Boczek, Nicole J.

ABSTRACT Objective Although fetal sex chromosome complement prediction by prenatal cell‐free DNA (cfDNA) screening is highly accurate, discordance between the cfDNA‐inferred chromosomal sex and phenotypic sex observed via ultrasonography or at birth, that is, “fetal sex discordance”, does rarely occur. Such discordance may be caused by differences in sex development (DSD) or technical or biological artifacts. This study aims to provide insights into the proportion of fetal sex discordance cases caused by DSD versus non‐DSD artifacts. Method We retrospectively reviewed 122,748 cases that underwent diagnostic testing at the Mayo Clinic Cytogenetics Laboratory between 2015 and 2023. Thirty‐three singleton‐gestation cases tested for fetal sex discordances were identified. Results Fetal sex discordance was attributed to non‐DSD artifacts in 24 (73%) of the 33 patients. In these cases, the phenotypic sex matched the chromosomal sex revealed by diagnostic cytogenetic testing. The remaining 9 patients included one with mosaic 46,X,psu idic(Y)(q11.21)/45,X, 5 with 46,XY DSD, and 3 with 46,XX DSD. Conclusion The majority of fetal sex discordance cases are caused by non‐DSD artifacts rather than DSD. Accurate clinical counseling of fetal sex discordance requires distinguishing between DSD and non‐DSD causes, emphasizing the need for diagnostic cytogenetic testing.

AbstractBackgroundMT‐RNR1 variants are a well‐known cause of aminoglycoside‐induced hearing loss (AIHL). Individuals with cystic fibrosis (CF) routinely receive aminoglycosides and are at high risk of AIHL. However, genetic testing before treatment is not routinely performed due to perceived rarity of risk, and cost ineffectiveness with traditional technologies.AimAssess the utility of large‐scale screening for AIHL risk in the CF population, using digital droplet polymerase chain reaction (ddPCR), a novel and scalable low‐cost molecular technique.MethodsUsing a clinically validated ddPCR assay, we performed retrospective testing on 122 and prospective testing on 32 individuals with CF for the two most common pathogenic variants associated with AIHL, MT‐RNR1 m.1555 A > G and m.1494 C > T. Our study screened the largest known cohort of pediatric cases of CF (94/154) for these specific alterations.ResultsWe identified two individuals positive for MT‐RNR1 m.1555 A > G and no positives for m.1494 C > T. Of 32 prospective cases, 17 had aminoglycoside exposure. The positive case in our prospective group recently began inhaled tobramycin and denied hearing issues. The clinician adjusted to care for both the patient and sibling with CF (not included in cohort) who is presumed positive for m.1555 A > G due to the nature of mitochondrial inheritance.ConclusionOur findings demonstrate the utility of pretreatment screening in the cystic fibrosis population for AIHL risk using ddPCR, a scalable and robust testing methodology at a fraction of the cost as compared to other sequencing‐based methods. Therefore, the use of large‐scale screening for AIHL risk in the cystic fibrosis community should be re‐visited.

Background: Mutations in the CACNA1C-encoded L-type calcium channel have been associated with Timothy Syndrome (TS) with severe QT prolongation, cardiac hypertrophy, syndactyly, facial dysmorphisms, developmental delay, and sudden death by impaired channel inactivation and increase peak current. Recently, a small number of patients with CACNA1C mutations with only long QT syndrome (LQTS) have been described. Objective: To explore whether CACNA1C mutations associated with TS were mechanistically and clinically distinct from CACNA1C-mediated LQTS. Methods/Results: Illumina HiSeq 2000 platform-based whole exome sequencing with variant alignment using HGSC Mercury analysis and Atlas2 revealed a novel variant CACNA1C-L762F that co-segregated with affected patients of a large, multi-generational family with LQTS and sudden death. The proband presented at 3 years of age with out-of-hospital cardiac arrest and demonstrated QTc of 530. The mutation localized to the DII/DIII intracellular linker domain of the channel in a highly conserved region in close proximity to the 6th DI transmembrane domain. Whole cell patch clamp of heterologously expressed CACNA1C-L762F in TSA201 cells demonstrated slower inactivation tau and increased late current indicating its gain-of-function cellular electrophysiological phenotype. Comprehensive review and topological mapping of all described CACNA1C mutations associated with TS or LQTS revealed disease-specific hotspots. TS-associated mutations localized to cytoplasmic aspects of transmembrane domains while LQTS-associated mutations localized to cytoplasmic N- and C-terminal domains and linker regions. Probands hosting TS mutations demonstrated markedly prolonged QTc values compared to LQTS (618 vs 486 ms, p<0.001) and were younger at presentation (2.7 vs 20.1 years, p<0.002). Supporting these associations, the L762F mutation localized closer to the CACNA1C transmembrane domain than any other LQTS mutation and are associated with a QTc and age of diagnosis reflective of TS-associated mutations. Conclusions: The CACNA1C-L762F mutation is associated with biochemical and clinical features which highlight a molecular and clinical distinction between TS- and LQTS-associated CACNA1C mutations.

Abstract Motivation Genomic data are prevalent, leading to frequent encounters with uninterpreted variants or mutations with unknown mechanisms of effect. Researchers must manually aggregate data from multiple sources and across related proteins, mentally translating effects between the genome and proteome, to attempt to understand mechanisms. Materials and methods P2T2 presents diverse data and annotation types in a unified protein-centric view, facilitating the interpretation of coding variants and hypothesis generation. Information from primary sequence, domain, motif, and structural levels are presented and also organized into the first Paralog Annotation Analysis across the human proteome. Results Our tool assists research efforts to interpret genomic variation by aggregating diverse, relevant, and proteome-wide information into a unified interactive web-based interface. Additionally, we provide a REST API enabling automated data queries, or repurposing data for other studies. Conclusion The unified protein-centric interface presented in P2T2 will help researchers interpret novel variants identified through next-generation sequencing. Code and server link available at github.com/GenomicInterpretation/p2t2.

Variants in PURA have recently been associated with an autosomal dominant form of PURA-related neurodevelopmental disorders. Using whole exome sequencing, patients with neurological phenotypes including hypotonia, developmental delay, learning disabilities, and seizures were identified to have de novo variants in PURA. We describe a proband with features similar to the previously described cases with PURA variants, but including additional features, such as short stature, delayed bone age, and delayed puberty. Exome sequencing revealed a novel pathogenic nonsense variant, c.190A>T (p.Lys64*; NM_005859), in PURA that was not inherited from the proband’s mother. In the recent literature, a significant number of patients with variants in PURA have been described, but to our knowledge, none of these patients have the delayed bone age and growth plateau observed in the proband. It is therefore possible that the above PURA variant may be responsible for the novel features and thus expands the PURA-related phenotype spectrum.

Abstract Background Deafness and hearing loss are common conditions that can be seen independently or as part of a syndrome and are often mediated by genetic causes. We sought to develop and validate a hereditary hearing loss panel (HHLP) to detect single nucleotide variants (SNVs), insertions and deletions (indels), and copy number variants (CNVs) in 166 genes related to nonsyndromic and syndromic hearing loss. Methods We developed a custom-capture next-generation sequencing (NGS) reagent to detect all coding regions, ±10 flanking bp, for the 166 genes related to nonsyndromic and syndromic hearing loss. Our validation consisted of testing 52 samples to establish accuracy, reproducibility, and analytical sensitivity. In addition to NGS, supplementary methods, including multiplex ligation-dependent probe amplification, long-range PCR, and Sanger sequencing, were used to ensure coverage of regions that had high complexity or homology. Results We observed 100% positive and negative percentage agreement for detection of SNVs (n = 362), small indels (1–22 bp, n = 25), and CNVs (gains, n = 8; losses, n = 17). Finally, we showed that this assay was able to detect variants with a variant allele frequency ≥20% for SNVs and indels and ≥30% to 35% for CNVs. Conclusions We validated an HHLP that detects SNVs, indels, and CNVs in 166 genes related to syndromic and nonsyndromic hearing loss. The results of this assay can be utilized to confirm a diagnosis of hearing loss and related syndromic disorders associated with known causal genes.

Abstract Aims Pathogenic gain-of-function variants in CACAN1C cause type-8 long QT syndrome (LQT8). We sought to describe the electrocardiographic features in LQT8 and utilize molecular modelling to gain mechanistic insights into its genetic culprits. Methods and results Rare variants in CACNA1C were identified from genetic testing laboratories. Treating physicians provided clinical information. Variant pathogenicity was independently assessed according to recent guidelines. Pathogenic (P) and likely pathogenic (LP) variants were mapped onto a 3D modelled structure of the Cav1.2 protein. Nine P/LP variants, identified in 23 patients from 19 families with non-syndromic LQTS were identified. Six variants, found in 79% of families, clustered to a 4-residue section in the cytosolic II–III loop region which forms a region capable of binding STAC SH3 domains. Therefore, variants may affect binding of SH3-domain containing proteins. Arrhythmic events occurred in similar proportions of patients with II–III loop variants and with other P/LP variants (53% vs. 48%, P = 0.41) despite shorter QTc intervals (477 ± 31 ms vs. 515 ± 37 ms, P = 0.03). A history of sudden death was reported only in families with II–III loop variants (60% vs. 0%, P = 0.03). The predominant T-wave morphology was a late peaking T wave with a steep descending limb. Exercise testing demonstrated QTc prolongation on standing and at 4 min recovery after exercise. Conclusion The majority of P/LP variants in patients with CACNA1C-mediated LQT8 cluster in an SH3-binding domain of the cytosolic II–III loop. This represents a ‘mutation hotspot’ in LQT8. A late-peaking T wave with a steep descending limb and QT prolongation on exercise are commonly seen.

Wolf‐Hirschhorn syndrome (WHS) is a microdeletion syndrome characterized by distinctive facial features consisting of “Greek warrior helmet” appearance, prenatal and postnatal growth deficiency, developmental disability, and seizures. This disorder is caused by heterozygous deletions on chromosome 4p16.3 often identified by cytogenetic techniques. Many groups have attempted to identify the critical region within this deletion to establish which genes are responsible for WHS. Herein, clinical whole exome sequencing (WES) was performed on a child with developmental delays, mild facial dysmorphisms, short stature, failure to thrive, and microcephaly, and revealed a de novo frameshift variant, c.1676_1679del (p.Arg559Tfs*38), in WHSC1 (NSD2). While WHSC1 falls within the WHS critical region, individuals with only disruption of this gene have only recently been described in the literature. Loss‐of‐function de novo variations in WHSC1 were identified in large developmental delay, autism, diagnostic, and congenital cardiac cohorts, as well as recent case reports, suggesting that de novo loss‐of‐function WHSC1 variants may be related to disease. These findings, along with our patient suggest that loss‐of‐function variation in WHSC1 may lead to a mild form of Wolf‐Hirschhorn syndrome, and also may suggest that the developmental delays, facial dysmorphisms, and short stature seen in WHS may be due to disruption of WHSC1 gene.