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Newborn screening to detect "hidden" diseases


In most of the developed countries rigorous steps are taken to diagnose many hidden problems of the baby either prior to birth or immediately after birth. One such manoeuvre is screening of a sample of blood from the newborn baby for a number of diseases and deficiencies. In many lands of the Western world and especially in the United States of America, it is mandatory to perform these tests on all newborn babies. Even some of the more affluent countries in the Asian region have now joined the club of countries involved in countrywide newborn screening programmes. Some of these affected babies may appear quite normal at birth but harbour "hidden" defects and deficiencies that could lead to major problems as the babies grow up. The newborn screening programmes are designed to detect them as soon as feasible.

Newborn screening is the process of testing newborn babies for treatable genetic, endocrine, metabolic and haematological diseases. Doctor Robert Guthrie is given much of the credit for pioneering the earliest screening for phenylketonuria in the late 1960s using blood samples on filter paper. The blood is obtained by pricking a newborn baby’s heel on the second day of life to get a few drops of blood. Congenital hypothyroidism was the second disease widely added in the 1970s. The development of tandem mass spectrometry screening by Edwin Naylor and others in the early 1990s led to a large expansion of potentially detectable congenital metabolic diseases that affect blood levels of organic acids. Additional tests have been added to many screening programs over the last two decades. Newborn screening has been adopted by most countries around the world, though the lists of screened diseases vary widely. The problem with many of these hidden diseases is that if left untreated from very early on in life, these could lead to permanent and irreversible harm to the baby, particularly brain damage. Blood is taken from the baby around 24 to 48 hours after birth. The great advantage of the filter paper method is that the blood impregnated filter paper could even be sent by post to a regional or reference laboratory. In mass screening situations, the results are generally available within 2 to 3 weeks.

There are some important considerations that go into the decision making process as to whether a particular type of screening programme should be adopted. It is generally utilised for a disease that can be missed by clinical examination at birth. The disease should have a high enough frequency in the target population and a delay in diagnosis should be known to induce irreversible damage to the baby. A simple and reasonably reliable diagnostic test for the disease should be available and treatment or intervention should be known to make a difference if the disease is detected early.

Some of the more important diseases for which screening is available are given below :-

* Congenital hypothyroidism (CH). This is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn infants has a severe deficiency of thyroid function while even more have deficiencies of mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism can lead to growth failure and permanent mental retardation. Treatment consists of a daily dose of thyroid hormone (thyroxine) by mouth. Because the treatment is simple, effective and inexpensive, nearly all of the developed world practices newborn screening to detect and treat congenital hypothyroidism in the first weeks of life.

* Phenylketonuria (PKU) This is a genetic disorder characterised by a deficiency in the enzyme that is necessary to metabolise the amino acid phenylalanine to the amino acid tyrosine. When the enzyme is deficient, phenylalanine accumulates and is converted into phenylpyruvate also known as phenylketone. If it is left untreated, this condition can cause problems with brain development, leading to progressive mental retardation and seizures. PKU is one of the few genetic diseases that can be controlled by diet. A diet low in phenylalanine and high in tyrosine can be a very effective treatment. There is no cure. Damage done is irreversible so early detection is crucial.

* Congenital adrenal hyperplasia (CAH); This condition leads to a deficiency of the biochemical steps involved in the production of cortisol by the adrenal glands. Most of these conditions involve excessive or deficient production of sex steroids and can alter development of primary or secondary sexual characteristics in some affected infants, children, or adults. Cortisol is an essential hormone and lack of it can lead to fatalities.

* Galactosemia (GAL)) This is a rare genetic metabolic disorder which affects an individual’s ability to properly metabolise the sugar galactose. Lactose in food such as milk is broken down by the body into glucose and galactose. In individuals with galactosemia, the enzymes needed for further metabolism of galactose are severely diminished or missing entirely leading to toxic levels of galactose to build up in the blood. This leads to major problems including brain damage. Without appropriate treatment, mortality in infants with galactosemia is about 75%.

In addition, there are a rather large number of other optional tests that could be done to detect many other conditions. The list grows rapidly virtually every year. In the Asian region, countries such as Singapore and Philippines have well established newborn screening programmes, testing for at least the more common and important diseases. As more and more are added to the list of conditions that could be detected in newborn screening the decision to test for some of these diseases has become a subject of political controversy in the last decade. In mass screening programmes of this nature, careful cost-benefit assessments have to be undertaken before embarking on the venture. The cost should not be a pure expenditure assessment but should also take into account "human factors" such as the disruption of normal life, social disturbances to the family, human suffering and misery etc. It is difficult to resist the appeal of screening when a single child injured by a treatable disease can be shown to the news media and legislature. A prime recent example is the so-called "tale of the two Zacharys". Two California babies, Zachary Wyvill and Zachary Black, were both born with Glutaric acidaemia Type I. The hospital where baby Wyvill was born only tested for the four diseases mandated by state law while baby Black was born in a hospital that was participating in an expanded testing pilot program. Black’s disease was detected at birth and treated with diet and vitamins. Unfortunately, Wyvill’s disease went undetected for over six months and during that time the damage from the enzyme deficiency became irreversible. Lobbyists in many countries pushing for broader and more universal standards for newborn testing are using the tale of the two Zacharys as a tool of powerful persuasion.

As for the situation in our country, paediatricians have been requesting the Ministry of Health to start mass screening programmes for at least a few of the more important defects and diseases. It is essential that all newborn babies are covered by a screening programme. As such, it will need tremendous coordination and will have a considerable cost factor. One of the important diseases which should be considered for screening is congenital hypothyroidism (CH). In the day to day practice, doctors come across children in whom this diagnosis had been missed at birth. By the time they are detected, irreversible brain damage has occurred and even if treatment is started at that stage, the brain defect will persist. This is a preventable disaster as, if the condition was detected at birth and prompt treatment with the hormone thyroxine started, the brain would have developed normally. There lies the crucial importance of newborn screening to detect the problem at birth.

The International Atomic Energy Agency (IAEA) is promoting newborn screening in the Asian region and would help Sri Lanka in this regard. Currently a pilot study on CH is being carried out in the Kandy region and the incidence of congenital hypothyroidism has been estimated to be around 1 in 900 to 1 in 1500. As definitive treatment is available for this condition, this proportion justifies the initiation of a screening programme. Discussions have already commenced among the stakeholders such as the Ministry of Health, The Family Health Bureau, Sri Lanka College of Paediatricians, The Nuclear Medicine facilities and the IAEA regarding the commencement of a newborn screening programmes. Agreement has been reached, at least in principle, of the need for newborn screening. It is envisaged that screening for at least a few of the more common and important diseases could be included in the initial island wide programme.

The writer would appreciate some feed-back from the readers. Please email him at bjcp@sltnet.lk or write to him at the following address: Dr. P. J. C. Perera, Consultant Paediatrician, Asiri Medical Hospital, 181, Kirula Road, Colombo 5.

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