To the Editor: The global burden of premature coronary artery disease (CAD) is increasing among the young population. Premature CAD generally refers to the occurrence of obstructive coronary atherothrombotic lesions in men and women aged <55 years and <65 years, respectively, and particularly in those aged <45 years.[1] The incidence of CAD in the younger population has remained stable or has increased, despite the declining incidence in older adults. Patients with premature CAD have a poor long-term prognosis, experiencing a high rate of recurrent ischemic events, rapid progression to multivessel disease, and frequent premature death.[1] Thus, it is crucial to identify the underlying causes of premature CAD that are distinct from those of age-related CAD and improve patient outcomes through precise diagnosis and treatment.

Several rare monogenic diseases can cause premature CAD; however, the spectrum and frequency of rare genetic diseases in patients with premature CAD remain unclear. Despite being the most widely recognized monogenic cause of premature CAD, familial hypercholesterolemia (FH) remains severely underdiagnosed and undertreated.[2] Other rare monogenic diseases leading to an increased risk of premature atherosclerosis and CAD include lipid metabolism disorders, vascular wall dysfunctions, coagulation, thrombosis disorders, and accelerated aging. However, for most of these rare monogenic diseases besides FH, no clear clinical guidelines have been established for their differentiation and diagnosis in patients with premature CAD. Therefore, the underrecognition of rare genetic causes of premature CAD may hinder opportunities to improve patient outcomes through precision interventions.

In this study, we investigated the spectrum and frequencies of rare monogenic diseases in a cohort of Chinese patients with premature CAD recruited from our center using whole-exome sequencing (WES), an efficient tool for identifying rare pathogenic variations. Furthermore, we aimed to identify the subset of patients with premature CAD that may benefit the most from WES for precision disease management.

This retrospective case series study was conducted at the Peking Union Medical College Hospital (PUMCH) and enrolled patients who underwent coronary angiography (CAG) and were diagnosed with premature CAD in Department of Cardiology from August 2012 to April 2019. The inclusion criteria were as follows: CAD diagnosis during hospitalization with at least one major coronary vessel stenosis >50% or percutaneous coronary intervention; age <45 years (for male) and <50 years (for female) at the time of initial CAD diagnosis; signed informed consent and agreement to provide blood samples. The exclusion criteria were as follows: systemic and chronic inflammatory diseases known to increase the risk of CAD, including rheumatic and autoimmune diseases, chronic kidney disease, chronic infectious diseases, and malignancy; history of glucocorticoid use. The clinical data were extracted from electronic health records (EHR). Blood samples were used for WES and subsequent genetic analyses. All procedures were approved by the Ethics Committee at PUMCH (No. JS-2058) and in accordance with the Declaration of Helsinki. Informed consent was obtained from all participants. Definitions and diagnostic criteria for clinical data, laboratory methods for WES, variant annotation and screening, and descriptions of the statistical analysis are listed in Supplementary Methods, https://links.lww.com/CM9/B879.

In total, 102 patients with premature CAD were eligible to be included in this study [Supplementary Figure 1, https://links.lww.com/CM9/B879]. Their baseline demographic information, clinical history, angiographic data, and laboratory examination are presented in Supplementary Tables 1–3, https://links.lww.com/CM9/B879. Most patients were male (85.2%, 87/102) and median age at the time of CAD diagnosis were of 40 (male) and 45 (female) years. Patients typically presented with acute coronary syndrome and common cardiovascular risk factors, including dyslipidemia, obesity, hypertension (HTN), diabetes, metabolic syndrome (MS), smoking, and a family history of cardiometabolic diseases.

Variant screening after WES was conducted in two steps: targeted screening from a predefined gene panel of monogenic CAD based on the previous literatures [Supplementary Table 4, https://links.lww.com/CM9/B879], followed by exome-wide screening for additional variants. Target panel screening initially identified 191 rare variants in 24 monogenic CAD genes, from which 59 variants in 17 genes met the screening criteria for rare candidate variants that may affect risks of premature CAD [Supplementary Methods, Supplementary Figure 2, and Supplementary Table 5, https://links.lww.com/CM9/B879]. These genes were associated with FH, hypertriglyceridemia, MS, high-density lipoprotein metabolism disorders, arterial calcification, and hyperhomocysteinemia. Subsequently, exome-wide screening identified 34 rare candidate variants among 28 genes that were not included in the target panel [Supplementary Table 6, https://links.lww.com/CM9/B879]. These additional genes have been implicated in inherited diseases such as HTN; cholesterol, triglyceride, and glucose metabolism; vascular wall dysfunctions; and other coexisting monogenic disorders [Supplementary Table 7, https://links.lww.com/CM9/B879]. Approximately, two-thirds of the patients with premature CAD carried at least one rare candidate variant and one-fourth harbored multiple variants [Supplementary Figure 3, https://links.lww.com/CM9/B879]. No significant differences between the clinical characteristics of patients with and without rare candidate variants were observed [Supplementary Table 8, https://links.lww.com/CM9/B879].

Among the 102 patients with premature CAD, nine had positive genetic diagnoses (8.8%) and carried pathogenic, likely pathogenic (P/LP) variants of atherosclerotic, metabolic, or vascular diseases known to increase the risk of premature CAD [Table 1]. Five patients (4.9%) carried P/LP variants in the classical FH genes (LDLR and APOB) and were characterized by typical FH phenotypes, including early CAD onset, higher levels of low-density lipoprotein cholesterol (LDL-C), apolipoprotein B, lipoprotein(a), and modified Dutch Lipid Consensus Network scores, compared to the other patients [Supplementary Table 9, https://links.lww.com/CM9/B879]. Another patient with elevated serum cholesterol carried a pathogenic variant of ABCG5, which has been identified in patients with sitosterolemia and hypercholesterolemia. In addition to monogenic hypercholesterolemia, monogenic causes of MS were identified in two patients, including autosomal dominant CAD type 2 caused by LRP6 mutation and familial partial lipodystrophy type 4 caused by PLIN1 mutation. Both patients showed a severe form of MS, lower blood cholesterol levels, and relatively late CAD onset compared to patients with FH. Finally, another patient had a positive genetic diagnosis of pseudoxanthoma elasticum, a vascular disease caused by ABCC6 pathogenic variants that lead to premature CAD through coronary calcification or stiff coronary stenosis. The patient presented with severe coronary stenosis with calcified and non-calcified coronary plaques on CAG. Most rare genetic diseases identified, except for autosomal dominant CAD caused by LRP6 mutation, currently have specific treatment strategies [Table 1]. Therefore, eight of the nine patients with positive diagnoses may benefit from WES through precision disease management. Multivariate logistic regression revealed that elevated LDL-C levels (defined as >3.4 mmol/L in the Chinese population) were significantly and independently associated with positive genetic diagnosis using WES after adjusting for sex, region of birth, and other cardiometabolic risk factors (odds ratio, 7.160; 95% confidence interval [CI], 1.430–35.843; P = 0.017) [Supplementary Table 10, https://links.lww.com/CM9/B879].

Table 1 - Information of nine patients with positive genetic diagnoses of premature CAD†. Patients (Age [years]/sex) CAD Gene cDNA change Protein change ACMG class Disease Precision managements Classical FH in premature CAD 41/F STEMI LDLR c.1448G>A p.Trp483* P FH Intensive cholesterol-reducing therapies (high-potency statins, ezetimibe, and PCSK9 inhibitors), cascade screening in first-degree relatives 39/M NSTEMI LDLR c.1529C>T p.Thr510Met LP FH 39/M UA LDLR c.1747C>T p.His583Tyr LP FH 35/M STEMI APOB c.10579C>T p.Arg3527Trp P FH 38/M UA APOB c.10579C>T p.Arg3527Trp P FH Other monogenic diseases in premature CAD 36/F UA ABCG5 c.1166G>A p.Arg389His P Sitostero lemia Dietary restriction on plant sterol; Ezetimibe 44/M AMI LRP6 c.1252T>C p.Tyr418His LP ADCAD2 NA 44/M CCS PLIN1 c.598+1G>T p.? LP FPLD4 Metreleptin[4] 41/M NSTEMI ABCC6 c.2542delA p.Met848fs P PXE Etidronate[5] †Complete information on the variants is provided in Supplementary Tables 5 and 6, https://links.lww.com/CM9/B879, and clinical information is provided in Supplementary Tables 11, https://links.lww.com/CM9/B879. *Premature stop codon. p.? a symbol used to indicate uncertainty about the effect of the splicing variant on the protein level. ACMG: American College of Medical Genetics and Genomics; ADCAD2: Autosomal dominant coronary artery disease, type 2; AMI: Acute myocardial infarction; CAD: Coronary artery disease; CCS: Chronic coronary syndromes; F: Female; FH: Familial hypercholesterolemia; FPLD4: Familial partial lipodystrophy, type 4; LP: Likely pathogenic; M: Male; NA: Not available; NSTEMI: Non-ST-segment elevation myocardial infarction; P: Pathogenic; PXE: Pseudoxanthoma elasticum; STEMI: ST-segment elevation myocardial infarction; UA: Unstable angina.

In addition to a positive genetic diagnosis, 25 patients with suspected genetic diagnosis harbored additional rare candidate variants of unknown significance (VUSs) and presented with at least one classical phenotype of genetic diseases other than CAD. This indicated the presence of a wide spectrum of underlying inherited diseases [Supplementary Figures 4 and 5, https://links.lww.com/CM9/B879], including inherited hypercholesterolemia (n = 11; 10.8%), metabolic diseases (n = 16; 15.7%), and vascular wall dysfunction (n = 5; 4.9%). Furthermore, incidental findings of other coexisting Mendelian diseases that may have novel or uncommon associations with premature CAD were identified (n = 5; 4.9%). Besides, 27 patients harbored candidate VUSs but did not present with disease phenotypes (clinically uncorrelated genetic findings), and the remaining 36 patients had negative genetic screening results. Detailed information on 39 patients with clinically correlated genetic findings (positive or suspected genetic diagnoses and incidental findings) is presented in Supplementary Table 11, https://links.lww.com/CM9/B879.

In this case series study, we summarized the spectrum and frequencies of rare genetic diseases detected using WES in Chinese patients with premature CAD. Results revealed that rare monogenic diseases constituted 8.8% of the premature CAD cohort without a clinical history of systemic inflammatory diseases. The spectrum of monogenic causes mainly included inherited hypercholesterolemia, followed by monogenic metabolic and vascular disorders. Elevated LDL-C (>3.4 mmol/L) in patients with premature CAD predicted a higher possibility of positive genetic findings. Most patients with positive genetic diagnoses of premature CAD may benefit from precision disease management.

This study highlights the importance of differential diagnosis in CAD, which can be driven by rare genetic diseases with distinct management strategies detectable by WES, especially for those other than FH. For example, we identified rare monogenic causes of common metabolic disorders in patients with premature CAD. The contribution of rare genetic variations to cardiometabolic diseases and traits was also highlighted in a recent study.[3] Novel treatment strategies for rare monogenic diseases such as metreleptin for the treatment of familial partial lipodystrophy[4] and etidronate for the management of pseudoxanthoma elasticum[5] have also emerged in recent years. With increasing discoveries of rare monogenic diseases underlying premature CAD, precision molecular diagnosis and treatment will open up new opportunities that ultimately benefit patients.

However, a more comprehensive understanding of the spectrum and frequency of rare monogenic diseases in premature CAD population still requires further research in larger samples. Besides, interpreting the VUS findings from WES also poses a clinical challenge owing to the uncertain pathogenicity of these variants. These unresolved issues call for future research to explore the potential of molecular classification and precision management in patients with premature CAD.

Acknowledgment

The authors appreciated all participating patients, as well as the support from Clinical Biobank, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences for the storage of blood samples of patients, and the Clinical Genome Center of KingMed Diagnostics for providing the exome sequencing platform.

Funding

This work was supported by grants from the National Key Research and Development Program of China (Nos. 2022YFC2703100, 2020YFC0861000, and 2016YFC0901500), National Natural Science Foundation (No. 82170486), Beijing Natural Science Foundation (No. L202046), CAMS Innovation Fund for Medical Sciences (Nos. 2021-I2M-1-003 and 2017-I2M-2-001), and Center for Rare Diseases Research, Chinese Academy of Medical Sciences, Beijing, China.

Conflicts of interest

None.

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