Sickle-cell trait and sickle-cell anaemia

Abstract

(1) If sickle-cell trait is regarded as a heterozygous condition (Ss) and sickle-cell anaemia as a homozygous state (SS), then sickle-cell anaemia can only arise as a result of the mating of two heterozygous individuals (Ss x Ss), or the mating of a heterozygous and a homozygous (Ss x SS) or of two homozygous (SS x SS). 1. (2) If this hypothesis is correct, then there should be a greater amount of homozygous sickle-cell anaemia in a population that has a high percentage of the trait than in a population that has a low sickle-cell trait rate. 2. (3) The great prevalence of the sickle-cell trait among certain of the negro tribes of Africa, and the reputed absence of sickle-cell anaemia, means either ( a) that the present accepted genetical hypothesis is lacking in some important particular, or ( b) that the anaemia is far commoner than has so far been reported. 3. (4) Investigations so far carried out in Kenya show that sickle-cell anaemia is far commoner in the negroes of Africa than has so far been reported ; that owing to high infant and/or intrauterine mortality of the homozygous, few survive to the age of puberty.If this work is confirmed, then sickle-cell anaemia should be found in high frequency in new-born babies and/or infants, and should be much rarer in adults. Work is continuing on this question, and if it can be substantiated that this is indeed the case, then death of the homozygous individual must be an important cause of infant mortality, and may be a factor in the production of the small families common in many African tribes. 4. (5) It is possible that sickle-cell disease may not be easy to determine in foetuses on account of the presence of foetal haemoglobin. 5. (6) It has been stated that the presence of sickle-cell disease in an individual is evidence of negro ancestry. A case is reported here of a Greek girl with undoubted sickle-cell anaemia, and in whom negro ancestry and/or illegitimacy could be excluded. 6. (7) It has been stated that an anaemia due to other causes may be grafted on to sickle-cell trait and the combination mistaken for sickle-cell anaemia. This is unlikely to happen if the following are taken into account: 1. (a) The survival time of cells from sickle-cell anaemia transfused into normal individuals is only from 45 to 60 days : cells from sickle-cell trait similarly treated have a nearly normal survival time. 2. (b) That in sickle-cell anaemia 80 per cent. of the cells sickle when the pressure is reduced to 40 to 30 mm. of Hg, whilst in the trait condition 80 per cent. or less of sickling does not take place until the pressure is reduced to 25 to 15 mm. Hg. 3. (c) That sickle-cell anaemia responds to no known treatment. 4. (d) That cells from cases of sickle-cell anaemia when sealed under cover glasses sickle at once and take on bizarre shapes when incubated at 37dg C. developing filamentous processes ;cells from the trait do not commence to sickle for some time after sealing and even after long periods of incubation never take on such bizarre shapes or develop the long filamentous processes.