RESUMEN
We report on a Mexican mestizo with a multisystemic syndrome including neurological involvement and a type I serum transferrin isoelectric focusing (Tf IEF) pattern. Diagnosis of PMM2-CDG was obtained by clinical exome sequencing (CES) that revealed compound heterozygous variants in PMM2, the encoding gene for the phosphomannomutase 2 (PMM2). This enzyme catalyzes the conversion of mannose-6-P to mannose-1-P required for the synthesis of GDP-Man and Dol-P-Man, donor substrates for glycosylation reactions. The identified variants were c.422G>A (R141H) and c.178G>T, the former being the most frequent PMM2 pathogenic mutation and the latter a previously uncharacterized variant restricted to the Latino population with conflicting interpretations of pathogenicity and that we here report causes leaky non-functional alternative splicing (p.V60Cfs*3).
RESUMEN
The pathogenicity of the opportunistic human fungal pathogen Candida albicans depends on its ability to escape destruction by the host immune system. Using mutant strains that are defective in cell surface glycosylation, cell wall protein synthesis, and yeast-hypha morphogenesis, we have investigated three important aspects of C. albicans innate immune interactions: phagocytosis by primary macrophages and macrophage cell lines, hyphal formation within macrophage phagosomes, and the ability to escape from and kill macrophages. We show that cell wall glycosylation is critically important for the recognition and ingestion of C. albicans by macrophages. Phagocytosis was significantly reduced for mutants deficient in phosphomannan biosynthesis (mmn4Delta, pmr1Delta, and mnt3 mnt5Delta), whereas O- and N-linked mannan defects (mnt1Delta mnt2Delta and mns1Delta) were associated with increased ingestion, compared to the parent wild-type strains and genetically complemented controls. In contrast, macrophage uptake of mutants deficient in cell wall proteins such as adhesins (ece1Delta, hwp1Delta, and als3Delta) and yeast-locked mutants (clb2Delta, hgc1Delta, cph1Delta, efg1Delta, and efg1Delta cph1Delta), was similar to that observed for wild-type C. albicans. Killing of macrophages was abrogated in hypha-deficient strains, significantly reduced in all glycosylation mutants, and comparable to wild type in cell wall protein mutants. The diminished ability of glycosylation mutants to kill macrophages was not a consequence of impaired hyphal formation within macrophage phagosomes. Therefore, cell wall composition and the ability to undergo yeast-hypha morphogenesis are critical determinants of the macrophage's ability to ingest and process C. albicans.
