D-bifunctional Protein Deficiency Research Articles

Sensitive analysis of serum 3α, 7α, 12α,24-tetrahydroxy-5β-cholestan-26-oic acid diastereomers using gas chromatography–mass spectrometry and its application in peroxisomal d-bifunctional protein deficiency

The final steps in bile acid biosynthesis take place in peroxisomes and involve oxidative cleavage of the side chain of C27-5beta-cholestanoic acids leading to the formation of the primary bile acids cholic acid and chenodeoxycholic acid. The enoyl-CoA hydratase and beta-hydroxy acyl-CoA dehydrogenase reactions involved in the chain shortening of C27-5beta-cholestanoic acids are catalyzed by the recently identified peroxisomal d-bifunctional protein. Deficiencies of d-bifunctional protein lead, among others, to an accumulation of 3alpha,7alpha,12alpha, 24-tetrahydroxy-5beta-cholest-26-oic acid (varanic acid). The ability to resolve the four C24, C25 diastereomers of varanic acid has, so far, only been carried out on biliary bile acids using p -bromophenacyl derivatives. Here, we describe a sensitive gas chromatography-mass spectrometry (GC/MS) method that enables good separation of the four varanic acid diastereomers by use of 2R-butylester-trimethylsilylether derivatives. This method showed the specific accumulation of (24R,25R)-varanic acid in the serum of a patient with isolated deficiency of the d-3-hydroxy acyl-CoA dehydrogenase part of peroxisomal d-bifunctional protein, whereas this diastereomer was absent in a serum sample from a patient suffering from complete d-bifunctional protein deficiency. In samples from both patients an accumulation of (24S,25S)-varanic acid was observed, most likely due to the action of l-bifunctional protein on Delta24E-THCA-CoA. This GC/MS method is applicable to serum samples, obviating the use of bile fluid, and is a helpful tool in the subclassification of patients with peroxisomal d-bifunctional protein deficiency.

D-3-Hydroxyacyl-CoA Dehydratase/ d-3-Hydroxyacyl-CoA Dehydrogenase Bifunctional Protein Deficiency: A Newly Identified Peroxisomal Disorder

Peroxisomal beta-oxidation proceeds from enoyl-CoA through D-3-hydroxyacyl-CoA to 3-ketoacyl-CoA by the D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxy-acyl-CoA dehydrogenase bifunctional protein (d-bifunctional protein), and the oxidation of bile-acid precursors also has been suggested as being catalyzed by the d-bifunctional protein. Because of the important roles of this protein, we reinvestigated two Japanese patients previously diagnosed as having enoyl-CoA hydratase/L-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (L-bifunctional protein) deficiency, in complementation studies. We found that both the protein and the enzyme activity of the d-bifunctional protein were hardly detectable in these patients but that the active L-bifunctional protein was present. The mRNA level in patient 1 was very low, and, for patient 2, mRNA was of a smaller size. Sequencing analysis of the cDNA revealed a 52-bp deletion in patient 1 and a 237-bp deletion in patient 2. This seems to be the first report of D-bifunctional protein deficiency. Patients previously diagnosed as cases of L-bifunctional protein deficiency probably should be reexamined for a possible d-bifunctional protein deficiency.

Bile acid profiles in a peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein deficiency.

Bile acid profiles in serum, urine and bile from an infant with a peroxisomal D-3-hydroxyacyl-CoA dehydratase/D-3-hydroxyacyl-CoA dehydrogenase bifunctional protein (D-bifunctional protein) deficiency were analyzed by means of gas-liquid chromatography, gas-liquid chromatography-mass spectrometry, and high-performance liquid chromatography. As in such several peroxisomal disorders as Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum disease, the accumulation of C27-bile acid intermediates was also demonstrated in the infant with D-bifunctional protein deficiency, accounting for 74% of the total bile acids in serum, 59% in urine, and 35% in bile. In addition, the major constituents of the C27-bile acids were (24R,25R)- and (24R,25S)-3alpha,7alpha,12alpha,24-tetrahydroxy-5be ta-cholestanoic acids along with small amounts of their 24S counterparts. Since immunoreactive acyl-CoA oxidase, L-bifunctional protein, and thiolase were all present in the liver, the impairment of the oxidative side-chain cleavage in bile acid biosynthesis is considered to be due to the defect of D-bifunctional protein.

Field emission observations of carbon on tantalum: R. Klein and L. B. Leder, J. Chem. Phys., 38 (8), 15 April 1963, 1863–1872

Perrault syndrome is a recessive disorder characterized by ovarian dysgenesis in females, sensorineural deafness in both males and females, and in some patients, neurological manifestations. No genes for Perrault syndrome have heretofore been identified. A small family of mixed European ancestry includes two sisters with well-characterized Perrault syndrome. Whole-exome sequencing of genomic DNA from one of these sisters revealed exactly one gene with two rare functional variants: HSD17B4, which encodes 17β-hydroxysteroid dehydrogenase type 4 (HSD17B4), also known as D-bifunctional protein (DBP). HSD17B4/DBP is a multifunctional peroxisomal enzyme involved in fatty acid β-oxidation and steroid metabolism. Both sisters are compound heterozygotes for HSD17B4 c.650A>G (p.Y217C) (maternal allele) and HSB17B4 c.1704T>A (p.Y568X) (paternal allele). The missense mutation is predicted by structural analysis to destabilize the HSD17B4 dehydrogenase domain. The nonsense mutation leads to very low levels of HSD17B4 transcript. Expression of mutant HSD17B4 protein in a compound heterozygote was severely reduced. Mutations in HSD17B4 are known to cause DBP deficiency, an autosomal-recessive disorder of peroxisomal fatty acid β-oxidation that is generally fatal within the first two years of life. No females with DBP deficiency surviving past puberty have been reported, and ovarian dysgenesis has not previously been associated with this illness. Six other families with Perrault syndrome have wild-type sequences of HSD17B4. These results indicate that Perrault syndrome and DBP deficiency overlap clinically; that Perrault syndrome is genetically heterogeneous; that DBP deficiency may be underdiagnosed; and that whole-exome sequencing can reveal critical genes in small, nonconsanguineous families.