pLoF Variants Research Articles

Replicating the Association of Variants in BSN and APBA1 with Obesity in Diverse Populations.

In a recent study by Zhao et al., rare protein-truncating variants (PTVs) in the BSN and APBA1 genes showed effects on obesity that exceeded those of well-known genes such as MC4R in a UK cohort. In this study, we leveraged the All of Us Research Program, to investigate the association of predicted LoF (pLoF) PTVs in BSN and APBA1 with body mass index (BMI) across a population of diverse ancestry. Our analysis revealed that the impact of pLoF variants in BSN and APBA1 on BMI was notably greater in this cohort, especially among individuals of European ancestry. Additionally, a phenome-wide association study (PheWAS) using the extensive phenotypic data available in the All of Us Research Program uncovered novel associations of BSN and APBA1 heterozygous pLoF carriers with various phenotypes. Specifically, BSN pLoF variants were associated with pulmonary hypertension, atrial fibrillation, and anticoagulant use, while APBA1 pLoF variants were linked to disorders of the temporomandibular joint. These findings underscore the potential of large-scale biobanks in advancing genetic discovery.

The performance of AlphaMissense to identify genes influencing disease

A novel algorithm, AlphaMissense, has been shown to have an improved ability to predict the pathogenicity of rare missense genetic variants. However, it is not known whether AlphaMissense improves the ability of gene-based testing to identify disease-influencing genes. Using whole-exome sequencing data from the UK Biobank, we compared gene-based association analysis strategies including sets of deleterious variants: predicted loss-of-function (pLoF) variants only, pLoF plus AlphaMissense pathogenic variants, pLoF with missense variants predicted to be deleterious by any of five commonly utilized annotation methods (Missense (1/5)) or only variants predicted to be deleterious by all five methods (Missense (5/5)). We measured performance to identify 519 previously identified positive control genes, which can lead to Mendelian diseases, or are the targets of successfully developed medicines. These strategies identified 850k pLoF variants and 5 million deleterious missense variants, including 22k likely pathogenic missense variants identified exclusively by AlphaMissense. The gene-based association tests found 608 significant gene associations (at P<1.25x10-7) across 24 common traits and diseases. Compared to pLoFs plus Missense (5/5), tests using pLoFs and AlphaMissense variants found slightly more significant gene-disease and gene-trait associations, albeit with a marginally lower proportion of positive control genes. Nevertheless, their overall performance was similar. Merging AlphaMissense with Missense (5/5), whether through their intersection or union, did not yield any further enhancement in performance. In summary, employing AlphaMissense to select deleterious variants for gene-based testing did not improve the ability to identify genes that are known to influence disease.

Rare and Common Genetic Variation Underlying Atrial Fibrillation Risk

Atrial fibrillation (AF) has a substantial genetic component. The importance of polygenic risk is well established, while the contribution of rare variants to disease risk warrants characterization in large cohorts. To identify rare predicted loss-of-function (pLOF) variants associated with AF and elucidate their role in risk of AF, cardiomyopathy (CM), and heart failure (HF) in combination with a polygenic risk score (PRS). This was a genetic association and nested case-control study. The impact of rare pLOF variants was evaluated on the risk of incident AF. HF and CM were assessed in cause-specific Cox regressions. End of follow-up was July 1, 2022. Data were analyzed from January to October 2023. The UK Biobank enrolled 502 480 individuals aged 40 to 69 years at inclusion in the United Kingdom between March 13, 2006, and October 1, 2010. UK residents of European ancestry were included. Individuals with prior diagnosis of AF were excluded from analyses of incident AF. Rare pLOF variants and an AF PRS. Risk of AF and incident HF or CM prior to and subsequent to AF diagnosis. A total of 403 990 individuals (218 489 [54.1%] female) with a median (IQR) age of 58 (51-63) years were included; 24 447 were diagnosed with incident AF over a median (IQR) follow-up period of 13.3 (12.4-14.0) years. Rare pLOF variants in 6 genes (TTN, RPL3L, PKP2, CTNNA3, KDM5B, and C10orf71) were associated with AF. Of these, TTN, RPL3L, PKP2, CTNNA3, and KDM5B replicated in an external cohort. Combined with high PRS, rare pLOF variants conferred an odds ratio of 7.08 (95% CI, 6.03-8.28) for AF. Carriers with high PRS also had a substantial 10-year risk of AF (16% in female individuals and 24% in male individuals older than 60 years). Rare pLOF variants were associated with increased risk of CM both prior to AF (hazard ratio [HR], 3.13; 95% CI, 2.24-4.36) and subsequent to AF (HR, 2.98; 95% CI, 1.89-4.69). Rare and common genetic variation were associated with an increased risk of AF. The findings provide insights into the genetic underpinnings of AF and may aid in future genetic risk stratification.

A deep catalogue of protein-coding variation in 983,578 individuals

Rare coding variants that substantially affect function provide insights into the biology of a gene1–3. However, ascertaining the frequency of such variants requires large sample sizes4–8. Here we present a catalogue of human protein-coding variation, derived from exome sequencing of 983,578 individuals across diverse populations. In total, 23% of the Regeneron Genetics Center Million Exome (RGC-ME) data come from individuals of African, East Asian, Indigenous American, Middle Eastern and South Asian ancestry. The catalogue includes more than 10.4 million missense and 1.1 million predicted loss-of-function (pLOF) variants. We identify individuals with rare biallelic pLOF variants in 4,848 genes, 1,751 of which have not been previously reported. From precise quantitative estimates of selection against heterozygous loss of function (LOF), we identify 3,988 LOF-intolerant genes, including 86 that were previously assessed as tolerant and 1,153 that lack established disease annotation. We also define regions of missense depletion at high resolution. Notably, 1,482 genes have regions that are depleted of missense variants despite being tolerant of pLOF variants. Finally, we estimate that 3% of individuals have a clinically actionable genetic variant, and that 11,773 variants reported in ClinVar with unknown significance are likely to be deleterious cryptic splice sites. To facilitate variant interpretation and genetics-informed precision medicine, we make this resource of coding variation from the RGC-ME dataset publicly accessible through a variant allele frequency browser.

Clustering of predicted loss-of-function variants in genes linked with monogenic disease can explain incomplete penetrance

BackgroundGenetic variants that severely alter protein products (e.g. nonsense, frameshift) are often associated with disease. For some genes, these predicted loss-of-function variants (pLoFs) are observed throughout the gene, whilst in others, they occur only at specific locations. We hypothesised that, for genes linked with monogenic diseases that display incomplete penetrance, pLoF variants present in apparently unaffected individuals may be limited to regions where pLoFs are tolerated. To test this, we investigated whether pLoF location could explain instances of incomplete penetrance of variants expected to be pathogenic for Mendelian conditions.MethodsWe used exome sequence data in 454,773 individuals in the UK Biobank (UKB) to investigate the locations of pLoFs in a population cohort. We counted numbers of unique pLoF, missense, and synonymous variants in UKB in each quintile of the coding sequence (CDS) of all protein-coding genes and clustered the variants using Gaussian mixture models. We limited the analyses to genes with ≥ 5 variants of each type (16,473 genes). We compared the locations of pLoFs in UKB with all theoretically possible pLoFs in a transcript, and pathogenic pLoFs from ClinVar, and performed simulations to estimate the false-positive rate of non-uniformly distributed variants.ResultsFor most genes, all variant classes fell into clusters representing broadly uniform variant distributions, but genes in which haploinsufficiency causes developmental disorders were less likely to have uniform pLoF distribution than other genes (P < 2.2 × 10−6). We identified a number of genes, including ARID1B and GATA6, where pLoF variants in the first quarter of the CDS were rescued by the presence of an alternative translation start site and should not be reported as pathogenic. For other genes, such as ODC1, pLoFs were located approximately uniformly across the gene, but pathogenic pLoFs were clustered only at the end, consistent with a gain-of-function disease mechanism.ConclusionsOur results suggest the potential benefits of localised constraint metrics and that the location of pLoF variants should be considered when interpreting variants.

Heterozygous loss-of-function SMC3 variants are associated with variable growth and developmental features

Heterozygous missense variants and in-frame indels in SMC3 are a cause of Cornelia de Lange syndrome (CdLS), marked by intellectual disability, growth deficiency, and dysmorphism, via an apparent dominant-negative mechanism. However, the spectrum of manifestations associated with SMC3 loss-of-function variants has not been reported, leading to hypotheses of alternative phenotypes or even developmental lethality. We used matchmaking servers, patient registries, and other resources to identify individuals with heterozygous, predicted loss-of-function (pLoF) variants in SMC3, and analyzed population databases to characterize mutational intolerance in this gene. Here, we show that SMC3 behaves as an archetypal haploinsufficient gene: it is highly constrained against pLoF variants, strongly depleted for missense variants, and pLoF variants are associated with a range of developmental phenotypes. Among 14 individuals with SMC3 pLoF variants, phenotypes were variable but coalesced on low growth parameters, developmental delay/intellectual disability, and dysmorphism, reminiscent of atypical CdLS. Comparisons to individuals with SMC3 missense/in-frame indel variants demonstrated an overall milder presentation in pLoF carriers. Furthermore, several individuals harboring pLoF variants in SMC3 were nonpenetrant for growth, developmental, and/or dysmorphic features, and some had alternative symptomatologies with rational biological links to SMC3. Analyses of tumor and model system transcriptomic data and epigenetic data in a subset of cases suggest that SMC3 pLoF variants reduce SMC3 expression but do not strongly support clustering with functional genomic signatures of typical CdLS. Our finding of substantial population-scale LoF intolerance in concert with variable growth and developmental features in subjects with SMC3 pLoF variants expands the scope of cohesinopathies, informs on their allelic architecture, and suggests the existence of additional clearly LoF-constrained genes whose disease links will be confirmed only by multi-layered genomic data paired with careful phenotyping.

Abstract 13159: Inverse Relationship Between Genetic Predisposition to Hyper- and Hypo- Cholesterolemia and Incident Type 2 Diabetes

Introduction: High cholesterol and type 2 diabetes mellitus (T2DM) share metabolic and environmental risk factors. Nevertheless, previous literature suggests an inverse association between monogenic/polygenic hypercholesterolemia and T2DM prevalence. We investigated the extent to which polygenic and monogenic hyper- and hypo-cholesterolemia contributes to incident T2DM in a large prospective cohort. Hypothesis: We hypothesized that genetic predisposition to blood cholesterol would associate with incident T2DM risk. Methods: UK Biobank participants who underwent whole-exome sequencing and genome-wide genotyping were included. Based on the Cox proportional hazards model, the associations of familial hypercholesterolemia (FH), polygenic risk scores (PRS) for low-density lipoprotein cholesterol (LDLC), and APOB and PCSK9 predicted loss of function (pLOF) variants with incident T2DM after adjusting for age, sex, genotyping array, lipid-lowering medication use, and the first ten genetic principal components. Results: Among the 443,428 participants, 2,357 (0.56%) had FH and 1,280 (0.30%) had APOB or PCSK9 pLOF variants; the remaining 425,710 (99.13%) were categorized based on LDLC-PRS percentile. Individuals with FH or higher LDLC-PRS had lower risk of incident T2DM. In contrast, individuals with lower LDLC-PRS and APOB and PCSK9 pLOF had an increased risk of T2DM. Conclusions: Monogenic and polygenic risks for increasing and decreasing LDLC were inversely associated with T2DM risk.

Intronic Germline DICER1 Variants in Patients With Sertoli-Leydig Cell Tumor.

Germline pathogenic loss-of-function (pLOF) variants in DICER1 are associated with a predisposition for a variety of solid neoplasms, including pleuropulmonary blastoma and Sertoli-Leydig cell tumor (SLCT). The most common DICER1 pLOF variants include small insertions or deletions leading to frameshifts, and base substitutions leading to nonsense codons or altered splice sites. Larger deletions and pathogenic missense variants occur less frequently. Identifying these variants can trigger surveillance algorithms with potential for early detection of DICER1-related cancers and cascade testing of family members. However, some patients with DICER1-associated tumors have no pLOF variants detected by germline or tumor testing. Here, we present two patients with SLCT whose tumor sequencing showed only a somatic missense DICER1 RNase IIIb variant. Conventional exon-directed germline sequencing revealed no pLOF variants. Using a custom capture panel, we discovered novel intronic variants, ENST00000343455.7: c.1752+213A>G and c.1509+16A>G, that appear to interfere with normal splicing. We suggest that when no DICER1 pLOF variants or large deletions are discovered in exonic regions despite strong clinical suspicion, intron sequencing and splicing analysis should be performed.

Advanced variant classification framework reduces the false positive rate of predicted loss-of-function variants in population sequencing data

Predicted loss of function (pLoF) variants are often highly deleterious and play an important role in disease biology, but many pLoF variants may not result in loss of function (LoF). Here we present a framework that advances interpretation of pLoF variants in research and clinical settings by considering three categories of LoF evasion: (1) predicted rescue by secondary sequence properties, (2) uncertain biological relevance, and (3) potential technical artifacts. We also provide recommendations on adjustments to ACMG/AMP guidelines' PVS1 criterion. Applying this framework to all high-confidence pLoF variants in 22 genes associated with autosomal-recessive disease from the Genome Aggregation Database (gnomAD v.2.1.1) revealed predicted LoF evasion or potential artifacts in 27.3% (304/1,113) of variants. The major reasons were location in the last exon, in a homopolymer repeat, in a low proportion expressed across transcripts (pext) scored region, or the presence of cryptic in-frame splice rescues. Variants predicted to evade LoF or to be potential artifacts were enriched for ClinVar benign variants. PVS1 was downgraded in 99.4% (162/163) of pLoF variants predicted as likely not LoF/not LoF, with 17.2% (28/163) downgraded as a result of our framework, adding to previous guidelines. Variant pathogenicity was affected (mostly from likely pathogenic to VUS) in 20 (71.4%) of these 28 variants. This framework guides assessment of pLoF variants beyond standard annotation pipelines and substantially reduces false positive rates, which is key to ensure accurate LoF variant prediction in both a research and clinical setting.

Association Analyses of Predicted Loss-of-Function Variants Prioritized 15 Genes as Blood Pressure Regulators

BackgroundHypertension, clinically defined by elevated blood pressure (BP), is an important cause of mortality and morbidity worldwide. Many risk factors for hypertension are known, including a positive family history, which suggests that genetics contribute to interindividual BP variation. Genome-wide association studies (GWAS) have identified > 1000 loci associated with BP, yet the identity of the genes responsible for these associations remains largely unknown. MethodsTo pinpoint genes that causally affect variation of BP in humans, we analyzed predicted loss-of-function (pLoF) variants in the UK Biobank whole-exome sequencing dataset (n = 454,709 participants, 6% non-European ancestry). We analyzed genetic associations between systolic or diastolic BP (SBP/DBP) and single pLoF variants (additive and recessive genetic models) as well as with the burden of very rare pLoF variants (minor allele frequency [MAF] < 0.01%). ResultsSingle pLoF variants in 10 genes were associated with BP (ANKDD1B, ENPEP, PNCK, BTN3A2, C1orf145 [OBSCN-AS1], CASP9, DBH, KIAA1161 [MYORG], OR4X1, and TMC3). We also found a burden of rare pLoF variants in 5 additional genes associated with BP (TTN, NOS3, FES, SMAD6, COL21A1). Except for PNCK, which is located on the X-chromosome, these genes map near variants previously associated with BP by GWAS, validating the study of pLoF variants to prioritize causal genes at GWAS loci. ConclusionsOur study highlights 15 genes that likely modulate BP in humans, including 5 genes that harbour pLoF variants associated with lower BP.

Clinical characteristics of heart failure with reduced ejection fraction patients with rare pathogenic variants in dilated cardiomyopathy-associated genes: A subgroup analysis of the PARADIGM-HF trial.

To evaluate the prevalence of pathogenic variants in genes associated with dilated cardiomyopathy (DCM) in a clinical trial population with heart failure and reduced ejection fraction (HFrEF) and describe the baseline characteristics by variant carrier status. This was a post hoc analysis of the Phase 3 PARADIGM-HF trial. Forty-four genes, divided into three tiers, based on definitive, moderate or limited evidence of association with DCM, were assessed for rare predicted loss-of-function (pLoF) variants, which were prioritized using ClinVar annotations, measures of gene transcriptional output and evolutionary constraint, and pLoF confidence predictions. Prevalence was reported for pLoF variant carriers based on DCM-associated gene tiers. Clinical features were compared between carriers and non-carriers. Of the 1412 HFrEF participants with whole-exome sequence data, 68 (4.8%) had at least one pLoF variant in the 8 tier-1 genes (definitive/strong association with DCM), with Titin being most commonly affected. The prevalence increased to 7.5% when considering all 44 genes. Among patients with idiopathic aetiology, 10.0% (23/229) had tier-1 variants only and 12.6% (29/229) had tier-1, -2 or -3 variants. Compared to non-carriers, tier-1 carriers were younger (4 years; adjusted p-value [padj ] = 4 × 10-3 ), leaner (27.8 kg/m2 vs. 29.4 kg/m2 ; padj = 3.2 × 10-3 ), had lower ejection fraction (27.3% vs. 29.8%; padj = 5.8 × 10-3 ), and less likely to have ischaemic aetiology (37.3% vs. 67.4%; padj = 4 × 10-4 ). Deleterious pLoF variants in genes with definitive/strong association with DCM were identified in ∼5% of HFrEF patients from a PARADIGM-HF trial subset, who were younger, had lower ejection fraction and were less likely to have had an ischaemic aetiology.

Rare Heterozygous Loss-of-Function Variants in the Human GLP-1 Receptor Are Not Associated With Cardiometabolic Phenotypes.

Lost glucagon-like peptide 1 receptor (GLP-1R) function affects human physiology. This work aimed to identify coding nonsynonymous GLP1R variants in Danish individuals to link their in vitro phenotypes and clinical phenotypic associations. We sequenced GLP1R in 8642 Danish individuals with type 2 diabetes or normal glucose tolerance and examined the ability of nonsynonymous variants to bind GLP-1 and to signal in transfected cells via cyclic adenosine monophosphate (cAMP) formation and β-arrestin recruitment. We performed a cross-sectional study between the burden of loss-of-signaling (LoS) variants and cardiometabolic phenotypes in 2930 patients with type 2 diabetes and 5712 participants in a population-based cohort. Furthermore, we studied the association between cardiometabolic phenotypes and the burden of the LoS variants and 60 partly overlapping predicted loss-of-function (pLoF) GLP1R variants found in 330 566 unrelated White exome-sequenced participants in the UK Biobank cohort. We identified 36 nonsynonymous variants in GLP1R, of which 10 had a statistically significant loss in GLP-1-induced cAMP signaling compared to wild-type. However, no association was observed between the LoS variants and type 2 diabetes, although LoS variant carriers had a minor increased fasting plasma glucose level. Moreover, pLoF variants from the UK Biobank also did not reveal substantial cardiometabolic associations, despite a small effect on glycated hemoglobin A1c. Since no homozygous LoS nor pLoF variants were identified and heterozygous carriers had similar cardiometabolic phenotype as noncarriers, we conclude that GLP-1R may be of particular importance in human physiology, due to a potential evolutionary intolerance of harmful homozygous GLP1R variants.

Association of HSD17B13 and PNPLA3 With Liver Enzymes and Fibrosis in Hispanic/Latino Individuals of Diverse Genetic Ancestries

Genetic variants affecting liver disease risk vary among racial and ethnic groups. Hispanics/Latinos in the United States have a high prevalence of PNPLA3 I148M, which increases liver disease risk, and a low prevalence of HSD17B13 predicted loss-of-function (pLoF) variants, which reduce risk. Less is known about the prevalence of liver disease-associated variants among Hispanic/Latino subpopulations defined by country of origin and genetic ancestry. We evaluated the prevalence of HSD17B13 pLoF variants and PNPLA3 I148M, and their associations with quantitative liver phenotypes in Hispanic/Latino participants from an electronic health record-linked biobank in New York City. This study included 8739 adult Hispanic/Latino participants of the BioMe biobank with genotyping and exome sequencing data. We estimated the prevalence of Hispanic/Latino individuals harboring HSD17B13 and PNPLA3 variants, stratified by genetic ancestry, and performed association analyses between variants and liver enzymes and Fibrosis-4 (FIB-4) scores. Individuals with ancestry from Ecuador and Mexico had the lowest frequency of HSD17B13 pLoF variants (10%/7%) and the highest frequency of PNPLA3 I148M (54%/65%). These ancestry groups had the highest outpatient alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, and the largest proportion of individuals with a FIB-4 score greater than 2.67. HSD17B13 pLoF variants were associated with reduced ALT level (P= .002), AST level (P< .001), and FIB-4 score (P= .045). PNPLA3 I148M was associated with increased ALT level, AST level, and FIB-4 score (P < .001 for all). HSD17B13 pLoF variants mitigated the increase in ALT conferred by PNPLA3 I148M (P= .006). Variation in HSD17B13 and PNPLA3 variants across genetic ancestry groups may contribute to differential risk for liver fibrosis among Hispanic/Latino individuals.

Exome-wide association analysis of CT imaging-derived hepatic fat in a medical biobank

Nonalcoholic fatty liver disease is common and highly heritable. Genetic studies of hepatic fat have not sufficiently addressed non-European and rare variants. In a medical biobank, we quantitate hepatic fat from clinical computed tomography (CT) scans via deep learning in 10,283 participants with whole-exome sequences available. We conduct exome-wide associations of single variants and rare predicted loss-of-function (pLOF) variants with CT-based hepatic fat and perform cross-modality replication in the UK Biobank (UKB) by linking whole-exome sequences to MRI-based hepatic fat. We confirm single variants previously associated with hepatic fat and identify several additional variants, including two (FGD5 H600Y and CITED2 S198_G199del) that replicated in UKB. A burden of rare pLOF variants in LMF2 is associated with increased hepatic fat and replicates in UKB. Quantitative phenotypes generated from clinical imaging studies and intersected with genomic data in medical biobanks have the potential to identify molecular pathways associated with human traits and disease.

Bi-allelic FRA10AC1 variants in a multisystem human syndrome.

We read the recent article by von Elsner et al.1 with interest. The authors described five individuals from three families with homozygous FRA10AC1 variants, neurodevelopmental delay, intellectual disability, brain abnormalities, microcephaly, growth impairment and craniofacial dysmorphisms. Here, we report findings that support the conclusions reached by von Elsner and colleagues, and provide further insights into this novel disorder. Parents of all participating individuals provided informed consent according to the Declaration of Helsinki and The Central Manchester NHS Research Ethics Committees approved this study (02/CM/238). We ascertained two sisters born to consanguineous parents with global developmental delay, growth impairment, congenital malformations and facial dysmorphism overlapping that of Kabuki syndrome2,3 (OMIM 147920) (Fig. 1A and Table 1). In two affected and one unaffected sibling we performed autozygosity mapping as described previously4 and identified two regions of >2 Mb length that were homozygous only in the affected individuals (Supplementary Table 1). Whole exome sequencing of affected individuals as described previously,5 followed by segregation studies of candidate variants within the linked regions revealed a nonsense FRA10AC1 NM_145246.5:c.328C > T (p.Arg110Ter) variant as the likely cause for the phenotype (Fig. 1B). In gnomAD, there are no homozygous predicted loss of function (pLOF) FRA10AC1 variants, although heterozygous pLOF variants are present at a frequency of ∼1/2000. Next, we identified an individual in the DECIPHER database (257391) with a ∼13 kb homozygous deletion involving a part of FRA10AC1 and no other known gene (Fig. 1A and B). Characterization of the deletion by PCR and Sanger sequencing of genomic DNA (Supplementary material) revealed the variant to be an in-del consisting of a 12 721 bp deletion (Chr10:93 695 674–93 708 393; GRCh38.p12) and a 10 bp duplication. The 5′ breakpoint of the variant was in the intergenic region between FRA10AC1 and LGI1. The 3′ breakpoint was in the intron 4 of FRA10AC1. The duplicated sequence (TTAGTACACA) was a repeat of the first 10 bp of sequence downstream of the variant. The deletion results in loss of the 5′ untranslated region and first four exons of FRA10AC1. Reverse transcription-PCR of RNA extracted from fibroblasts from this patient, revealed absence of FRA10AC1 transcripts (Fig. 1C). Although the individual was ascertained due to her genotype, reverse phenotyping6 revealed her clinical features to overlap significantly with those of the affected individuals in Family 1 (Table 1).1 Collectively, these data provide evidence that bi-allelic pLOF FRA10AC1 variants cause a human developmental disorder.

Clinical Deep Phenotyping of ABCA7 Mutation Carriers.

Background and ObjectivesPutative loss-of-function (pLOF) ABCA7 variants that increase Alzheimer disease (AD) risk were identified; however, deep phenotypic characterization of these variants in mutation carriers is limited. We aimed to obtain deep clinical phenotypes of ABCA7 pLOF mutation carriers from a large retrospectively reviewed series.MethodsGenotypes were determined for 5,353 individuals evaluated at Mayo Clinic for 6 reported ABCA7 pLOF variants (p.E709fs, p.Trp1214X, p.L1403fs, c.4416+2T>G, p.E1679X, and c.5570+5G>C). Medical records of 100 mutation carriers were reviewed for demographics, clinical phenotypes, and diagnoses. Eleven mutation carriers had autopsy-based neuropathologic diagnoses.ResultsWe confirmed that ABCA7 pLOF mutations confer AD risk in our series of 2,495 participants with AD and 2,858 cognitively unaffected participants. Clinical review of 100 mutation carriers demonstrated phenotypic variability of clinical presentations with both memory and nonmemory cognitive impairment and a subset presenting with motor symptoms. There was a wide range of age at onset of cognitive symptoms (ages 56–92 years, mean = 75.6). Ten of the 11 autopsied mutation carriers had AD neuropathology. ABCA7 pLOF mutation carriers had higher rates of depression (41.6%) and first-degree relatives with cognitive impairment (38.1%) compared with the general population.DiscussionOur study provides a deep clinical review of phenotypic characteristics of mutation carriers for 6 ABCA7 pLOF mutations. Although memory impairment was the most common initial symptom, nonmemory cognitive and/or motor symptoms were present in a substantial number of mutation carriers, highlighting the heterogeneity of clinical features associated with these mutations. Likewise, although AD neuropathology is the most common, it is not the only autopsy-based diagnosis. Presence of earlier ages at onset, higher rates of depression, and first-degree relatives with cognitive impairment among mutation carriers suggest that these genetic variants may have more aggressive clinical features than AD in the general population. This deep phenotyping study of ABCA7 pLOF mutation carriers provides essential genotype-phenotype correlations for future precision medicine approaches in the clinical setting.

Effect of Loss-of-Function Genetic Variants in PCSK9 on Glycemic Traits, Neurocognitive Impairment, and Hepatobiliary Function.

To evaluate the association between PCSK9 predicted loss-of-function (pLoF) variants and glycemic traits, hepatobiliary function, and neurocognitive traits. We identified carriers of PCSK9 pLoF variants in UK Biobank exome sequencing data. We assessed the aggregate effects of these variants on lipid and lipoprotein traits, which served as a positive control. Association of PCSK9 pLoF carrier status and glycemic traits, hepatobiliary function, and neurocognitive traits was then evaluated as a measure for adverse effects. We identified 374 individuals carrying one of 41 unique PCSK9 pLoF variants. As expected, we found that PCSK9 pLoF carriers had significantly lower LDL cholesterol C levels (P = 7.4 × 10-55) and apolipoprotein B levels (P = 7.6 × 10-50) than did noncarriers. However, we found no significant associations between pLoF carrier status and glycemic traits, hepatobiliary function, and neurocognitive traits (P > 0.05). Our results do not support adverse effects of PCSK9 pLoF variants on glycemic traits, hepatobiliary function, or neurocognitive traits.

Rare loss-of-function variants in type I IFN immunity genes are not associated with severe COVID-19.

A recent report found that rare predicted loss-of-function (pLOF) variants across 13 candidate genes in TLR3- and IRF7-dependent type I IFN pathways explain up to 3.5% of severe COVID-19 cases. We performed whole-exome or whole-genome sequencing of 1,864 COVID-19 cases (713 with severe and 1,151 with mild disease) and 15,033 ancestry-matched population controls across 4 independent COVID-19 biobanks. We tested whether rare pLOF variants in these 13 genes were associated with severe COVID-19. We identified only 1 rare pLOF mutation across these genes among 713 cases with severe COVID-19 and observed no enrichment of pLOFs in severe cases compared to population controls or mild COVID-19 cases. We found no evidence of association of rare LOF variants in the 13 candidate genes with severe COVID-19 outcomes.

Biased pathogenic assertions of loss of function variants challenge molecular diagnosis of admixed individuals.

Diagnosis of individuals affected by monogenic disorders was significantly improved by next-generation sequencing targeting clinically relevant genes. Whole exomes yield a large number of variants that require several filtering steps, prioritization, and pathogenicity classification. Among the criteria recommended by ACMG, those that rely on population databases critically affect analyses of individuals with underrepresented ancestries. Population-specific allelic frequencies need consideration when characterizing potential deleteriousness of variants. An orthogonal input for classification is annotation of variants previously classified as pathogenic as a criterion that provide supporting evidence widely sourced at ClinVar. We used a whole-genome dataset from a census-based cohort of 1,171 elderly individuals from São Paulo, Brazil, highly admixed, and unaffected by severe monogenic disorders, to investigate if pathogenic assertions in ClinVar are enriched with higher proportions of European ancestry, indicating bias. Potential loss of function (pLOF) variants were filtered from 4,250 genes associated with Mendelian disorders and annotated with ClinVar assertions. Over 1,800 single nucleotide pLOF variants were included, 381 had non-benign assertions. Among carriers (N=463), average European ancestry was significantly higher than noncarriers (N=708; p=.011). pLOFs in genomic contexts of non-European local ancestries were nearly three times less likely to have any ClinVar entry (OR=0.353; p <.0001). Independent pathogenicity assertions are useful for variant classification in molecular diagnosis. However, European overrepresentation of assertions can promote distortions when classifying variants in non-European individuals, even in admixed samples with a relatively high proportion of European ancestry. The investigation and deposit of clinically relevant findings of diverse populations is fundamental improve this scenario.

Racial Disparities Among Clinical Trials for Inherited Forms of Lipodystrophy

Background: There has been renewed interest in understanding how medical research serves minority communities disproportionally affected by disease. A recent study in a predominantly white population identified 12 subjects with partial lipodystrophy by genetics without clinical diagnosis of lipodystrophy (Gonzaga-Jauregui et al., 2020). Partial lipodystrophies are rare monogenic disorders leading to diabetes that can be challenging to diagnosis due to their similarity with common obesity-associated metabolic syndrome. We hypothesize minority populations may be underdiagnosed with lipodystrophy, and thus underrepresented in clinical trials. Methods: We compared racial demographics of lipodystrophic subjects participating in clinical trials to subjects with predicted loss-of-function (pLOF) mutations in 4 genes associated with lipodystrophy in the GnomAD dataset (>140K exome sequences): LMNA & PPARG (causing dominantly inherited partial lipodystrophy), and AGPAT2 & BSCL2 (causing recessively inherited generalized lipodystrophy, which is more phenotypically apparent, as an internal control for the study design). We also compared rates of synonymous mutations in these 4 genes among races to test if subjects of different ethnicities may be more genetically predisposed to developing inherited forms of lipodystrophy. Comparisons were done using chi-square analysis. Results: We identified 322 subjects with pLOF mutations in genes associated with lipodystrophy in the GnomAD dataset. The racial composition of GnomAD subjects with pLOF mutations in each gene was different than GnomAD subjects without pLOF mutations (p<0.001). 144 lipodystrophic subjects with known pathogenic variants in these genes participated in clinical trials. The racial composition of GnomAD and clinical trial subjects with LMNA mutations were significantly different (p=0.024) with the clinical trial cohort being more enriched for white patients (78 vs 21%) and less enriched for Latino patients (7 vs. 21%). There were no differences for other genes. The rates of synonymous mutations were different among patients of different ethnicities, p<0.001 for all genes. Discussion: Partial lipodystrophy due to LMNA mutations may be underdiagnosed in Latinos, leading to reduced participation in clinical trials. The lack of differences in other genes suggests there is no overall cohort bias. Different rates of synonymous mutations suggest there may be evolutionary drivers to racial differences in inherited forms of lipodystrophy, such as founder mutations or heterozygote advantage. Future work will determine prevalence of pLOF variants in lipodystrophy-associated genes in other genetic data sets enriched for minority subjects.