Glycosylphosphatidylinositol biosynthesis deficiency 15 caused by GPAA1 gene mutation: a rare disease study / 中国当代儿科杂志

A boy, aged 6 years, attended the hospital due to global developmental delay for 6 years and recurrent fever and convulsions for 5 years. The boy was found to have delayed mental and motor development at the age of 3 months and experienced recurrent fever and convulsions since the age of 1 year, with intermittent canker sores and purulent tonsillitis. During the fever period, blood tests showed elevated white blood cell count, C-reactive protein, and erythrocyte sedimentation rate, which returned to normal after the fever subsides. Electroencephalography showed epilepsy, and genetic testing showed compound heterozygous mutations in the GPAA1 gene. The boy was finally diagnosed with glycosylphosphatidylinositol biosynthesis deficiency 15 (GPIBD15) and periodic fever. The patient did not respond well to antiepileptic treatment, but showed successful fever control with glucocorticoid therapy. This article reports the first case of GPIBD15 caused by GPAA1 gene mutation in China and summarizes the genetic features, clinical features, diagnosis, and treatment of this disease, which provides a reference for the early diagnosis and treatment of GPIBD15.

Hemoglobinúria paroxística noturna: da fisiopatologia ao tratamento / Paroxysmal nocturnal hemoglobinuria: from physiopathology to treatment

Hemoglobinúria paroxística noturna (HPN) é uma anemia hemolítica crônica adquirida rara, de curso clínico extremamente variável. Apresenta-se frequentemente com infecções recorrentes, neutropenia e trombocitopenia, e surge em associação com outras doenças hematológicas, especialmente com síndromes de falência medular, como anemia aplásica e síndrome mielodisplásica. É considerada ainda um tipo de trombofilia adquirida, apresentando-se com tromboses venosas variadas, com especial predileção por trombose de veias hepáticas e intra-abdominais, sua maior causa de mortalidade. A tríade anemia hemolítica, pancitopenia e trombose faz da HPN uma síndrome clínica única, que deixou de ser encarada como simples anemia hemolítica adquirida para ser considerada um defeito mutacional clonal da célula-tronco hematopoética (CTH). A mutação ocorre no gene da fosfaditilinositolglicana classe-A, e resulta no bloqueio precoce da síntese de âncoras de glicosilfosfaditilinositol (GPI), responsáveis por manter aderidas à membrana plasmática dezenas de proteínas com funções específicas. A falência em sintetizar GPI madura gera redução de todas as proteínas de superfície normalmente ancoradas por ela. Dentre elas estão o CD55 e o CD59, que controlam a ativação da cascata do complemento. Assim, na HPN há aumento da susceptibilidade de eritrócitos ao complemento, gerando hemólise. Revisa-se aqui sua fisiopatologia, curso clínico, os tratamentos disponíveis com ênfase para o transplante de células-tronco hematopoéticas alogênicas e para o eculizumab, um anticorpo monoclonal humanizado que bloqueia a ativação do complemento terminal no nível C5 e previne a formação do complexo de ataque à membrana, a primeira droga a demonstrar eficácia no tratamento da HPN.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder, an acquired chronic hemolytic anemia, often associated with recurrent nocturnal exacerbations, recurrent infections, neutropenia, thrombocytopenia, and episodes of venous thrombosis. Its clinical course is highly variable. It frequently arises in association with bone marrow failure, particularly aplastic anemia and myelodysplastic syndrome. It is also an acquired thrombophilia, presenting with a variety of venous thrombosis, mainly manifested with intra-abdominal thrombosis, here the major cause of mortality. The triad of hemolytic anemia, pancytopenia, and thrombosis makes a truly unique clinical syndrome of PNH, which was reclassified from a purely acquired hemolytic anemia to a hematopoietic stem cell mutation defect of the phosphatidyl inositol glycanclass-A gene. This mutation results in an early block in the synthesis of glycosylphosphatidylinositol (GPI) anchors, responsible for binding membrane functional proteins. Among these proteins are the complement inhibitors, especially CD55 and CD59, that play a key role in protecting blood cells from complement cascade attack. Therefore, in PNH occurs an increased susceptibility of red cells to complement, and consequently, hemolysis. We here review PNH physiopathology, clinical course, and treatment options, especially eculizumab, a humanized monoclonal antibody that blocks the activation of terminal complement at C5 and prevents formation of the terminal complement complex, the first effective drug therapy for PNH.

Screening for glycosylphosphatidylinositol-anchored proteins in the Paracoccidioides brasiliensis transcriptome

Open reading frames in the transcriptome of Paracoccidioides brasiliensis were screened for potential glycosylphosphatidylinositol (GPI)-anchored proteins, which are a functionally and structurally diverse family of post-translationally modified molecules found in a variety of eukaryotic cells. Numerous studies have demonstrated that various GPI anchor sequences can affect the localization of these proteins in the plasma membrane or the cell wall. The GPI anchor core is produced in the endoplasmic reticulum by sequential addition of monosaccharides and phospho-ethanolamine to phosphatidylinositol. The complete GPI anchor is post-translationally attached to the protein carboxyl-terminus by GPI transamidases. Removal of this GPI lipid moiety by phospholipases generates a soluble form of the protein. The identification of putative GPI-attached proteins in the P. brasiliensis transcriptome was based on the following criteria: the presence of an N-terminal signal peptide for secretion and a hydrophobic region in the C-terminus presenting the GPI-attachment site. The proteins that were identified were in several functional categories: i) eight proteins were predicted to be enzymes (Gel1, Gel2, Gel3, alpha-amylase, aspartic proteinase, Cu-Zn SOD, DFG5, PLB); ii) Ag2/PRA, ELI-Ag1 and Gel1 are probably surface antigens; iii) Crh-like and the GPI-anchored cell wall protein have a putative structural role; iv) ECM33 and Gels (1, 2 and 3) are possibly involved in cell wall biosynthesis, and v) extracellular matrix protein is considered to be an adhesion protein. In addition, eight deduced proteins were predicted to localize in the plasma membrane and six in the cell wall. We also identified proteins involved in the synthesis, attachment and cleaving of the GPI anchor in the P. brasiliensis transcriptome.

Expression of Mycobacterium leprae 18-kDa antigen in yeast in a GPI-anchored form

The 18-kDa protein from Mycobacterium leprae is a major target for the immune response in leprosy. We have developed a system to express this antigen in yeast as a fusion protein with the C-terminal region of the yeast membrane protein GAS1, which would render the recombinant protein anchored to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. Cells lacking the GAS1 gene and transformed with the hybrid 18-kDa-GAS1 construct express a polypeptide that reacts with an 18-kDa-specific monoclonal antibody. In addition, these cells react with an alpha-CRD antibody after GPI-PLC treatment. The non-transformed cells are negative. These data indicate that our system may be suitable for the expression of foreign proteins in yeast in a GPI-anchored form