Hereditary stomatocytosis: phenotypical expression of sodium transport and band 7 peptides in 44 cases.

Abstract

The clinical heterogeneity and the role of red cell membrane protein band 7 in membrane transport were studied in 44 patients with hereditary stomatocytosis with normal red cell membrane lipids. These patients were arbitrarily categorized into three phenotypes, based on the extent of sodium influx: hereditary stomatocytosis Type I: with markedly increased Na influx (8.90 +/- 3.39 mmol/lRBC/h); Type II: with moderately increased Na influx (2.10 +/- 0.79) and Type III with normal Na influx (1.31 +/- 0.13). The three groups of patients were compared with normal controls (1.29 +/- 0.14). The extent of anaemia and jaundice was almost identical in the three groups in the presence of nearly the same degree of stomatocytosis (I: 54.8 +/- 10.7%, II: 38.8 +/- 12.8, and III: 40.2 +/- 10.8). Approximately one third of the cases (14/44) with hereditary stomatocytosis showed no overt haemolysis even with marked stomatocytosis. Cell hydration was abnormal in Type I (MCV 119.6 +/- 8.5 fl, MCHC 29.3 +/- 1.8%) but normal in Types II and III (MCV 98.2 +/- 11.7, 94.1 +/- 8.5; MCHC 34.4 +/- 2.1, 34.5 +/- 2.2). These results indicate that there was no correlation between the extent of Na influx and either the degree of stomatocytosis or the extent of overt haemolysis. The role of band 7 in membrane transport was also studied. Three components (30 kD, 28 kD and 26 kD polypeptides) of band 7 were analysed by SDS-PAGE and NEPHGE/SDS-PAGE, and the content of these polypeptides were expressed as the ratio to band 5. The 30 kDa polypeptide in the three groups was nearly identical to that in normal controls (12.3 +/- 4.0), except for non-haemolysing patients in Type II. The 28 kD peptide was also decreased in five out of nine cases of Type II (25.7 +/- 5.6) as compared with normal controls (32.9 +/- 3.6) and cases of Type I (35.8 +/- 2.8) and Type III (32.7 +/- 2.9). No deficiency of this peptide was noted in Type I patients. No correlation was observed between the content of the 28 kD polypeptide and Na influx (r = 0.416), but the 26 kD polypeptide tended to be elevated in cases with overt haemolysis. These results suggest that band 7 may not be essentially involved in the formation of stomatocytic changes, although the presence of subtle defects in band 7 structure and function may not be ruled out. The present findings provide an important starting point to initiate further extensive investigations.