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Background: We aimed to analyse the efficacy and added value of a targeted Israeli expanded carrier screening panel (IL-ECSP), beyond the first-tier test covered by the Israeli Ministry of Health (IMOH) and the second-tier covered by the Health Maintenance Organisations (HMOs)., Methods: A curated variant-based IL-ECSP, tailored to the uniquely diverse Israeli population, was offered at two tertiary hospitals and a major genetics laboratory. The panel includes 1487 variants in 357 autosomal recessive and X-linked genes., Results: We analysed 10 115 Israeli samples during an 18-month period. Of these, 6036 (59.7%) were tested as couples and 4079 (40.3%) were singles. Carriers were most frequently identified with mutations in the following genes: GJB2/GJB6 (1:22 allele frequency), CFTR (1:28), GBA (1:34), TYR (1:39), PAH (1:50), SMN1 (1:52) and HEXA (1:56). Of 3018 couples tested, 753 (25%) had no findings, in 1464 (48.5%) only one partner was a carrier, and in 733 (24.3%) both were carriers of different diseases. We identified 79 (2.6%) at-risk couples, where both partners are carriers of the same autosomal recessive condition, or the female carries an X-linked disease. Importantly, 48.1% of these would not have been detected by ethnically-based screening tests currently provided by the IMOH and HMOs, for example, variants in GBA, TYR, PAH and GJB2/GJB6 ., Conclusion: This is the largest cohort of targeted ECSP testing, tailored to the diverse Israeli population. The IL-ECSP expands the identification of couples at risk and empowers their reproductive choices. We recommend endorsing an expanded targeted panel to the National Genetic Carrier Screening programme., Competing Interests: Competing interests: DMB was involved in the design of the CarrierScan array and is entitled to certain royalties., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

The complement system regulator CD55 was initially found to carry the Cromer blood group system antigens, and its complete loss of function was subsequently revealed to cause a severe monogenic gastrointestinal syndrome characterized by protein-losing enteropathy and susceptibility to venous thrombosis. Here we present homozygosity to the CD55 c.596C>T; p.Ser199Leu variant, which was previously described as the Cromer Dr(a-) genotype, in two Bukharan Jewish CD55-deficiency patients with variable disease severity. We confirm that this missense variant causes aberrant splicing and deletion of 44 bp in exon 5, leading to premature termination and low expression of the CD55 protein. Furthermore, Patient 1 exhibited a mildly abnormal B cell immunophenotyping profile. By population screening we established that this variant is highly prevalent in the Bukharan Jewish population, with a carrier frequency of 1:17, suggesting that many similar patients are un- or mis-diagnosed. The phenotypic variability, ranging from abdominal pain when eating a high-fat diet to the full CD55-deficiency phenotype, is likely related to modifiers affecting the proportion of the variant that is able to escape aberrant splicing. Establishing the diagnosis of CD55-deficiency in a timely manner, even in patients with milder symptoms, may have a critical effect on their management and quality-of-life since treatment with the complement inhibitor eculizumab is highly effective in ameliorating disease manifestations. Awareness of founder mutations within certain populations can further guide genetic testing and prevent a diagnostic odyssey, by placing this CD55 variant high on the differential diagnosis., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

PurposeTo compare the frequency of copy-number variants (CNVs) of variable penetrance in low-risk and high-risk prenatal samples and postnatal samples.MethodsTwo cohorts were categorized according to chromosomal microarray analysis (CMA) indication: group I, low-risk prenatal-women with uneventful pregnancy (control group); group II, high-risk prenatal-women whose fetuses had congenital malformations; and group III, postnatal-individuals with unexplained developmental delay/intellectual disability, autism spectrum disorders, or multiple congenital anomalies. CNVs were categorized based on clinical penetrance: (i) high (>40%), (ii) moderate (10-40%), and (iii) low (<10%).ResultsFrom 2013 to 2016, 21,594 CMAs were performed. The frequency of high-penetrance CNVs was 0.1% (21/15,215) in group I, 0.9% (26/2,791) in group II, and 2.6% (92/3,588) in group III. Moderate-penetrance CNV frequency was 0.3% (47/15,215), 0.6% (19/2,791), and 1.2% (46/3,588), respectively. These differences were statistically significant. The frequency of low-penetrance CNVs was not significantly different among groups: 0.6% (85/15,215), 0.9% (25/2,791), and 1.0% (35/3,588), respectively.ConclusionHigh-penetrance CNVs might be a major factor in the overall heritability of developmental, intellectual, and structural anomalies. Low-penetrance CNV alone does not seem to contribute to these anomalies. These data may assist pre- and posttest CMA counseling.

Background: The temporal order of allelic replication is interrelated to the epigenomic profile. A significant epigenetic marker is the asynchronous replication of monoallelically-expressed genes versus the synchronous replication of biallelically-expressed genes. The present study sought to determine whether a microdeletion in the genome affects epigenetic profiles of genes unrelated to the missing segment. In order to test this hypothesis, we checked the replication patterns of two genes - SNRPN, a normally monoallelically expressed gene (assigned to 15q11.13), and the RB1, an archetypic biallelically expressed gene (assigned to 13.q14) in the genomes of patients carrying the 22q11.2 deletion (DiGeorge/Velocardiofacial syndrome) and those carrying the 7q11.23 deletion (Williams syndrome)., Results: The allelic replication timing was determined by fluorescence in situ hybridization (FISH) technology performed on peripheral blood cells. As expected, in the cells of normal subjects the frequency of cells showing asynchronous replication for SNRPN was significantly (P < 10-12) higher than the corresponding value for RB1. In contrast, cells of the deletion-carrying patients exhibited a reversal in this replication pattern: there was a significantly lower frequency of cells engaging in asynchronous replication for SNRPN than for RB1 (P < 10-4 and P < 10-3 for DiGeorge/Velocardiofacial and Williams syndromes, respectively). Accordingly, the significantly lower frequency of cells showing asynchronous replication for SNRPN than for RB1 is a new epigenetic marker distinguishing these deletion syndrome genotypes from normal ones., Conclusion: In cell samples of each deletion-carrying individual, an aberrant, reversed pattern of replication is delineated, namely, where a monoallelic gene replicates more synchronously than a biallelic gene. This inverted pattern, which appears to be non-deletion-specific, clearly distinguishes cells of deletion-carriers from normal ones. As such, it offers a potential epigenetic marker for suspecting a hidden microdeletion that is too small to be detected by conventional karyotyping methods.

Velocardiofacial syndrome (VCFS) is caused by a microdeletion in chromosome 22 and is a risk factor for the development of schizophrenia and other psychiatric disorders. The catechol-O-methyltransferase (COMT), residing in the 22q11.2 microdeletion region, is a major candidate gene for genetic susceptibility to neuropsychiatric disorders in VCFS. Individuals with VCFS carrying the low-activity allele (COMTL) are expected to have the lowest possible COMT activity since they have only a single copy of the gene. We explored the possibility that COMTL is associated with psychiatric disorders commonly found in VCFS. Fifty-five unrelated individuals with VCFS underwent psychiatric evaluation and were genotyped for the COMT 158Val/Met polymorphism coding for COMT high/low-activity alleles. The COMTL allele was significantly more prevalent in VCFS subjects with attention deficit hyperactivity disorder (ADHD) (73.9% vs. 33.3%, OR 5.67, chi2=7.76, p=0.005) and obsessive-compulsive disorder (OCD) (78.6% vs. 33.3%, OR 7.33, chi2=7.24, p=0.007) than in the control group (VCFS subjects without OCD, ADHD and schizophrenia/schizoaffective (SZ/SZaff) disorder). The results of this study suggest that greatly reduced COMT activity, as expected in VCFS COMTL individuals may be a risk factor for psychiatric sequelae in this population. Future longitudinal studies focusing on additional COMT polymorphic sites and other candidate genes from the deleted region will elucidate the molecular pathways leading to schizophrenia and other psychiatric disorders in VCFS.

Following the application of two-color fluorescence in-situ hybridization (FISH) to human interphase cells, we examined the replication timing of the fragile-X locus relative to the non-transcribed late replicating alpha-satellite region of chromosome-X, a built-in intracellular reference locus. In this assay, an unreplicated locus is identified by a single hybridization signal (singlet; S), whereas a replicated locus is identified by a duplicated signal (doublet; D). Hence, following simultaneous hybridization with the FMR1 and alpha-satellite probes, male cells with one singlet and one doublet signal per cell (SD cells) indicate S-phase cells where only one of the two loci has replicated. The studied cell samples (lymphocytes and amniocytes) were derived from normal males, fragile-X male patients, and premutation male carriers. Three distinct populations of SD cells were identified among the various samples. The first population had a high frequency of cells showing a doublet FMR1; this pattern, indicating early replication of FMR1, characterized the SD cell population of normal males. The second population had a high frequency of cells showing a singlet FMR1; this pattern, indicating very late replication of FMR1, characterized the SD population of fragile-X patients. The third population had about one half of the cells showing a singlet FMR1 and the other half with a doublet FMR1, indicating somatic variation in the replication timing of FMR1; this pattern was seen in the SD cell population of premutation carriers. The replication status of the FMR1 locus in the cells of patients was altered from late to early in the presence of 5-azadeoxycytidine, an activator of various silent genes. Based on the vast amount of information showing that expressed loci replicate early, whereas unexpressed loci replicate late, we inferred from the replication status of the FMR1 locus that: (1) the normal FMR1 allele is transcriptionally active in lymphocytes and amniocytes; (2) the fully mutated FMR1 allele is transcriptionally silent; (3) the transcriptional activity of the premutated allele is somewhat disturbed; (4) 5-azadeoxycytidine activates the fully mutated FMR1 allele.