Prenatal diagnosis of inborn errors in peroxisomal beta-oxidation

Rational diagnostic strategy for Zellweger syndrome spectrum patients

Zellweger syndrome spectrum (ZSS) comprises a clinically and genetically heterogeneous disease entity, which is caused by mutations in any of the 12 different human PEX genes leading to impaired biogenesis of the peroxisome. Patients potentially suffering from ZSS are diagnosed biochemically by measuring elevated levels of very long chain fatty acids, pristanic acid and phytanic acid in plasma and serum and reduced levels of ether phospholipids in erythrocytes. Published reports on diagnostic procedures for ZSS patients are restricted either to biochemical markers or to defined mutations in a subset of PEX genes. Clarification of the primary genetic defect in an affected patient is crucial for genetic counselling, carrier testing or prenatal diagnosis. In this study, we present a rational diagnostic strategy for patients suspected of ZSS. By combining cell biology and molecular genetic methods in an appropriate sequence, we were able to detect the underlying mutation in various PEX genes within adequate time and cost. We applied this method on 90 patients who presented at our institute, Department of Pediatrics and Pediatric Neurology at Georg August University, and detected 174 mutant alleles within six different PEX genes, including two novel deletions and three new missense mutations in PEX6. Furthermore, this strategy will extend our knowledge on genotype-phenotype correlation in various PEX genes. It will contribute to a better understanding of ZSS pathogenesis, allowing the investigation of the effects of diverse mutations on the interaction between PEX proteins and peroxisomal function in vivo.

A novel PEX12 mutation identified as the cause of a peroxisomal biogenesis disorder with mild clinical phenotype, mild biochemical abnormalities in fibroblasts and a mosaic catalase immunofluorescence pattern, even at 40 degrees C

Mutations in 12 different PEX genes can cause a generalized peroxisomal biogenesis disorder with clinical phenotypes ranging from Zellweger syndrome to infantile Refsum disease. To identify the specific PEX gene to be sequenced, complementation analysis is first performed in fibroblasts using catalase immunofluorescence. A patient with a relatively mild phenotype of infantile cholestasis, hypotonia and motor delay had elevated plasma very long-chain fatty acids and bile acid precursors, but fibroblast studies revealed normal or only mildly abnormal peroxisomal parameters and mosaic catalase immunofluorescence. This mosaicism persisted even when the incubation temperature was increased from 37 degrees C to 40 degrees C, a maneuver previously shown to abolish mosaicism by exacerbating peroxisomal dysfunction. As mosaicism precludes complementation analysis, a candidate gene approach was employed. After PEX1 sequencing was unrewarding, PEX12 sequencing revealed homozygosity for a novel c.102A>T (p.R34S) missense mutation affecting a partially conserved residue in the N-terminal region important for localization to peroxisomes. Transfection of patient fibroblasts with wild-type PEX12 cDNA confirmed that a PEX12 defect was the basis for the PBD. Homozygosity for c.102A>T was identified in a second patient of similar ethnic origin also presenting with a mild phenotype. PEX12 is a highly probable candidate gene for direct sequencing in the context of a mild clinical phenotype with mosaicism and minimally abnormal peroxisomal parameters in fibroblasts.

Specific and rapid quantification of 8-iso-prostaglandin F2alpha in urine of healthy humans and patients with Zellweger syndrome by gas chromatography-tandem mass spectrometry

8-iso-Prostaglandin F2alpha (8-iso-PGF2alpha) is currently discussed as a potential index parameter of oxidative stress in vivo. We describe in this article a fully validated gas chromatographic-tandem mass spectrometric method for the quantitative determination of 8-iso-PGF2alpha in human urine. The method is highly specific and requires a single thin-layer chromatographic step for sample purification. Inter- and intraday imprecision were below 8%. Mean inaccuracy was 5.3% for added levels of 8-iso-PGF2alpha up to 2000 pg/ml of urine. We measured highly elevated excretion of 8-iso-PGF2alpha in the urine of children with peroxisomal beta-oxidation deficiency, i.e. Zellweger syndrome, (63.3+/-16.6 ng/mg creatinine) compared to that of healthy children (0.51+/-0.16 ng/mg creatinine) (mean+/-S.D., both n=5). The method could be useful for diagnosing Zellweger syndrome and for investigating the utility of 8-iso-PGF2alpha as a novel marker for oxidative stress in vivo in man.

X linked adrenoleukodystrophy: clinical presentation, diagnosis, and therapy

X linked adrenoleukodystrophy (X-ALD) is an inherited disorder of peroxisomal metabolism, biochemically characterised by accumulation of saturated very long chain fatty acids. Accumulation of these fatty acids is associated with cerebral demyelination, peripheral nerve abnormalities, and adrenocortical and testicular insufficiency. The lowest estimated birth incidence is one per 100,000. At least six phenotypes can be distinguished, of which the two most frequent are childhood cerebral ALD and adrenomyeloneuropathy. The X-ALD gene has been identified, but thus far no relation between genotype and phenotype has been found. Diagnosis is relatively easy and can be confirmed reliably, and prenatal testing is possible in affected families. Several therapeutic options, some with promising perspectives, are available. Neurologists and other physicians seem not to be familiar with the many facets of X-ALD. In this review, the clinical presentation, the relative frequencies of the different phenotypes, and the diagnostic and therapeutic options are presented.

A misdiagnosis of X-linked adrenoleukodystrophy in cultured chorionic villus cells by the measurement of very long chain fatty acids

A case is reported of a male fetus at risk of X-linked adrenoleucodystrophy who showed a normal cultured chorionic villus cell very long chain fatty acid (VLCFA) profile but at birth exhibited grossly abnormal plasma and cultured fibroblast VLCFAs. Maternal contamination or a sample mix-up was excluded by chromosome analysis and analysis of polymorphic markers. This is the second report of a fetus affected with this disorder who showed normal cultured chorionic villus cell VLCFAs. It highlights the importance of a proper audit of all prenatal diagnoses to evaluate method reliability.

Prenatal diagnosis of peroxisomal disorders. Biochemical and immunocytochemical studies on peroxisomes in human amniocytes

Prenatal diagnoses of peroxisomal disorders, including peroxisome-deficient Zellweger syndrome, isolated deficiency of peroxisomal beta-oxidation enzyme and rhizomelic type chondrodysplasia punctata were investigated by means of the lignoceric acid oxidation assay, indirect immunofluorescence staining and pulse-chase experiments, using cultured amniocytes. Assessment of peroxisomal beta-oxidation activity by means of [1-14C]lignoceric acid oxidation is essential for the diagnosis of a single enzyme deficiency of peroxisomal beta-oxidation with detectable enzyme protein. For the diagnosis of Zellweger syndrome, the absence of peroxisomes was readily determined by immunofluorescence staining of only a few amniocytes. Evidence for abnormal processing of 3-ketoacyl-CoA thiolase leads to the diagnosis of rhizomelic chondrodysplasia punctata. All the fetuses were considered to be normal and the neonates were normal. Use of these methods requires only a small number of amniocytes and will facilitate the prenatal diagnosis of peroxisomal disorders.

Postnatal diagnosis of peroxisomal disorders: a biochemical approach

In recent years an increasing number of inherited decreases in man has been identified in which there is an impairment of one or more peroxisomal functions. Sofar 15 different peroxisomal disorders have been identified which can be subdivided into three distinct groups depending upon whether there is a generalized (group A), multiple (group B) or single (group C) loss of peroxisomal functions. In this paper we will briefly describe the functions of peroxisomes in man which are of direct relevance for the peroxisomal disorders known up to now. Based upon the biochemical characteristics of the different peroxisomal disorders, we well describe a straightforward approach for the postnatal identification of patients suspected to suffer from a peroxisomal disorder. Furthermore, a detailed analysis of the biochemical procedures which should be used preferably, is given.