Mizanur Rahman, Rummana Rahim, Abu Hasan
Paroxysmal nocturnal haemoglobinuria (PNH) is a rare stem cell disorder caused by acquired mutation in the X-linked phosphatidylinositol glycan complementation class A gene. The acquired mutation generates a defect in the expression of glycol-phosphatidyl inositol (GPI) linked structures such as the complement regulatory proteins, CD55, CD59, CD24, CD14. A lack of these GPI-linked complement regulatory proteins on red blood cells (RBCs) may cause intravascular complement-mediated haemolysis, resulting in the release of free haemoglobin and leading to the symptoms of PNH. Previous PNH assays have focused on loss of CD55 and CD59 on red cells. However, pathological haemolysis of PNH red cells may generate inaccurate results, as many patients receive erythrocyte transfusions, which may contribute to underestimating the size of the PNH clone population. As a result, PNH erythrocytes may be undetectable even when a substantial PNH population is present. Furthermore, CD55 expression cannot distinguish intermediate complement sensitivity (type II) and more abnormal PNH-type III RBC clones and the sensitivity of CD55 alone is not high enough to detect PNH population sizes of less than 1%. Despite transfusions and anticoagulation management, the survival rate remains low and 35% of cases being fatal within 5 years of diagnosis. Thus, high-sensitivity PNH assays are required to detect PNH populations in order to follow up closely and to provide early treatments for patients. To improve the resolution of PNH detection, we have started PNH assay for the detection of PNH white blood cells (WBCs) with fluorescein-labelled proaerolysin (FLAER) and two GPI-linked markers, namely CD24 for granulocytes and CD14 for monocytes along with PNH RBC cells with CD235a and CD59. We identified PNH clones in 73 (35.96%) cases out of 203 requests in Apollo Hospitals Dhaka. Among these 73 cases 54 PNH clones were found only in WBC and 13 cases were found both in WBC and RBC. PNH Clone size >50% were found in 20 cases and <1% were found in 15 cases. Thus, the addition of FLAER facilitated the improvement and enhancement of sensitivity in PNH clone identification, and may provide a useful tool for pathologists in PNH diagnosis and for monitoring patients at risk of developing classical/haemolytic PNH to enable treatment to be delivered promptly.
Correspondence: Dr. Mizanur Rahman, Department of Molecular Diagnostics, Apollo Hospitals, Dhaka.