Bile acid intermediates, 3α,7α,12α-trihydroxycholestanoic acid (THCA) and 3α,7α-dihydroxycholestanoic acid (DHCA), are metabolized in peroxisomes. Some peroxisomal disorders (PDs), such as Zellweger spectrum disorder (ZSD), show an accumulation of bile acid intermediates. In particular, ABCD3 deficiency and acyl-CoA-oxidase 2 deficiency are characterized by these metabolite abnormalities. In patients with ZSD, levels of bile acid intermediates can be lowered by a primary bile acid supplementation treatment; therefore, measuring their levels could help evaluate treatment effectiveness. Here, we established a method for the quantitative determination of bile acid intermediates (THCA/DHCA) for differentiating PDs and assessing bile acid treatment. Serum samples, obtained from patients with several forms of ZSD as well as peroxisomal β-oxidation enzyme deficiencies, were deproteinized and analyzed using liquid chromatography-mass spectrometry. Levels of the bile acid intermediates increased significantly in patients with Zellweger syndrome (ZS) and slightly in patients with neonatal adrenoleukodystrophy and infantile Refsum disease (IRD), reflecting the severity of these diseases. One patient with ZS treated with primary bile acids for 6 months showed slightly decreased serum DHCA levels but significantly increased serum THCA levels. One patient with IRD who underwent living-donor liver transplantation showed a rapid decrease in serum THCA and DHCA levels, which remained undetected for 6 years. In all controls, THCA and DHCA levels were below the detection limit. The analytical method developed in this study is useful for diagnosing various PD and validating bile acid treatment. Additionally, it can help predict the prognosis of patients with PD and support treatment strategies.

Peroxisomal acyl-CoA oxidase (ACOX1) deficiency is a rare autosomal recessive single enzyme deficiency characterized by hypotonia, seizures, failure to thrive, developmental delay, and neurological regression starting from approximately 3 years of age. Here, we report two siblings with ACOX1 deficiency born to non-consanguineous Japanese parents. They showed mild global developmental delay from infancy and began to regress at 5 years 10 months and 5 years 6 months of age respectively. They gradually manifested with cerebellar ataxia, dysarthria, pyramidal signs, and dysphasia. Brain MRI revealed T2 high-intensity areas in the cerebellar white matter, bilateral middle cerebellar peduncle, and transverse tracts of the pons, followed by progressive atrophy of these areas. Intriguingly, the ratios of C24:0, C25:0, and C26:0 to C22:0 in plasma, which usually increase in ACOX1 deficiency were within normal ranges in both patients. On the other hand, whole exome sequencing revealed novel compound heterozygous variants in ACOX1: a frameshift variant (c.160delC:p.Leu54Serfs*18) and a missense variant (c.1259 T > C:p.Phe420Ser). The plasma concentration of individual very long chain fatty acids (C24:0, C25:0, and C26:0) was elevated, and we found that peroxisomes in fibroblasts of the patients were larger in size and fewer in number as previously reported in patients with ACOX1 deficiency. Furthermore, the C24:0 β-oxidation activity was dramatically reduced. Our findings suggest that the elevation of individual plasma very long chain fatty acids concentration, genetic analysis including whole exome analysis, and biochemical studies on the patient's fibroblasts should be considered for the correct diagnosis of ACOX1 deficiency.