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 °C

Abstract

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 longchain 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°C to 40°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.

Clinical Diagnosis, Biochemical Findings, Genetics and Incidence of Zellweger Syndrome

“…Peroxisomes are involved in many anabolic and catabolic processes, including the β-oxidation of very-long-chain fatty acids (VLCFAs); the synthesis of other lipids, such as plasmalogens; and bile-acid metabolism (9,11). ical suspicion of ZS, the fact that the peroxisomal parameters of blood and urine are initially normal does not exclude ZS, and further testing (including fibroblast culture and/or molecular analyses) should be considered (12,13). The syndrome affects liver function and triggers cardiac anomalies, but the extent of liver dysfunction over time, the incidence of cardiac anomalies, and the overall incidence of the syndrome remain unknown in Turkey.…”

Infantile Refsum Disease: Influence of Dietary Treatment on Plasma Phytanic Acid Levels

“…Biochemical diagnosis of IRD may be challenging in patients with normal or mildly increased plasma VLCFA levels Zeharia et al 2007). Indeed, older individuals were shown to have lower plasma ratios of C24:0/C22:0 and C26:0/C22:0 fatty acids when compared with children under one year (Hall et al 1988).…”

Rational diagnostic strategy for Zellweger syndrome spectrum patients

“…In rare cases, patient fibroblasts display a mosaic pattern of catalase localization, that is, partly in the peroxisome as well as in the cytosol (Figure 2c). 5,18,19 Therefore, immunofluorescence analysis with an antibody against catalase was performed in the fibroblasts of patients whose clinical symptoms indicated ZSS but did not contain mutations in , the patient's DNA from EDTA whole blood sample will be extracted and sequenced for the two most common mutations in the most frequently affected PEX gene, PEX1. If the patient is heterozygotic for one of these two mutations, the entire PEX1 gene will be sequenced.…”

“…Furthermore, diverse reports of mutations in PEX genes show that such a strategy fails to identify critical molecular defects underlying the clinical manifestation in many ZSS patients. 3,5,10,24,25 As the exact knowledge about the pathogenic mutation in the patient provides valuable information, we were interested in strategies that could detect PEX gene defects in every single ZSS patient within a reasonable time and cost. On applying the published PEX Gene Screen Algorithm, the mutation could not be identified in 21% of the screened ZSS patients 11 .…”