Assay for Sjögren–Larsson Syndrome Based on a Deficiency of Phytol Degradation

Abstract

Sjogren–Larsson syndrome (SLS) is a metabolic disorder characterized by an accumulation of long-chain fatty alcohols in plasma (1)(2). Studies by Rizzo and coworkers (3)(4)(5) have identified the enzyme that is deficient in SLS as fatty aldehyde dehydrogenase (FALDH; EC 1.2.1.3), which is encoded by the ALDH10 gene. FALDH is part of the microsomal alcohol NAD+-oxidoreductase complex, which functions in the conversion of long-chain fatty alcohols into fatty acids (3). A deficiency of FALDH leads to the accumulation of fatty alcohols in plasma (4)(5). Interestingly, FALDH also plays a role in the degradation of leukotriene B4 (6). In our laboratory, we recently established that SLS patients are also deficient in the degradation of phytol (3,7,11,15-tetramethylhexadec-2-en-1-ol), a branched-chain fatty alcohol commonly found in nature as part of the chlorophyll molecule (7). Interest in phytol has focused mainly on its metabolism to phytanic acid, a fatty acid that plays an important role in Refsum disease and several other peroxisomal diseases (8)(9). However, very little was known about the precise mechanism of the conversion of phytol to phytanic acid until our discovery of the involvement of FALDH in this pathway. Indeed, when we incubated fibroblasts derived from SLS patients in the presence of phytol in the culture medium, we observed a marked deficiency in the conversion of phytol to phytenic acid (Fig. 1A⇓ ). In an effort to confirm this finding, we set up an assay in which fibroblast homogenates were incubated with phytol in the presence of NAD+ and assessed activity by quantifying the amount of phytenic acid formed in this reaction by gas chromatography–mass spectrometry (GC-MS) (7). This assay was both sensitive and reliable for the diagnosis of SLS patients, which is of interest because …