Introduction: Obstructive sleep apnea (OSA) is a complex sleep disorder that presents with a range of symptoms, including excessive daytime sleepiness (EDS), postulated to represent a more severe subtype. Despite significant heritability and past GWASs, genetic mechanisms of the disorder remain unclear. Given that EDS often reflects chronic sleep insufficiency and a pro-inflammatory state, we reasoned it may interact with genetic variants to modify risk for OSA. We tested this hypothesis by investigating gene by sleepiness interaction analysis of OSA.

Methods: Whole-genome sequencing data of 11,619 individuals of diverse race and ethnic backgrounds from the NHLBI Trans-Omics for Precision Medicine program was used, with the outcome being Apnea-Hypopnea Index (AHI) and the exposure Epworth Sleepiness Scale (>10: EDS, <=10: non-EDS). GENESIS R package was used to perform 2-stage rank normalization, adjusting for age, sex, BMI, ancestral PCs, cohort, and genetic relatedness, and rescaling residuals to a unit variance, separately in each study/ancestry group. With these residuals, GEM software was used to perform gene-EDS interaction analyses, including 1 df tests of marginal SNP effect and interaction effect of SNPxEDS on AHI, respectively, and 2 df test of joint significance of both. Robust standard errors were used, with a significance threshold of p<5x10-8.

Results: The 1 df test of marginal SNP effect identified one novel locus that mapped to IFRD1, whose overexpression has been associated with sleep restriction, and hypomethylation with narcolepsy. The 1 df test of interaction effect identified two novel loci that mapped to genes MARCHF1 and CCDC3. The 2 df joint test did not reveal additional novel loci. CCDC3 negatively regulates TNF-alpha, a cytokine postulated to be involved in sleep regulation. MARCHF1 promotes NF-KB, whose degree of activation has shown to correlate with OSA severity.

Conclusion: By modeling the modification effect of EDS on OSA we identified 3 novel loci. This approach may be useful in understanding the genetic factors that vary across OSA subtypes. For next steps, we seek to conduct replication analysis using independent imputed samples.

Support: NHLBI, R01HL153814 (H.W.), R35HL135818 (S.R.).

Introduction: Excessive daytime sleepiness is associated with multiple sleep, cardiometabolic, and neuropsychiatric disorders. Previous genome-wide association studies (GWAS) of daytime sleepiness using a single question in European population revealed associations for multiple genes in central nervous pathways. However, findings are still limited and may not be generalizable to other populations. In this study, we performed the first whole-genome sequence (WGS) analyses for Epworth Sleepiness Scale (ESS) in the NHLBI Trans-Omics for Precision Medicine (TOPMed) program.

Methods: This study includes 15,201 individuals of diverse race and ethnic backgrounds from seven cohorts in the TOPMed. We performed GWAS of single common variants (MAF>0.01) and gene-based burden tests of low-frequency and rare functional variants (loss of function and missense; MAF<0.05). We adjusted for age, sex, body mass index (BMI), study, race/ethnicity, and genetic relatedness using linear mixed effects models implemented in the GENESIS R package.

Results: This sample included 43.8% males with a mean age of 54.9 years and BMI 29.6kg/m2, of whom 21.3% were classified with excessive daytime sleepiness (ESS≥10). In single variant test, we identified one novel genomic locus at rs60249969 (on CELF2) significantly associated with ESS (p-value=3.91x10-8). Suggestive significant associations were observed at 5 novel loci that overlapped with PDE7A/DNAJC5B, AHI1/PDE7B, KCNH7, F5, and FBXL17 (p<110-7). In gene-based burden test, we did not identify any gene significantly associated with the ESS after correcting for multiple comparisons (p<210-6). Suggestive significant evidence was observed at OR1A2 (consisting of 41 missense variants; p-value=1.6510-5), an olfactory receptor gene differentially expressed in choroid plexus in the brain implicated in neurodegenerative diseases.

Conclusion: In our investigation of common and rare variant associations with excessive daytime sleepiness as assessed by the ESS, we identified one significant and several suggestive novel loci that mapped to genes highly expressed in brain tissues, which may have implications on sleep wake control system. Our next step will include replication analyses using independent imputed samples.

Support: R01HL153814 (to H.W.), R35HL135818 (to S.R.).

Introduction: Obstructive sleep apnea (OSA) is a common disorder associated with increased risk of cardiovascular diseases and mortality. Recent observational admixture mapping analysis and gene enrichment analysis linked genes and pathways associated with heme metabolism to OSA traits, but the causal contribution is unclear. Iron and heme metabolism is associated with OSA comorbidities and carotid body ventilatory control mechanisms. In this study, we use gene expression data to examine whether iron and heme related pathways have a causal effect on OSA.
Methods: We performed Mendelian randomization (MR) analyses considering the expression level of 15 candidate Gene Ontology pathways as exposures and four OSA traits as outcomes, including the apnea hypopnea index (AHI), and three nocturnal oxygen saturation measurements. In discovery analysis, we performed two-sample MR using local expression trait loci (cis-eQTLs) from the Genotype-Tissue Expression (GTEx) portal and published genome-wide association summary statistics for OSA traits (N>19,000). Significant pathways were then followed-up by one-sample MR using high coverage DNA and RNA sequencing data from the Multi-Ethnic Study of Atherosclerosis generated by the NHLBI Trans-Omics for Precision Medicine (TOPMed) project.
Results: Discovery analysis identified putative causal associations between up-regulated heme biosynthetic process pathway on increased AHI and overnight hypoxemia (minimum P-value=0.018 across OSA traits). These associations were supported in European and Hispanic/Latino Americans but not in African Americans in replication analysis, consistent with prior ancestry-specific associations between a heme-related gene and OSA traits.

Conclusion: This study suggested a causal association between heme biosynthetic processes and OSA severity, suggesting novel biomarkers and possibly treatment targets. Future work is needed to identify the mechanisms for this association and to exclude reverse causality.

Support: This study was supported by Sleep Research Society Foundation Career
Development Award 018-JP-18 to H.W. and NHLBI R35HL135818 to S.R. Molecular data for the TOPMed MESA (phs001416) was supported by NHLBI.