HSD17B4 and X-linked adrenoleukodystrophy: To overcome these problems, we applied a commercially available kit for targeted metabolomics in a study with patient samples associated with ZSS (PEX1-mutation), X-linked adrenoleukodystrophy (X-ALD, ABCD1-mutation) and, in a very small subgroup, D-bifunctional protein deficiency type III (D-BPIII, HSD17B4-mutation).