A new test method for biochemical analysis of plasmalogens in dried blood spots and erythrocytes from patients with peroxisomal disorders.

Measurement of plasmalogens is useful for the biochemical diagnosis of rhizomelic chondrodysplasia punctata (RCDP) and is also informative for Zellweger spectrum disorders (ZSD). We have developed a test method for the simultaneous quantitation of C16:0, C18:0, and C018:1 plasmalogen (PG) species and their corresponding fatty acids (FAs) in dried blood spots (DBS) and erythrocytes (RBC) by using capillary gas chromatography-mass spectrometry. Normal reference ranges for measured markers and 10 calculated ratios were established by the analysis of 720 and 473 unaffected DBS and RBC samples, respectively. Determination of preliminary disease ranges was made by using 45 samples from 43 unique patients: RCDP type 1 (DBS: 1 mild, 17 severe; RBC: 1 mild, 6 severe), RCDP type 2 (DBS: 2 mild, 1 severe; RBC: 2 severe), RCDP type 3 (DBS: 1 severe), RCDP type 4 (RBC: 2 severe), and ZSD (DBS: 3 severe; RBC: 2 mild, 7 severe). Postanalytical interpretive tools in Collaborative Laboratory Integrated Reports (CLIR) were used to generate an integrated score and a likelihood of disease. In conjunction with a review of clinical phenotype, phytanic acid, and very long-chain FA test results, the CLIR analysis allowed for differentiation between RCDP and ZSD. Data will continue to be gathered to improve CLIR analysis as more samples from affected patients with variable disease severity are analyzed. The addition of DBS analysis of PGs may allow for at-home specimen collection and second-tier testing for newborn screening programs.