A teenager boy with a novel variant of Sitosterolemia presented with pancytopenia

Putative Pathogenic Variants of ABCG5 and ABCG8 of Sitosterolemia in Patients With Hyper-Low-Density Lipoprotein Cholesterolemia

Objective

Sitosterolemia is a rare autosomal recessive disease caused by the deleterious variants of adenosine 5'-triphosphate (ATP)-binding cassette sub-family G member 5 (ABCG5) or ATP-binding cassette sub-family G member 8 (ABCG8). There are only few data on the pathogenicity of ABCG5 and ABCG8. This study aimed to propose a scheme for determining variant pathogenicity and to catalog the putative pathogenic variants in sitosterolemia.

Methods

This study enrolled 377 consecutive Japanese patients with hyper-low-density lipoprotein cholesterolemia (mean age: 46.5±19.8 years, with 192 men) who have targeted-sequenced data on ABCG5 or ABCG8 (among 21 Mendelian lipid genes for any dyslipidemias) and serum sitosterol levels at Kanazawa University Hospital from 2016 to 2021. Serum sitosterol levels were divided by 0.79 in patients treated with ezetimibe, accounting for the average reduction with this drug. ABCG5 or ABCG8 variants were defined as putative pathogenic if associated with serum sitosterol levels ≥5 µg/mL or homozygous if associated with serum sitosterol levels ≥10 µg/mL.

Results

Twenty-three ABCG5 or ABCG8 variants (16 missense, 2 nonsense, 2 frameshift, 2 deletion, and 1 splice mutation) were identified. Based on our definition, 11 putative pathogenic variants (median sitosterol level: 10.1 [6.5-17.1] µg/mL) were found in 36 individuals and 12 benign variants (median sitosterol: 3.5 [2.5-4.1] µg/mL) in 14 individuals.

Conclusion

The scheme proposed for assessing the pathogenicity of genetic variations (ABCG5 and ABCG8) is useful. Using this scheme, 11 putative pathogenic, and 12 benign variants in ABCG5 or ABCG were classified.

Age-related reference intervals for serum phytosterols in children by gas chromatography-mass spectrometry and its application in diagnosing sitosterolemia

BACKGROUND AND AIMS

Serum phytosterol profiles are essential for the diagnosis and management of sitosterolemia. However, pediatric reference interval (RI) studies are scarce and various mass spectrometry (MS) approaches for phytosterol analysis still face multiple limitations. Therefore, an optimized gas chromatography (GC)-MS assay and age-related RIs in children are both required.

MATERIALS AND METHODS

Cholesterol and phytosterols (sitosterol, campesterol, cholestanol, stigmasterol, and sitostanol) were simultaneously determined by optimized GC-MS and performance was verified by the lower limit of quantification (LLOQ), linearity, precision, recovery, matrix effects, and method comparison. Healthy children (247 males and 263 females) were recruited, sex and age dependence were assessed using quantile regression (2.5th percentile and 97.5th percentile), and RIs were established according to Clinical and Laboratory Standards Association guideline C28-A3. These RIs were validated in 19 patients with sitosterolemia and 23 patients with hypercholesterolemia.

RESULTS

The optimized method shortened the sample processing time by approximately 60 min. Among the five phytosterols, all precision, recoveries (ranging from 89.97% to 104.94%), and relative matrix effects (%CV: ranging from 0.08% to 13.88%) met the specifications. GC-MS showed good agreement with lower cholesterol concentrations compared to conventional enzymatic methods. No significant differences between males and females were observed for all phytosterols, but age dependency was found and age-related RIs were established accordingly. Five phytosterols were significantly higher than RIs in patients with sitosterolemia.

CONCLUSION

We established age-related RIs for five phytosterols in children based on an optimized GC-MS assay, providing a screening tool for the diagnosis of sitosterolemia in children.

Children with Severe Hypercholesterolemia Caused by a Pathogenic Mutation in ABCG5

We herein present a case series of hypercholesterolemia caused by a pathogenic mutation in the ATP-binding cassette sub-family G member 5 (ABCG5). Three unrelated infantile patients who were breastfed and had extremely elevated low-density lipoprotein (LDL) cholesterol levels were referred to our hospital. Their LDL cholesterol levels decreased significantly after weaning. Panel sequencing revealed a pathogenic mutation in ABCG5 in each patient. An 8-year-old girl was also referred due to suspected familial hypercholesterolemia. Panel sequencing revealed a pathogenic mutation in ABCG5. A cholesterol-reduced diet alone significantly reduced the LDL cholesterol levels. Moreover, the administration of ezetimibe was found to be beneficial.