Compound heterozygous low-density lipoprotein receptor variants causing homozygous of familial hypercholesterolemia in two sisters: a case report

Introduction

Familial hypercholesterolemia (FH) is a severe inherited disorder of lipid metabolism that follows an autosomal dominant pattern. FH is primarily classified into heterozygous FH (HeFH) and homozygous FH (HoFH). Genetic testing studies have shown that approximately 2% of young patients with myocardial infarction have DNA-confirmed FH (1). Notably, HoFH presents with a more severe clinical phenotype. Due to significant deficiencies or dysfunctions in the low-density lipoprotein receptor (LDLR) gene, patients with HoFH exhibit low-density lipoprotein cholesterol (LDL-C) levels that are 4 to 6 times higher than those observed in healthy individuals. If left undiagnosed and untreated, such pronounced hypercholesterolemia substantially increases the risk of premature coronary artery disease, with many patients succumbing to fatal coronary heart disease in their 20s to 30s (2). Family history is an important clue for FH, but the absence of relatives with heart disease does not mean that the patient does not have FH.

Despite the critical nature of FH, clinical awareness remains suboptimal. This under-recognition not only heightens patients’ risk of adverse cardiovascular events but also imposes significant challenges on healthcare systems (3). Consequently, advancing research on the diagnosis and management of FH is of great clinical and public health importance, as HeFH affects approximately 1 in 250–300 individuals worldwide and was associated with markedly elevated LDL-C levels from birth, leading to a substantially increased risk of premature atherosclerotic cardiovascular disease if left untreated (4,5). Enhancing physician awareness can reduce the rates of misdiagnosis and missed diagnosis, thereby improving early detection and management.

In this study, we report two cases of FH-specifically, two sisters-whose initial presentation was characterized by xanthomas. We performed a comprehensive evaluation of five family members, including detailed clinical assessments, laboratory investigations, and genetic analyses (Figure 1). Our aim is to elucidate the genetic characteristics and pathophysiological mechanisms underlying FH and to evaluate effective therapeutic strategies. Through this investigation, we hope to provide clinicians with improved diagnostic and treatment guidelines, thereby contributing to better prognoses for patients with FH. This case report was prepared in accordance with the CARE reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-372/rc).

Figure 1 Timeline of the patient’s diagnosis and treatment process. LDL-C, low-density lipoprotein cholesterol.

Case presentation

On July 4, 2018, two sisters presented to the outpatient department of Jiangxi Provincial Children’s Hospital with early-onset, widespread xanthomas and markedly elevated LDL-C. Based on their clinical features—including multiple cutaneous xanthomas since early childhood (Case 1 since 2011, with corneal arcus; Case 2 since 2015, without corneal arcus), and the presence of disease in both siblings—HoFH was clinically suspected. Formal diagnosis was established after genetic testing and application of recognized diagnostic criteria. All procedures performed in this study were in accordance with the ethical standards of the institutional research committee. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and was approved by the Ethics Committee of Jiangxi Provincial Children’s Hospital (No. JXSETYY-YXKY-20250091). Written informed consent was obtained from the participants’ legal guardians for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Case 1 (elder sister)

Case 1 is a 10-year-9-month-old female who first developed xanthomas on her extremities in 2011. The lesions persisted for 7 years until she presented to the Department of Endocrinology, Genetics and Metabolism at Jiangxi Children’s Hospital on July 4, 2018. Her medical history revealed that in 2011, her family first noted the appearance of yellow, oval-shaped subcutaneous nodules on her elbows and knees, which subsequently extended to her palms and Achilles tendons. In 2017, she underwent laser therapy at a local hospital; however, the lesions recurred shortly thereafter. There was no reported consanguinity or family history of genetic disorders, and her parents were generally healthy.

On admission, the patient’s vital signs were stable and she was alert. Her physical measurements were as follows: weight 32 kg, height 145.8 cm, and blood pressure 116/62 mmHg. Physical examination revealed multiple yellow nodules of varying sizes located on both elbows, the bases of the finger joints, the sacrococcygeal region, and both knees. Additionally, a corneal arcus was observed in both eyes (Figure 2). Laboratory investigations showed a total cholesterol (TC) level of 12.97 mmol/L and an LDL-C level of 9.94 mmol/L.

Figure 2 Xanthomas and corneal arcus in the older sister. (A) Elbow xanthomas; (B) corneal arcus; (C) xanthomas at the bases of the finger joints; (D) sacrococcygeal xanthomas.

Case 2 (younger sister)

Case 2 is a 7-year-9-month-old female who first developed xanthomas on her extremities in 2015. The lesions persisted for 3 years until she presented to the Department of Endocrinology, Genetics and Metabolism at Jiangxi Children’s Hospital on July 4, 2018. Her medical history revealed that in 2015, yellow xanthomas initially appeared on her elbows and gradually extended to her palms and Achilles tendons, manifesting as oval-shaped subcutaneous nodules. In 2017, she underwent laser therapy at a local hospital; however, the lesions recurred post-treatment.

On admission, her physical examination showed a weight of 22 kg, a height of 125.4 cm, and a blood pressure of 100/56 mmHg. Multiple small, bean-sized yellow nodules were observed on her elbows, palms, knees, popliteal fossae, and the dorsum of her feet. Notably, no corneal arcus was detected in either eye (Figure 3). Laboratory tests revealed a TC level of 13.29 mmol/L and an LDL-C level of 6.33 mmol/L.

Figure 3 Yellow xanthomas at various body sites in the younger sister. (A) Elbow xanthomas; (B) foot xanthomas; (C) popliteal fossa xanthomas; (D) knee.

Furthermore, lipid profile assessments of both parents revealed abnormalities, whereas the paternal grandfather’s lipid levels were within normal limits (Table S1). Additional examinations-including electrocardiography, echocardiography, carotid ultrasonography, and abdominal ultrasound (assessing the liver, gallbladder, pancreas, and spleen)-yielded normal findings among the family members. The research team collected 5 mL of venous blood from both sisters and three other family members for further genetic analysis.

Fasting LDL-C was 3.43 mmol/L in the father, 3.37 mmol/L in the mother, and 3.82 mmol/L in the paternal grandfather. The father carried heterozygous LDLR c.1879G>A (p.Ala627Thr), and the mother carried heterozygous LDLR c.1216C>A (p.Arg406Arg), consistent with HeFH. Each scored 10 points on the Dutch Lipid Clinic Network (DLCN) criteria (8 for a pathogenic/likely pathogenic LDLR variant + 2 for having an affected first-degree relative <18 years with LDL-C >95th percentile and/or tendon xanthomas), meeting the definition of “definite FH”. No cutaneous or ocular signs were noted in the parents, and cardiovascular evaluations in all family members were normal.

Genetic analysis

On July 5, 2018, after discussing with the patients’ parents and obtaining informed consent, genetic testing was performed on Cases 1 and 2 as well as on other available family members. Two milliliters of peripheral blood were collected from the patients, their father, mother, and paternal grandfather, using ethylenediaminetetraacetic acid (EDTA) as an anticoagulant. Genomic DNA was then extracted from these samples using the QIAamp DNA Mini Kit (QIAGEN, Hilden, Germany) following the manufacturer’s instructions.

On July 6, 2018, the extracted DNA was sent to a third-party laboratory (Beijing Maikino Company, Beijing, China) for sequencing. Genomic DNA was analyzed by next-generation sequencing (NGS), targeting all exons of the LDLR gene as well as other genes associated with FH (PCSK9, APOB). Detected variants were verified by Sanger sequencing in the probands and their family members (father, mother, and paternal grandfather). Variant interpretation was carried out by Beijing Maikino Company using the Ensembl Variant Effect Predictor (VEP) and SpliceAI algorithms. The sequencing results, obtained on August 2, 2018, revealed two primary genetic variants. The first variant was c.1216C>A, which denotes a substitution at nucleotide position 1216 in the coding region from cytosine (C) to adenine (A). This change results in a synonymous potentially pathogenic variant at amino acid position 406 (p.Arg406Arg). At this locus, the paternal grandfather did not exhibit the potentially pathogenic variant, the mother was heterozygous, and the paternal grandfather was wild type. This variant likely originated from the mother and is suspected to be potentially pathogenic.

The second variant was c.1879G>A, indicating a substitution at nucleotide position 1879 in the coding region from guanine (G) to adenine (A). This potentially pathogenic variant causes an amino acid change at position 627, replacing A with threonine (T) (p.Ala627Thr). In this case, the paternal grandfather was heterozygous for the potentially pathogenic variant, while both the mother and the paternal grandfather were wild type. This variant likely originated from the father and is also considered potentially pathogenic. The corresponding potentially pathogenic variant diagrams are presented in Figure 4. Per ACMG/AMP guidelines (6), the c.1216C>A (p.Arg406Arg) variant was classified as pathogenic (criteria: PP4, PP1, PP3), based on its strong association with the FH phenotype, co-segregation within the family, and SpliceAI prediction of aberrant splicing (delta score =1.00).

Figure 4 Genetic potentially pathogenic variant analysis in LDLR gene of FH sisters. (A) LDLR gene variant site 1 in FH sisters. Gene sequencing nucleotide change: c.1216C>A, leading to the amino acid change p.Arg406Arg, which is a synonymous variant; (B) LDLR gene variant site 2 in FH sisters. Gene sequencing nucleotide change: c.1879G>A, leading to the amino acid change p.Ala627Thr, which is a missense variant. Variant type: heterozygous; pathogenicity: potentially pathogenic; variant origin: father; previously reported: yes. The red arrows indicate the nucleotide variant sites detected in the sequencing chromatograms. FH, familial hypercholesterolemia; LDLR, low-density lipoprotein receptor.

The c.1879G>A (p.Ala627Thr) variant was classified as likely pathogenic (criteria: PP4, PP1, PM1, PP3), supported by its location in a conserved functional domain, absence in population databases, and reported pathogenicity in ClinVar (Variation ID: VCV000003746.29).

Both variants are listed in ClinVar (RCV000237476.1 and VCV000003746.29) as pathogenic/likely pathogenic for FH (https://www.ncbi.nlm.nih.gov/clinvar/variation/3746/).

Sequencing results were reported on August 2, 2018, confirming the diagnosis of HoFH in both sisters.

Detailed genetic testing results for all family members, including ACMG classifications and ClinVar IDs, are summarized in Table S2.

Diagnosis and therapeutic follow-up

Based on the Saimon Broom criteria (7) and considering the patients’ clinical manifestations, laboratory findings, and genetic analysis results, both cases were diagnosed with HoFH. After extensive discussions with the patients’ guardians, lifestyle modifications and dietary interventions were initiated on July 5, 2018, followed by pharmacological treatment starting on September 5, 2018. The treatment regimen comprised once-daily administration of rosuvastatin (10 mg) and ezetimibe (10 mg), which was maintained continuously for 2 years and 3 months until August 2022.

During this period, no new xanthomas were observed, and both carotid ultrasonography and echocardiography yielded normal findings. However, the levels of TC, LDL-C, and apolipoprotein B (ApoB) did not show significant reductions

On September 2, 2022, Case 1 received a single subcutaneous injection of the proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor evolocumab (Repatha) at a dose of 280 mg. Fifteen days post-treatment, the xanthomas had noticeably softened and diminished in size without the appearance of new lesions, and on September 17, 2022, her LDL-C level had decreased to 7.94 mmol/L. Figure 5 illustrates the longitudinal changes in LDL-C levels during follow-up, highlighting the effect of evolocumab in Case 1. In contrast, since Case 2 was under 12 years of age, evolocumab was not administered, and her most recent follow-up revealed that her LDL-C level remained unchanged at 10.00 mmol/L (as illustrated in Tables S3,S4 and Figure 5).

Figure 5 Longitudinal changes in LDL-C levels in the two sisters during follow-up. LDL-C trajectories of the two sisters with HoFH from January 2020 to September 2022, showing the effect of evolocumab in Case 1 (arrow). Data points reflect actual measurement dates; gaps indicate visits without LDL-C data. HoFH, homozygous familial hypercholesterolemia; LDL-C, low-density lipoprotein cholesterol.

Discussion

Recent studies have underscored the central role of variant in the LDLR, PCSK9, and ApoB genes in the pathogenesis of FH. LDLR variants reduce receptor function and impair the clearance of LDL-C (2,8), PCSK9 variants may disrupt receptor recycling, thereby elevating FH risk (9), and ApoB variants are associated with diminished binding efficiency to LDLR, further compromising cholesterol homeostasis (9,10). These insights provide new perspectives for both the diagnosis and management of FH.

Although synonymous variants are traditionally considered benign due to their lack of impact on the amino acid sequence, growing evidence suggests that some may disrupt gene expression through effects on mRNA splicing. For example, a study (11) reported a synonymous substitution (CGG to AGG at codon 406) in exon 9 of the LDLR gene. Even though the variant doesn’t change the amino acid, it creates a cryptic splice site that causes a 31-bp deletion and a premature stop codon, likely triggering nonsense-mediated decay and loss of LDLR function. This underscores the need to assess splicing effects in synonymous variants, especially in genes like LDLR where haploinsufficiency can cause disease. In our study, the synonymous variant identified may similarly influence pre-mRNA splicing. To assess its pathogenicity, we used Ensembl VEP, which identified the variant as rs121908043 and linked it to two FH cases. SpliceAI predicted a strong splicing effect (Acceptor Gain, delta score =1.00), indicating a high likelihood of splice site creation and supporting its clinical relevance, which suggested that the synonymous c.1216C>A variant may disrupt pre-mRNA splicing and contribute to disease, and its co-segregation with the phenotype and rarity in the population support its classification as potentially pathogenic in this FH family.

For pediatric dyslipidemia, especially in cases of familial FH, treatment strategies must be individualized. When LDL-C levels in pediatric FH patients reach or exceed 6.46 mmol/L (250 mg/dL), long-term, multidisciplinary management becomes necessary (12). Studies have demonstrated that the combination of ezetimibe and atorvastatin is well tolerated, with a safety profile comparable to that of atorvastatin alone or placebo (13). However, in HoFH patients, conventional drug therapies often yield only modest reductions in LDL-C and are insufficient to significantly impede the rapid progression of cardiovascular disease (14).

To overcome treatment limitations, novel lipid-lowering therapies like evinacumab and Evolocumab have shown efficacy (15,16). Evinacumab, working independently of LDLR, reduced LDL-C levels by 48.3% in HoFH children in a Phase III trial, despite some treatment-related adverse events (17,18). Phase III study reported Evolocumab, with weekly doses of 420 mg, was well-tolerated and lowered LDL-C by 30% in HoFH patients on stable lipid-lowering therapies, confirming its efficacy as an adjunctive treatment (19-21). In our study, both HoFH patients were promptly initiated on lifestyle modifications and a low-fat diet, combined with daily atorvastatin therapy (10 mg once daily). Regarding dose selection for the initial use of atorvastatin 10 mg in older sisters, starting treatment at a low dose is recommended in accordance with current guidelines for the treatment of lipid control in children. The recommended starting dose is 5–10 mg/day for children 8–9 years of age and 5–20 mg/day for children 10 years of age and older. For children with HoFH, treatment is recommended to begin at 20 mg/day [Food and Drug Administration (FDA) Drug Formulary, 2023; GoodRx Drug Guide]. Given parental concerns about potential side effects, we chose a dose of 10 mg/day for initial treatment. After 6 months, LDL-C levels remained elevated at 9.75 mmol/L, with no significant reduction observed. Consequently, ezetimibe (10 mg once daily) was added to the regimen and continued for an additional 18 months, with follow-up assessments every 3 months. The results revealed that LDL-C levels were 10.15 mmol/L in Case 1 and 10.05 mmol/L in Case 2. Subsequently, Case 1 received an add-on PCSK9 inhibitor (evolocumab), which reduced her LDL-C level to 7.94 mmol/L—a 27.1% decrease from the previous measurement. Due to age restrictions, evolocumab was not administered to Case 2, and her LDL-C levels remained unchanged. These findings suggest that while evolocumab can partially control disease progression in HoFH patients, it may still fall short of achieving optimal LDL-C targets.

For FH patients who respond inadequately to lifestyle and pharmacologic interventions, alternative strategies such as liver transplantation (LT) and lipoprotein apheresis may be considered. Lipoprotein apheresis can reduce LDL-C levels by 57–75% (22). Additionally, the risk of shunt occlusion-owing to normal hematocrit levels in FH patients-necessitates meticulous care (6). After discussing these considerations with the patients’ guardians, lipoprotein apheresis was not pursued in these cases.

In our cases, the two sisters with HoFH exhibited suboptimal responses to lifestyle and conventional drug therapies, prompting their guardians to consider LT as an alternative treatment strategy.

Conclusions

Early diagnosis and intervention are critical due to HoFH’s severe impact on pediatric cardiovascular health. While traditional drugs often fall short, our cases indicate that the PCSK9 inhibitor evolocumab offers some efficacy. This study underscores the critical importance of treatment in HoFH and highlights the necessity for ongoing research into more effective therapeutic strategies. Through this report, we aim to deepen the understanding of HoFH’s complexity and foster the development of improved treatment protocols.

Acknowledgments

We thank the patient and her parents for their cooperation in this study.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-372/rc

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-372/prf

Funding: This work was supported by the Key Project of the Jiangxi Provincial Administration of Traditional Chinese Medicine (project No. 2021Z001).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-372/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional research committee. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and was approved by the Ethics Committee of Jiangxi Provincial Children’s Hospital (No. JXSETYY-YXKY-20250091). Written informed consent was obtained from the participants’ legal guardians for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Gidding SS. Familial Hypercholesterolemia: Now Part of Cardiovascular Disease Genetic Epidemiology Research. J Am Coll Cardiol 2016;67:2590-2. [Crossref] [PubMed]
2. Onorato A, Sturm AC. Heterozygous Familial Hypercholesterolemia. Circulation 2016;133:e587-9. [Crossref] [PubMed]
3. Ai JY, Zhao PC, Zhang W, et al. Research Progress in the Clinical Treatment of Familial Hypercholesterolemia. Curr Med Chem 2024;31:1082-106. [Crossref] [PubMed]
4. Oakes AH, Adusumalli S, Snider CK, et al. Variation in Cardiologist Statin Prescribing by Clinic Appointment Time. J Am Coll Cardiol 2021;77:661-2. [Crossref] [PubMed]
5. Nordestgaard BG, Chapman MJ, Humphries SE, et al. Familial hypercholesterolaemia is underdiagnosed and undertreated in the general population: guidance for clinicians to prevent coronary heart disease: Consensus Statement of the European Atherosclerosis Society. European Heart Journal 2013;34:3478-90. [Crossref] [PubMed]
6. Harada-Shiba M, Arai H, Ishigaki Y, et al. Guidelines for Diagnosis and Treatment of Familial Hypercholesterolemia 2017. J Atheroscler Thromb 2018;25:751-70. [Crossref] [PubMed]
7. Fleming JK, Sullivan RM, Alfego D, et al. A strategy to increase identification of patients with Familial Hypercholesterolemia: Application of the Simon Broome lipid criteria in a large-scale retrospective analysis. Am J Prev Cardiol 2025;21:100930. [Crossref] [PubMed]
8. Soutar AK, Naoumova RP. Mechanisms of disease: genetic causes of familial hypercholesterolemia. Nat Clin Pract Cardiovasc Med 2007;4:214-25. [Crossref] [PubMed]
9. Tomlinson B, Patil NG, Fok M, et al. Role of PCSK9 Inhibitors in Patients with Familial Hypercholesterolemia. Endocrinol Metab (Seoul) 2021;36:279-95. [Crossref] [PubMed]
10. Canepari C, Cantore A. Gene transfer and genome editing for familial hypercholesterolemia. Front Mol Med 2023;3:1140997. [Crossref] [PubMed]
11. Bourbon M, Sun XM, Soutar AK. A rare polymorphism in the low density lipoprotein (LDL) gene that affects mRNA splicing. Atherosclerosis 2007;195:e17-20. [Crossref] [PubMed]
12. Santos RD, Duell PB, East C, et al. Long-term efficacy and safety of mipomersen in patients with familial hypercholesterolaemia: 2-year interim results of an open-label extension. Eur Heart J 2015;36:566-75. [Crossref] [PubMed]
13. Ballantyne CM, Houri J, Notarbartolo A, et al. Effect of ezetimibe coadministered with atorvastatin in 628 patients with primary hypercholesterolemia: a prospective, randomized, double-blind trial. Circulation 2003;107:2409-15. [Crossref] [PubMed]
14. Kasiewicz LN, Biswas S, Beach A, et al. GalNAc-Lipid nanoparticles enable non-LDLR dependent hepatic delivery of a CRISPR base editing therapy. Nat Commun 2023;14:2776. [Crossref] [PubMed]
15. Rosenson RS, Burgess LJ, Ebenbichler CF, et al. Longer-Term Efficacy and Safety of Evinacumab in Patients With Refractory Hypercholesterolemia. JAMA Cardiol 2023;8:1070-6. [Crossref] [PubMed]
16. de Ferranti SD. Evolocumab in Children with Heterozygous Familial Hypercholesterolemia. N Engl J Med 2020;383:1385-6. [Crossref] [PubMed]
17. Raal FJ, Rosenson RS, Reeskamp LF, et al. Evinacumab for Homozygous Familial Hypercholesterolemia. N Engl J Med 2020;383:711-20. [Crossref] [PubMed]
18. Gaudet D, Gipe DA, Pordy R, et al. ANGPTL3 Inhibition in Homozygous Familial Hypercholesterolemia. N Engl J Med 2017;377:296-7. [Crossref] [PubMed]
19. Harada-Shiba M, Ohta T, Ohtake A, et al. Guidance for Pediatric Familial Hypercholesterolemia 2017. J Atheroscler Thromb 2018;25:539-53. [Crossref] [PubMed]
20. Raal FJ, Honarpour N, Blom DJ, et al. Inhibition of PCSK9 with evolocumab in homozygous familial hypercholesterolaemia (TESLA Part B): a randomised, double-blind, placebo-controlled trial. Lancet 2015;385:341-50. [Crossref] [PubMed]
21. Raal FJ, Hovingh GK, Blom D, et al. Long-term treatment with evolocumab added to conventional drug therapy, with or without apheresis, in patients with homozygous familial hypercholesterolaemia: an interim subset analysis of the open-label TAUSSIG study. Lancet Diabetes Endocrinol 2017;5:280-90. [Crossref] [PubMed]
22. Wang A, Richhariya A, Gandra SR, et al. Systematic Review of Low-Density Lipoprotein Cholesterol Apheresis for the Treatment of Familial Hypercholesterolemia. J Am Heart Assoc 2016;5:e003294. [Crossref] [PubMed]