There are two major categories of peroxisomal disorders (PDs): peroxisomal biogenesis disorders (PBDs) due to defects in peroxisomal (PEX) genes and deficiency of other peroxisomal enzymes (such as D-bifunctional enzyme deficiency due to HSD17B4). PDs are characterized by abnormal elevations of very-long-chain fatty acids (VLCFA). We aimed to evaluate the clinical phenotype of adrenal insufficiency in patients with PD and to assess any genotype-phenotype correlations with adrenal insufficiency. We performed a retrospective electronic medical record review at a single university medical center, of data over 12 years and identified 7 patients with PD. Of the 7 patients identified, 6 patients had a diagnosis of PBD and one had a single peroxisomal enzyme deficiency, HSD17B4. The average age of the patients at diagnosis were 0.61 ± 0.66 years. Four patients (66.7%) had primary adrenal insufficiency: 3, out of the 4, patients had elevated baseline ACTH. Three patients failed to have increased response after the Cortrosyn™ stimulation test. Three patients were on daily hydrocortisone replacement, and 1 patient was on stress-dose hydrocortisone only as needed. Specific genetic variant analysis revealed that all the 3 patients with PBD and adrenal insufficiency who were on steroid supplementation had the compound heterozygous pathogenic variant in exon 13 of PEX1 c.2097dupT (p.Ile700Tyrfs*42) and c.2528G>A (p.Gly843Asp), while the 1 patient with peroxisomal enzyme deficiency and adrenal insufficiency had compound heterozygous pathogenic variants in HSD17B4 c.1369A>T (p.Asn457Tyr) and c.1210 - 1G>A (splice acceptor). Two of these patients with PEX1 variants also required mineralocorticoid supplementation. The 3 PBD patients without adrenal insufficiency did not have a PEX1 variant. Primary adrenal insufficiency is common in patients with PD. Based on our data, patients with the compound heterozygous PEX1 pathogenic variants of exon 13 (c.2097dupT and c.2528G>A) tend to have adrenal insufficiency. Aldosterone deficiency, though rare, can occur in PD.

Peroxisomes are essential organelles for the specialized oxidation of a wide variety of fatty acids, but they are also able to degrade fatty acids that are typically handled by mitochondria. Using a combination of pharmacological inhibition and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein 9 genome editing technology to simultaneously manipulate peroxisomal and mitochondrial fatty acid β-oxidation (FAO) in HEK-293 cells, we identified essential players in the metabolic crosstalk between these organelles. Depletion of carnitine palmitoyltransferase (CPT)2 activity through pharmacological inhibition or knockout (KO) uncovered a significant residual peroxisomal oxidation of lauric and palmitic acid, leading to the production of peroxisomal acylcarnitine intermediates. Generation and analysis of additional single- and double-KO cell lines revealed that the D-bifunctional protein (HSD17B4) and the peroxisomal ABC transporter ABCD3 are essential in peroxisomal oxidation of lauric and palmitic acid. Our results indicate that peroxisomes not only accept acyl-CoAs but can also oxidize acylcarnitines in a similar biochemical pathway. By using an Hsd17b4 KO mouse model, we demonstrated that peroxisomes contribute to the plasma acylcarnitine profile after acute inhibition of CPT2, proving in vivo relevance of this pathway. We summarize that peroxisomal FAO is important when mitochondrial FAO is defective or overloaded.-Violante, S., Achetib, N., van Roermund, C. W. T., Hagen, J., Dodatko, T., Vaz, F. M., Waterham, H. R., Chen, H., Baes, M., Yu, C., Argmann, C. A., Houten, S. M. Peroxisomes can oxidize medium- and long-chain fatty acids through a pathway involving ABCD3 and HSD17B4.