Expanded carrier screening for reproductive risk assessment: An evidence-based practice guideline from the National Society of Genetic Counselors.

Expanded carrier screening (ECS) intends to broadly screen healthy individuals to determine their reproductive chance for autosomal recessive (AR) and X-linked (XL) conditions with infantile or early-childhood onset, which may impact reproductive management (Committee Opinion 690, Obstetrics and Gynecology, 2017, 129, e35). Compared to ethnicity-based screening, which requires accurate knowledge of ancestry for optimal test selection and appropriate risk assessment, ECS panels consist of tens to hundreds of AR and XL conditions that may be individually rare in various ancestries but offer a comprehensive approach to inherited disease screening. As such, the term "equitable carrier screening" may be preferable. This practice guideline provides evidence-based recommendations for ECS using the GRADE Evidence to Decision framework (Guyatt et al., BMJ, 2008, 336, 995; Guyatt et al., BMJ, 2008, 336, 924). We used evidence from a recent systematic evidence review (Ramdaney et al., Genetics in Medicine, 2022, 20, 374) and compiled data from peer-reviewed literature, scientific meetings, and clinical experience. We defined and prioritized the outcomes of informed consent, change in reproductive plans, yield in identification of at-risk carrier pairs/pregnancies, perceived barriers to ECS, amount of provider time spent, healthcare costs, frequency of severely/profoundly affected offspring, incidental findings, uncertain findings, patient satisfaction, and provider attitudes. Despite the recognized barriers to implementation and change in management strategies, this analysis supported implementation of ECS for these outcomes. Based upon the current level of evidence, we recommend ECS be made available for all individuals considering reproduction and all pregnant reproductive pairs, as ECS presents an ethnicity-based carrier screening alternative which does not rely on race-based medicine. The final decision to pursue carrier screening should be directed by shared decision-making, which takes into account specific features of patients as well as their preferences and values. As a periconceptional reproductive risk assessment tool, ECS is superior compared to ethnicity-based carrier screening in that it both identifies more carriers of AR and XL conditions as well as eliminates a single race-based medical practice. ECS should be offered to all who are currently pregnant, considering pregnancy, or might otherwise biologically contribute to pregnancy. Barriers to the broad implementation of and access to ECS should be identified and addressed so that test performance for carrier screening will not depend on social constructs such as race.

The impact of HBB-related hemoglobinopathies carrier status on fetal fraction in noninvasive prenatal screening.

OBJECTIVE: We evaluated whether there is an association between ß-globin (HBB) pathogenic variants and fetal fraction (FF), and whether the association has a clinically relevant impact on non-invasive prenatal screening (NIPS). METHOD: A whole-genome sequencing NIPS laboratory database was retrospectively queried for women who underwent NIPS and carrier screening of both HBB and the α-globin genes (HBA1/HBA2). Women affected with either condition were excluded from the study, yielding a cohort size of 15,853. A "corrected FF" was obtained via multivariable linear regression adjusted for the systematic impacts of maternal age, gestational age and BMI. Corrected FF distributions of HBB and HBA1/HBA2 carriers were each compared to non-carriers using the Kolmogorov-Smirnov test. RESULTS: In this cohort, 291 women were carriers for HBB alone, and 1016 were carriers for HBA1/HBA2 alone. The HBB carriers had a lower corrected FF when compared to non-carriers (p < 0.0001). There was no difference in corrected FF among carriers and non-carriers of HBA1/HBA2. CONCLUSION: Carriers of pathogenic variants in the HBB gene, but not the HBA1/HBA2 genes, are more likely to have lower FF when compared to women with structurally normal hemoglobin. This decrease in FF could result in an elevated test-failure rate if FF thresholds were used.

Homozygous TANGO2 Single Nucleotide Variants Presenting with Additional Manifestations Resembling Alternating Hemiplegia of Childhood-Expanding the Phenotype of a Recently Reported Condition.

CASE: We report a 15-year-old Indian girl born to a consanguineous couple, who presented with epilepsy, developmental delay, neuroregression, and episodes of alternating hemiparesis. In addition, she had one episode of rhabdomyolysis at the age of 7 years. Extensive genetic and metabolic work up through the years was unrevealing. Eventually a trio whole exome sequencing (WES) revealed homozygous single nucleotide variants in TANGO2 gene. DISCUSSION: TANGO2 related recurrent metabolic crises with encephalomyopathy and cardiac arrhythmias were described very recently and only 15 cases were reported in literature at the time of writing. Alternating hemiplegia of childhood which was seen in our patient, has not been described in previous patients with TANGO2 mutation, and thereby expands the emerging phenotypic spectrum of this novel entity. This report also reiterates the utility of WES in diagnosing newly recognized neurogenetic conditions.

Prenatal Lethal Diagnosis of 8p23.1 Duplication Syndrome Associated with Omphalocele and Encephalocele.

Despite increased prenatal and postnatal use of array comparative genomic hybridization (aCGH), isolated 8p23.1 duplication remains rare and has been associated with a widely variable phenotype. Here, we report an isolated 8p23.1 duplication in a fetus with an omphalocele and encephalocele that were incompatible with life. Prenatal aCGH demonstrated a 3.75 Mb de novo duplication of 8p23.1. This region encompassed 54 genes, 21 of which are described in OMIM, including SOX7 and GATA4. The summarized case demonstrates phenotypic features not previously described in 8p23.1 duplication syndrome and is reported in order to enhance understanding of the phenotypic variation.

A Diagnosis of Maternal 22q Duplication and Mosaic Deletion following Prenatal Cell-Free DNA Screening.

Concurrent microduplication and microdeletion of the chromosome 22q11.2 region are a rarely reported phenomenon. We describe a case of germline 22q11.21 microduplication syndrome with concurrent mosaic 22q11.2 deletion in a pregnant patient, identified by chromosomal microarray and FISH after noninvasive prenatal genetic screening (cfDNA) results discordant with family history. The patient was referred to maternal-fetal medicine (MFM) at 14 weeks' gestation secondary to an SNP-based cfDNA result of a suspected maternal 22q11.2 deletion and a fetal risk of 1 in 2 for 22q11.2 deletion syndrome. The patient reported a similar cfDNA result in a previous pregnancy; however postnatal chromosomal microarray on that child identified an atypical 22q11.21 microduplication. We report the maternal chromosomal microarray findings of a germline 726 kb 22q11.21 duplication and a mosaic 1.33 Mb 22q11.2 deletion and highlight the copy number variant data generated by cfDNA in this unique case. This family adds to the limited literature of concurrent 22q11.2 microduplication and microdeletion carriers.

The association of HBB-related significant hemoglobinopathies and low fetal fraction on noninvasive prenatal screening for fetal aneuploidy.

OBJECTIVES: HBB-related significant hemoglobinopathies have been anecdotally associated with low fetal fraction on noninvasive prenatal screening (NIPS). We sought to compare the difference in fetal fraction using NIPS in women with HBB-related significant hemoglobinopathies (HSH) and women with normal hemoglobin. STUDY DESIGN: This is a retrospective case-control study. Cases were women with a diagnosis of HSH using NIPS from a commercial laboratory. The comparison group was women with hemoglobin AA from a tertiary care center database. We tested for differences in median fetal fraction using quantile regression analysis, adjusting for maternal body weight and gestational age. RESULTS: This study includes 35 women with clinically significant HSH and a comparison group of 636 women with hemoglobin AA. Adjusting for gestational age and body weight, the median fetal fraction was 4.1 point lower in the HSH than in the comparison group (ß - 4.1; 95% -5.7 to -2.5, p < .05). The rate of no-calls due to low fetal fraction was significantly higher in the clinically significant HSH group than in the comparison group [HSH: n = 9/35, 25.7% versus comparison: n = 32/636, 5.0% (p < .001)]. CONCLUSION: Women with HSH were more likely to have a lower fetal fraction and ultimately a five-fold higher no-call rate. What's already known about this topic?Low fetal fraction is one of the most common causes of no-call result in noninvasive prenatal screeningHigh maternal weight, early gestational age and fetal aneuploidies are associated with low fetal fraction What does this study add?HBB-related significant hemoglobinopathies are associated with low fetal fractionReduction in fetal fraction due to HBB-related significant hemoglobinopathies may also result in higher no-call rate.

False Low-Risk Single Nucleotide Polymorphism-Based Noninvasive Prenatal Screening in Pentasomy 49,XXXXY.

Introduction Pentasomy 49,XXXXY is a sex chromosome anomaly difficult to be diagnosed prenatally. We describe a patient of pentasomy 49,XXXXY with false low-risk results using a noninvasive prenatal screening (NIPS). A 30-year-old G1P0 woman presented at 33 6/7 weeks, secondary to sonographic fetal anomalies. She had low-risk NIPS at 13 6/7 weeks. Anatomy survey showed bilateral clubfeet, clinodactyly of the left fifth digit, micropenis, and echogenic bowel. Cytogenetics analysis revealed pentasomy 49,XXXXY syndrome. We report third-trimester sonographic features of a fetus with pentasomy 49,XXXXY and the importance of thorough pre- and posttest counseling for NIPS.

Evolution of Brain Glucose Metabolic Abnormalities in Children With Epilepsy and SCN1A Gene Variants.

Three children with drug-refractory epilepsy, normal magnetic resonance image (MRI), and a heterozygous SCN1A variant underwent 2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET) scanning between age 6 months and 1 year and then at age 3 years 6 months to 5 years 5 months. Regional FDG uptake values were compared to those measured in age- and gender-matched pseudo-controls. At baseline, the brain glucose metabolic pattern in the SCN1A group was similar to that of the pseudo-controls. At follow-up, robust decreases of normalized FDG uptake was found in bilateral frontal, parietal and temporal cortex, with milder decreases in occipital cortex. Children with epilepsy and an SCN1A variant have a normal pattern of cerebral glucose metabolism at around 1 year of age but develop bilateral cortical glucose hypometabolism by age 4 years, with maximal decreases in frontal, parietal, and temporal cortex. This metabolic pattern may be characteristic of epilepsy associated with SCN1A variants and may serve as a biomarker to monitor disease progression and response to treatments.