8x15K, yields a similar detection rate of higher resolution CMA platforms and reduces the occurrence of "toxic findings," hence making it eligible for a first-tier genetic test in pregnancies without ultrasound anomalies.

Comparative study of aCGH and Next Generation Sequencing (NGS) for chromosomal microdeletion and microduplication screening.

BACKGROUND: prenatal genetic diagnosis of rare disorders is undergoing in recent years a significant enhancement through the application of methods of massive parallel sequencing. Despite the quantity and quality of the data produced, just few analytical tools and software have been developed in order to identify structural and numerical chromosomal anomalies through NGS, mostly not compatible with benchtop NGS platform and routine clinical diagnosis. METHODS: we developed technical, bioinformatic, interpretive and validation pipelines for Next Generation Sequencing to identify SNPs, indels, aneuploidies, and CNVs (Copy Number Variations). RESULTS: we show a new targeted resequencing approach applied to prenatal diagnosis. For sample processing we used an enrichment method for 4,813 genes library preparation; after sequencing our bioinformatic pipelines allowed both SNPs analysis for approximately thirty diseases or diseases family involved in fetus development and numerical chromosomal anomalies screening. CONCLUSIONS: results obtained are compatible with those obtained through the gold standard technique, aCGH array, moreover allowing identification of genes involved in chromosome deletions or duplications and exclusion of point mutation on allele not affected by chromosome aberrations.

Next generation sequencing in the identification of a rare genetic disease from preconceptional couple screening to preimplantation genetic diagnosis.

INTRODUCTION: the use of Next Generation Sequencing (NGS) in the diagnosis of rare genetic pathologies is becoming ever more widespread in clinical practice. The following study reports the first case of preimplantation diagnosis through NGS of a form of LAMA2-related muscular dystrophy. CASE REPORT: a couple came to our Reproductive Medicine Centre for a preconceptional genetic consultation and for advice regarding secondary infertility. The couple already had a 3-year-old child who was suffering from a form of muscular dystrophy that has yet to be genetically defined. The disease had been diagnosed at the age of 6 months. A blood sample was taken from both parents and the child in order to analyze the DNA through the Illumina NextSeq 500 platform and an enrichment protocol, Trusight One Sequencing Panel, created by Illumina for the simultaneous sequencing of the exon regions of 4,813 clinically relevant genes. This led to the identification of 2 point mutations in the LAMA2 gene, each inherited by a parent. The couple then underwent a cycle of IVF (in vitro fertilization). A preimplantation genetic diagnosis was carried out on the embryos obtained after setting up a protocol for the analysis of a point mutation in the LAMA2 gene, (this mutation has yet to be described in literature) and the normal embryos together with the recessive LAMA2-related muscular dystrophy related carriers were transferred. There were no complications during pregnancy, which terminated with a cesarean section at 39 weeks and the birth of healthy 3430-gram baby. CONCLUSIONS: given its robustness, reliability and reproducibility, NGS could also be useful in prenatal diagnosis. This technique could guarantee an ample and quick analysis of the genes involved in development, making it possible to organize medical interventions during pregnancy and after birth.

Retrospective study evaluating the performance of a first-trimester combined screening for trisomy 21 in an Italian unselected population.

OBJECTIVES: to assess the performance of a combined first-trimester screening for trisomy 21 in an unselected Italian population referred to a specialized private center for prenatal medicine. METHODS: a retrospective validation of first-trimester screening algorithms [risk calculation based on maternal age and nuchal translucency (NT) alone, maternal age and serum parameters (free ß-hCG and PAPP-A) alone and a combination of both] for fetal aneuploidies evaluated in an unselected Italian population at Artemisia Fetal-Maternal Medical Centre in Rome. All measurements were performed between 11(+0) and 13(+6) weeks of gestation, between April 2007 and December 2008. RESULTS: of 3,610 single fetuses included in the study, we had a complete follow-up on 2,984. Fourteen of 17 cases of trisomy 21 were detected when a cut-off of 1:300 was applied [detection rate (DR) 82.4%, 95% confidence interval (CI) 64.2-100; false-positive rate (FPR) 4.7%, 95% CI 3.9-5.4; false-negative rate (FNR) 17.6%, 95% CI 0-35.8%]. CONCLUSION: in our study population the detection rate for trisomy 21, using the combined risk calculation based on maternal age, fetal NT, maternal PAPP-A and free ß-hCG levels, was superior to the application of either parameter alone. The algorithm has been validated for first trimester screening in the Italian population.

Prenatal Diagnosis of a Fetus with de novo Supernumerary Ring Chromosome 16 Characterized by Array Comparative Genomic Hybridization.

A fetus with de novo ring chromosome 16 is presented. At 20 weeks' gestation, ultrasound examination demonstrated bilateral clubfoot, bilateral renal pyelectasis, hypoplasia of the corpus callosum, and transposition of the great vessel. Amniocentesis was performed. Chromosome analysis identified a ring chromosome 16 [47,XY,r(16)] and array comparative genomic hybridization (a-CGH) demonstrated that the ring included the euchromatic portion 16p11.2. Postmortem examination confirmed prenatal findings. This is the first case of de novo ring chromosome 16 diagnosed prenatally with a new phenotypic pattern and also reinforces the importance of offering amniocentesis with a-CGH if fetal anomalies are detected.

The use of DHPLC (Denaturing High Performance Liquid Chromatography) in II level screening of the CFTR gene in Prenatal Diagnosis.

OBJECTIVE: The aim of the study is to evaluate the role of Denaturing High Performance Liquid Chromatography (DHPLC) in the second level screening of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. METHODS: A 9-month prospective study, between June 2008 and March 2009 at Artemisia Fetal Medical Centre, included 3829 samples of amniotic fluid collected from women undergoing mid-trimester amniocentesis.The genetic diagnosis of CF was based on research of the main mutations of the CFTR gene on fetal DNA extracted from the amniocytes, (first level screening) using different commercial diagnostic systems. A second level screening using DHPLC, on the amniotic fluid and on a blood sample from the couple, was offered in case of fetuses heterozygous at first level screening. RESULTS: Of 3829 fetuses, 134 were found to be positive, 129 heterozygous and 5 affected. Of the 129 couples, following appropriate genetic counselling, 53 requested a second level screening. Through the use of DHPLC, 44 couples were found to be negative, and in nine couples, nine rare mutations were identified. CONCLUSIONS: The first level screening can be useful to evidence up to 75% of the CF mutations. The second level screening can identify a further 10% of mutant alleles. DHPLC was found to be a reliable and specific method for the rapid identification of the rare CFTR mutations which were not revealed in initial first level screening.

Prenatal screening of Cystic Fibrosis: a single centre experience.

OBJECTIVE: The gene responsible for the pathogenesis of cystic fibrosis has been known for over 15 years and represent the most common autosomal recessive disease in the european population. We aimed to investigate the incidence of this condition during fetal life. METHODS: In the past 10 years we examined in our centre 25393 fetuses of women underwent to amniocentesis. We carried out the examination of the most frequent mutations which enable, according to the literature data, the identification of almost 80% of the affected alleles. RESULT: We identified 922 heterozygous and 9 homozygous for the mutation. The frequency of heterozygousin the examined sample was 1/27,5 while that of the affected was 1/2821. CONCLUSION: We encourage new thoughts regarding the diagnostic validity of the most frequent panel of mutations among the italian population in order to exclude never encountered mutations and the insertion of other more significant mutations.