Cerebrotendinous xanthomatosis (CTX), an autosomal recessive lipid-storage disorder with prominent neurological features, was first described by van Bogaert et al. in 1937. A deficiency of the mitochondrial sterol 27-hydroxylase due to mutations in the CYP27 gene (CYP27) blocks the oxidization of cholesterol side chain at the first step in the formation of bile acids. The accumulation of great amount of cholesterol and cholestanol in various tissues, especially in tendons and neural system, leads to the clinical symptoms including dementia, juvenile cataracts, xanthoma, cerebellar syndrome, atherosclerosis and a variety of neurological dysfunctions in CTX subjects. The diagnosis can be made by demonstrating elevated level of cholestanol in the serum and apprearance of xanthoma in tendon. There is a high prevalence of CTX in the Japanese, Sephardim Jewish and Italian populations. Here in this investigation, a one-reported pedigree of three affected individuals with typical characteristics of CTX and a heterozygous paternal carrier in Taiwan were assembled. The first part of the project was to clarify the genetic causes of these CTX patients and to design a series of analytical tests for achieving rapid and correct confirmation of the diagnosis. First, 3¡¦ and 5¡¦-flanking region as well as all 8 introns and 9 exons fragments of CYP27 were amplified from genomic DNA by polymerase chain reaction (PCR) and followed by single strand conformation polymorphism (SSCP) under optimal conditions. The SSCP patterns were identical among CTX subjects, the carrier, and normal controls for all exons except exon 2, implying some kind of mutation may exist on it. Then, direct DNA sequencer analysis was performed on the suspected PCR fragment of exon 2. A new homozygous mutation of one base-pair deletion of cytosine at codon 326 on exon 2 was found in all three CTX subjects in this family. This novel point deletion of cytosine at Pro102 (CCT) would cause a frameshift in mRNA (Pro102 ¡÷Leu) and result in the appearance of a premature termination condon (TGA) to substitute for Val106(GTG). This severe mistake would cause the breakdown in the normal function of sterol 27-hydroxylase and lead to CTX. However, gene analysis could not represent the corresponding functional proteins under various post-translational modifications in complex biological systems. Proteome is the set of expressed protein complement of a genome and proteomic analysis has been widely used in studies of life sciences. The second part of this study is to characterize the pathological mechanism of CTX patients with serum protein profiles and leukocytes isolated from CTX subjects by means of proteomic technologies, including two-dimensional electrophoresis (2-DE) and MALDI-TOF analysis. The results showed that the amount of vinculin, ABP-280, talin and vimentin in leukocytes of CTX patients increased significantly, reflecting the changes in membrane dynamics concerning cholestanol accumulation. The expression of target proteins in CTX patients and control was further confirmed by Western blotting with specific antisera which indicated the same tendency as 2-DE data. This is the first report to integrate both genomic and proteomic concepts for analyzing the possible mechanisms of CTX and information provided by this report should be very helpful for the future studies on CTX.