Hereditary diseases are preventable / by Victor Bulyzhenkov and Bernadette Modell

Hereditary diseases are preventable by Victor Bulyzhenkov and Bernadette Modell Hereditary disorders are com-mon, interact with infec-tious and nutritional dis- eases, can often be managed or prevented by relatively simple ap- proaches, and deserve inclusion in family planning and maternal and child health programmes. Common disorders of later life such as coro- nary heart disease, diabetes melli- tus, cancer and mental illness also have important genetic compo- nents. The WHO Hereditary Diseases Programme is concerned with de- veloping community approaches and appropriate technology to pre- vent and control the most common of them. More than two per cent of all in- fants are born with severe heredi- tary disorders. But in many devel- oping countries, the figure reaches six per cent because of the greater frequency of disorders related to maternal age (such as mental retar- dation due to Down's Syndrome), and of inherited disorders of the red blood cell (sickle cell disease, the thalassaemias and G6PD deficiency). Infants with genetic diseases are particularly vulnerable to infectious and nutritional diseases. So when the infant mortality is high, most die undiagnosed in early childhood, creating the impression that heredi- tary disorders are not a significant health problem. For instance, in Sub-Saharan Africa, between one and two per cent of all infants are born with sickle cell disease, and the vast majority die in their first two years from anaemia or infec- tions. In addition, about 20 per cent · of male infants have glucose-6- phosphate dehydrogenase (G6PD) deficiency, and probably one-tenth of them die or are disabled as a re- sult of severe neonatal jaundice. The result is that these two inherit- ed diseases kill between two and three per cent of African infants, and contribute up to 20 per cent of the infant mortality, without attracting particular attention. Infant mortality is falling wher- 20 ever WHO programmes of immuni- zation, diarrhoea management and malaria control are making pro- gress . As a direct result, more in- fants with hereditary disabilities are surviving and being diagnosed, and will then require ma~agement, as far as it is available. The propor- tion of infants born with hereditary A parent with A parent with thassalaemiatrait Normal Thalassaemia trait Thalassaemia major If both parents carry thalassaemia trait, their children may have thalas- saemia trait, or they may have com- pletely normal blood, or they may have thalassaemia major. In each pregnancy there is a one in four (25 %) chance that their child will have normal blood, a two in four (50 %) chance that the child will have thalassaemia trait, and a one in four (25 %) chance that the child will have thalassaemia major. Photo WHO disease who survive to older age- groups can be regarded as a built-in " thermometer" to measure the progress of primary health care measures. Though the numbers of children affected are relatively small com- pared with infectious or nutritional conditions, hereditary diseases cause life-long problems, and pre- sent a disproportionate burden for the patients, their families, and the health care system, whatever its stage of development may be. An inherited disease can even emerge rather suddenly in a progressive country as a priority health prob- lem. This happened with thalassae- mia in Cyprus, Greece and Italy in the 1960s and the same is now hap- pening in Bahrain, the Republic of Maldives and Thailand. These facts require new perceptions on the part of health planners. It is too easy to suppose that, be- cause hereditary diseases are in- born, very little can be done about them, but this is not the case. Neo- natal jaundice due to G6PD defi- ciency can be prevented by educat- ing mothers and health workers to avoid factors that can precipitate it (such as herbal medicines or keep- ing infant clothes in mothballs) and, providing health workers are trained to recognise it, it can usual- ly be successfully treated simply by exposing the infants to sunlight. Children with sickle cell disease can be protected by teaching the par- ents to avoid extremes of tempera- ture and dehydration, and to seek rapid treatment for infections. Of course, many hereditary dis- eases are more intractable. Some treatments are complex and expen- sive; thalassaemia major for in- stance requires monthly blood transfusions and a daily infusion of an iron-chelating drug (one which promotes a suspension of iron sub- stances in the blood). Others, like mental retardation due to Down's Syndrome, cannot be treated at all. But in some cases even these prob- lems can be overcome. For exam- WoRLD HEALTH, October 1988 ple, thalassaemia and sickle cell dis- ease can be prevented through edu- cation and carrier testing and infor- mation, when prenatal diagnosis is available. Such diseases as thalassaemia, sickle cell disease, cystic fibrosis and phenylketonuria are transmit- ted by symptomless carriers, who inherited the "trait" from their parents. In Africa and Asia, from between one and 25 per cent of most populations are carriers of one of these disorders which, rather surprisingly, serves as a constitu- tional protection against malaria. If a carrier and non-carrier marry, some of their children are carriers and some are not, but none have the major disease. However, if two carriers marry, on average one in four of their children will inherit the disorder from both parents, and will have sickle cell disease or thalassaemia major. Very simple blood tests are suffi- cient to identify carriers, so couples who are carriers can be detected and advised of their risk before they start a family. We now know that most people wish to know these facts . Information on genetic risk and ways of avoiding it must be given according to the basic ethi- cal principles of medical genetics. These are : that the autonomy of the individual or the couple must be respected; that they have the right to full information given in a way they can understand; and that confidentiality must be preserved. When carriers are detected and informed according to these princi- ples, they do not usually let the in- formation influence their choice of marriage partner, but it does influ- ence their reproductive behaviour. So the important message to give to such couples is that to be a carrier is harmless to themselves, that they have a high chance of having healthy children, and that the birth of sick children can be avoided through prenatal diagnosis with se- lective abortion of affected fetuses. The techniques for prenatal diagno- sis are steadily becoming more sim- ple-for instance, it can now be done around nine weeks into the pregnancy by chorionic villus sam- pling (CVS), allowing early termi- nation of pregnancy when this is re- quested. Gene-mapping methods for prenatal diagnosis are also be- W oRLD HEALTH, October 1988 As health care improves, more infants with hereditary disabilities are surviv - ing to older age. They represent a " thermometer" to measure the pro- gress of primary health care measures. Photo WHO/Zafar Italy and Cyprus, and as a result the birth rate of affected infants has fallen by about 70 per cent in Greece and 50 per cent in Italy, and is still falling fast in both countries. In Cyprus, progress has been even more rapid: in 1986 no new affect- ed infants were born, as a result of coming simpler, and will soon be the informed choice of couples at suitable for use in developing risk. Simultaneously, an improved countries. service has been built up for the The strategy for community con- affected patients. This approach is trol of hereditary diseases corn- now beginning to find support in bines treatment and prevention in a parts of Asia. unified approach. The objectives The strategy of hereditary dis- are to develop community educa- ease control is in the mainstream of tion and involvement, appropriate WHO's approach to health promo- management, and prevention tion, since it depends on communi- through population screening and ty education and participation, and counselling, preferably with access on the development of appropriate to prenatal diagnosis. The primary technology. Genetic technology is aim of the prevention component is developing very rapidly; in the to provide information and offer near future it will become possible parents a choice, but it is already to detect carriers for other inherit- clear that making these facilities · ed diseases such as cystic fibrosis. available often leads to a major re- · The programmes for the haemoglo- duction in new births of affected binopathies provide a model on infants. how to apply this knowledge- by In the Mediterranean area, for putting information into the hands example, large-scale WHO thalassae- of people themselves, so that they mia control programmes have start- can protect the health of their ed over the last decade in Greece, families. • 21