Review of neonatal screening programme for phenylketonuria

Food Regime for Phenylketonuria: Presenting Complications and Possible Solutions

In the category of rare inherited genetic disorders, phenylketonuria is a prominent example. Here, the defective phenylalanine hydroxylase enzyme fails to catalyze conversion of phenylalanine to tyrosine. This leads to not only excess deposition of phenylalanine leading to phenylalanine toxicity but also precludes the production of important glutamatergic and cholinergic neurotransmitters, leading to epileptic disorders, microcephaly, low intelligence quotient etc. For long, specialized food products are considered as preferred solution to prevent disease outcome. Different medical diets are developed for managing phenylketonuria includes amino acid mixtures, protein hydrolysates, cofactor-based therapy, large neutral amino acids and glycomacropeptides. However, despite the advent of alternate forms of diet products, the central form of treatment has still been free amino acid mixture. The formulated diet is by and large expensive and in-depth evaluation of several factors which contribute to the expense of medicated diet is requisite to create effective yet affordable avenues for management of disease. For this, we have discussed the role of various factors involved in increasing price of medicated diet and presented possible solutions to it. We have also extensively reviewed prevalence of disease, commercial diet for PKU patients, and their associated limitations. Overall, this is the first attempt to present a holistic view of balance between the overall impact of diet associated therapy and weighing it against the associated finances incurred.

An enzyme cascade fluorescence-based assay for the quantification of phenylalanine in serum

An enzyme cascade fluorescence assay for phenylalanine quantification was established by the combination of phenylalanine dehydrogenase and nitroreductase.

Global prevalence of classic phenylketonuria based on Neonatal Screening Program Data: systematic review and meta-analysis

Phenylketonuria is a disease caused by congenital defects in phenylalanine metabolism that leads to irreversible nerve cell damage. However, its detection in the early days of life can reduce its severity. Thus, many countries have started disease screening programs for neonates. The present study aimed to determine the worldwide prevalence of classic phenylketonuria using the data of neonatal screening studies. The PubMed, Web of Sciences, Sciences Direct, ProQuest, and Scopus databases were searched for related articles. Article quality was evaluated using the Joanna Briggs Institute Critical Appraisal Evaluation Checklist. A random effect was used to calculate the pooled prevalence, and a phenylketonuria prevalence per 100,000 neonates was reported. A total of 53 studies with 119,152,905 participants conducted in 1964-2017 were included in this systematic review. The highest prevalence (38.13) was reported in Turkey, while the lowest (0.3) in Thailand. A total of 46 studies were entered into the meta-analysis for pooled prevalence estimation. The overall worldwide prevalence of the disease is 6.002 per 100,000 neonates (95% confidence interval, 5.07-6.93). The metaregression test showed high heterogeneity in the worldwide disease prevalence (I2=99%). Heterogeneity in the worldwide prevalence of phenylketonuria is high, possibly due to differences in factors affecting the disease, such as consanguineous marriages and genetic reserves in different countries, study performance, diagnostic tests, cutoff points, and sample size.

Successful Live Birth following Preimplantation Genetic Diagnosis for Phenylketonuria in Day 3 Embryos by Specific Mutation Analysis and Elective Single Embryo Transfer

Phenylketonuria (PKU) is an autosomal recessive inherited metabolic disorder caused by a complete or near-complete deficiency of the liver enzyme phenylalanine hydroxylase (PAH), which converts the amino acid phenylalanine to tyrosine, leading to the increase of blood and tissue concentration of phenylalanine to toxic levels. PKU is not life threatening but is treated through lifelong dietary management. If untreated, it can lead to severe learning disability, brain function abnormalities, behavioural and neurological problems. The non-life threatening nature of PKU has until now caused some debate on whether to licence its detection by preimplantation genetic diagnosis (PGD). We report the first successful live birth in the UK following single cell embryo biopsy and PGD for the detection of two different mutations in the (PAH) gene. This case highlights both an important scientific development as well as the ethical challenge in offering couples who carry PKU this new reproductive option when starting their family.

Molecular genetics and impact of residual in vitro phenylalanine hydroxylase activity on tetrahydrobiopterin responsiveness in Turkish PKU population

BACKGROUND

The prevalence of phenylalanine hydroxylase (PAH)-deficient phenylketonuria (PKU) in Turkey is high (1 in 6500 births), but data concerning the genotype distribution and impact of the genotype on tetrahydrobiopterin (BH(4)) therapy are scarce.

OBJECTIVE

To characterize the phenotypic and genotypic variability in the Turkish PKU population and to correlate it with physiological response to BH(4) challenge.

METHODS

We genotyped 588 hyperphenylalaninemic patients and performed a BH(4) loading test (20mg/kg bw) in 462 patients. Residual PAH activity of mutant proteins was calculated from available in vitro expression data. Data were tabulated in the BIOPKU database (www.biopku.org).

RESULTS

Eighty-eight mutations were observed, the most common missense mutations being the splice variant c.1066-11G>A (24.6%). Twenty novel mutations were detected (11 missense, 4 splice-site, and 5 deletion/insertions). Two mutations were observed in 540/588 patients (91.8%) but in 9 patients atypical genotypes with >2 mutations were found (8 with p.R155H in cis with another variant) and in 19 patients mutations were found in BH(4)-metabolizing genes. The most common genotype was c.1066-11G>A/c.1066-11G>A (15.5%). Approximately 22% of patients responded to BH(4) challenge. A substantial in vitro residual activity (average >25% of the wild-type enzyme) was associated with response to BH(4). In homozygous genotypes (n=206), both severity of the phenotype (r=0.83) and residual PAH activity (r=0.85) correlate with BH(4) responsiveness.

CONCLUSION

Together with the BH(4) challenge, these data enable the genotype-based classification of BH(4) responsiveness and document importance of residual PAH activity. This first report of a large-scale genotype assessment in a population of Turkish PKU patients also documents a high prevalence (47%) of the severe classic phenotype.

Determination of phenylalanine and tyrosine in plasma and dried blood samples using HPLC with fluorescence detection

The determination of phenylalanine and tyrosine is presently the most reliable direct approach to the diagnosis of phenylketonuria. An HPLC method for the simultaneous measurement of phenylalanine and tyrosine in samples of dried blood spots and plasma has been developed and evaluated. We have used an inherent fluorescence of both phenylalanine and tyrosine. For the separation, a reverse-phase column LiChroCart 125-4, Purospher RP-18e, 5microm, was used. The mixture of ethanol and deionized water (5:95, v/v) was used as a mobile phase. Analytical performance of this method is satisfactory for both phenylalanine and tyrosine: the intra-assay and inter-assay coefficients of variation were below 10%. Quantitative recoveries from spiked plasma and blood samples were between 92.0 and 102.9%. The limit of detection was 10.0 and 5.0micromol/L, respectively. The preliminary reference ranges of phenylalanine and tyrosine in a group of newborns are 69.3+/-13.1 and 42.7+/-12.9micromol/L, in a group of blood donors are 68.4+/-9.9 and 52.1+/-10.9micromol/L. The presented method is inexpensive and suitable for diagnosis of phenylketonuria.

Newborn bloodspot screening in the UK – past, present and future

Screening newborn babies for inherited metabolic disease began in the UK in the late 1950s with the ‘nappy test’ for phenylketonuria. In 1969 the Department of Health recommended changing to bloodspot screening using the techniques developed in the USA by Robert Guthrie and his associates. Bloodspot screening for various other disorders (galactosaemia, maple syrup urine disease, homocystinuria, cystic fibrosis and others) was introduced on a patchy local basis but, until 2000, the only additional disorder officially recommended was congenital hypothyroidism. Screening for haemoglobinopathies received official support in 2000 and for cystic fibrosis in 2001 though implementation was slow, particularly for the latter. Both these screens have raised difficult issues relating to genetic privacy and the detection of carrier status in children. During the last decade screening has become increasingly subject to central control. Though a more consistent and systematic approach was clearly needed, this has undoubtedly slowed the rate of innovation. In particular the UK has lagged behind many other European countries in the application of tandem mass spectrometry (MS-MS) though, following a major pilot study, screening for medium-chain acyl-CoA dehydrogenase deficiency is now in the process of introduction. Attempts to codify clinical and laboratory procedures have also proved controversial, highlighting marked differences in practice in various parts of the country and the difficulty of rationalizing these within a practicable and scientifically justified framework. Notwithstanding this, there are many positive developments and newborn screening remains a stimulating and rewarding field in which to work.

Peak bone mass in patients with phenylketonuria

OBJECTIVE

Several studies have suggested a compromised bone mass in phenylketonuria patients but most reported on heterogeneous or small patient groups. Our aim was to evaluate peak bone mass in adult PKU patients and to relate BMD to nutritional parameters.

PATIENTS AND METHODS

BMD was measured by dual-energy x-ray absorptiometry in 31 adult PKU patients (18 female), mean age 25 +/- 5.3 years. Nutritional intake was calculated based on food diaries. Diet adherence was determined based on patients' report.

RESULTS

Mean blood phenylalanine (Phe) concentration was 968 +/- 526 micromol/L (16 +/- 8.7 mg/dl). Eight patients (32.2%) met the recommended blood Phe concentration of <726 micromol/L (<12 mg/dl), and there was no significant difference in Phe concentrations between diet-adherent and non-adherent patients. Osteopenia was detected in 11 patients (38.7%), while osteoporosis was detected in 2 patients (6.5%). No correlation was found between BMD and age, blood minerals, Phe, vitamin D and alkaline phosphatase levels, calcium and protein intake, body mass index, and body fat percentage.

CONCLUSIONS

Peak bone mass is decreased in PKU patients. Possible explanations include long-standing dietary deficiency in protein, calcium, vitamin D or trace elements, or a primary defect in bone turnover inherent to the disease itself. Our data do not favour any of these hypotheses. Further studies are needed to elucidate the cause of low bone density in PKU patients.

Informed choice and public health screening for children: the case of blood spot screening

OBJECTIVE

To examine parents' and health professionals' views on informed choice in newborn blood spot screening, and assess information and communication needs.

DESIGN AND PARTICIPANTS

A qualitative study involving semi-structured telephone interviews and focus groups with 47 parents of children who were either found to be affected or unaffected by the screened conditions, and 35 health professionals with differing roles in newborn blood spot screening programmes across the UK.

RESULTS AND CONCLUSIONS

Parents and health professionals recognize a tension between informed choice in newborn blood spot screening and public health screening for children. Some propose resolving this tension with more information and better communication, and some with rigorous dissent procedures. This paper argues that neither extensive parent information, nor a signed dissent model adequately address this tension. Instead, clear, brief and accurate parent information and effective communication between health professionals and parents, which take into account parents' information needs, are required, if informed choice and public health screening for children are to coexist successfully.

Timeline: Raising the profile of genetics in primary care

Primary care practitioners recognize that genetics is relevant to their daily practice, for example, for detecting and managing the risk of multifactorial disorders and genetic reproductive risks, and, in future, for targeted drug therapy. However, they lack confidence in their ability to apply genetic approaches. In fact, genetics is already ingrained in current practice, and the development of appropriate guidelines and web-based information resources will help practitioners to make personalized genetic risk assessment a part of holistic, patient-oriented primary health care.

Expanded newborn screening in Bavaria: tracking to achieve requested repeat testing

OBJECTIVES

Expansion of newborn screening programs may increase the risk of missing cases through procedural failures. A coordinated process quality assurance procedure to track recalls was, therefore, introduced in parallel to expansion (including MS-MS and 17alpha-OHP) in Bavaria.

METHODS

Using comprehensive computerized registration and automated monitoring a state-funded center coordinated all individual measures to achieve complete testing of all repeat requests-case-specific contacts to physicians, midwives, and parents. Mailing and phoning from the center were supplemented by local public health activities including home visits if needed.

RESULTS

Among 243,422 children tested in 1999 and 2000 overall recall was 3.62% (8,809 children): 0.30% (726) were due to sample inadequacy, 1.35% (3,282) to early sampling (<48 h), and 1.97% (4,801) to abnormal results. Of all recalls, 80.9% were received following the initial request, 1,679 (19.1%) required special efforts. Of these, 873 were achieved following a single and 601 following repeated central activities, and 102 were achieved following local support. Sixty-three cases of parental refusal and 47 untraceable children remained. Altogether, 98.8% recalls were achieved, corresponding to 99.96% of all tested children for which definite screening results could be obtained.

CONCLUSIONS

Expansion of newborn screening programs does not necessarily mean unsolvable problems in tracking of recalls if adequate logistics is established in parallel.

Genetic services

This is a time of unprecedented increase in knowledge about the genetic basis of disease against a background of rapidly changing technology. Advances happen quickly, with the new knowledge rapidly becoming relevant to services for patients, and hence there is an increasing demand for, and expectation of, genetic services. This brings a challenge for health services worldwide to keep pace with the expectations of their populations. There is also a need for public and professional education and dialogue to dispel some of the hype and myths about what can be achieved. It should not be forgotten that any services must be provided and developed within a broad ethical framework. A statement from a WHO expert consultation (1) concluded that 'Genetic advances will only be acceptable if their application is carried out ethically, with due regard to autonomy, justice, education and the beliefs and resources of each nation and community'. That so many public bodies have commented on genetic services and their associated ethical, legal and social issues emphasizes not only the importance of this area in health care, but also that the wider issues are of great importance in democratic societies. The aim of this paper is to review the current situation in the provision of genetic services, to examine the drivers for change, to speculate on the likely need for future services and to suggest models for the development of such services. Pharmacogenetics and the determination of genetic factors indicating susceptibility to infection will not be discussed since these have been the subject of several recent excellent reviews (2, 3). Genetic services have been defined as health measures implemented to help people with a genetic disadvantage and their families to live and reproduce as normally as possible (4). Broadly they can be divided into those services which target whole populations with a view to identifying those at increased risk; and those which focus on the needs of families which are affected by a genetic disorder or who perceive themselves to be at increased risk.

Neonatal screening and long-term follow-up of phenylketonuria: the French database

BACKGROUND

In France, neonatal screening of phenylketonuria (PKU) started in 1966. A national association was created in 1978 in order to organise the neonatal screening program and to control the efficacy of the screening and patients' follow-up.

AIMS

To evaluate the results of the French PKU screening program in terms of hyperphenylalaninaemia epidemiology, efficacy of the screening procedure, management and outcome of the patients.

STUDY DESIGN

The national database has been filled-up first with the answers to questionnaires that were sent each year by the PKU patients' physicians, and second with the results of an additional inquiry, which was set up in 1994 in order to investigate diagnosis, treatment, and school outcome of all French PKU patients.

RESULTS

PKU was diagnosed in 81.6% of patients with hyperphenylalaninaemia (HPA), non-PKU HPA in 17.2% and cofactor deficiency in 1.1%. From 1980, incidence of PKU has been stable: 1 per 17,124 live births. Sensitivity of the screening procedure was 99.3%. Age at diet initiation regularly decreased to reach 14 days as a median in 1996. Until 1990, median age at diet discontinuation was 6 years of age. Later, strict diet was continued longer (at least, up to 8-10 years). PKU patients who entered to secondary school at normal age were characterised by an earlier age at diagnosis and at diet initiation and a later age at diet discontinuation, compared to those who entered 1 year or more behind normal age.

CONCLUSION

These data confirm the benefit of a nationwide organised screening program. They emphasise the importance of an early neonatal diagnosis and diet initiation in PKU patients and are consistent with the benefit of a longer period of strict diet in childhood.

Overview of common inherited metabolic diseases in a Southern Chinese population of Hong Kong

BACKGROUND

The Joint metabolic clinic at the Prince of Wales Hospital was established in January 1997 to provide a comprehensive multi-disciplinary care to patients with inherited metabolic diseases (IMDs). Patients are referred from both within and outside our hospital. Until July, 2000, more than 40 patients and families with 20 different biochemical diagnoses attend the clinic for regular follow up. A pattern of more common IMDs among Hong Kong Chinese emerged from our case registry. In order to advance the understanding of Chinese metabolic diseases, we examined the molecular basis of those diseases with unique features in Chinese or were locally prevalent. Mutations were found in patients with primary carnitine deficiency, ornithine transcarbamylase deficiency, X-linked adrenoleukodystrophy, glutaric aciduria type I, and galactosemia. We also analyzed the mutations in multiple carboxylase deficiency and Niemann-pick type C on four families.

CONCLUSIONS

Although IMDs are a significant cause of mortality and morbidity among pediatric patients, with a better understanding of the molecular genetics of these diseases, prenatal diagnosis of these common IMDs will be facilitated, which is currently the most effective way of controlling IMDs.

Coverage of neonatal screening: failure of coverage or failure of information system

OBJECTIVES

To evaluate neonatal screening coverage using data routinely collected on the laboratory computer.

SUBJECTS

90 850 births in 14 North East Thames community provider districts over a 21 month period.

METHODS

Births notified to local child health computers are electronically copied to the neonatal laboratory computer system, and incoming Guthrie cards are matched against these birth records before testing. The computer records for the study period were processed to estimate the coverage of the screening programme.

RESULTS

Out of an estimated 90 850 births notified to child health computers, all but 746 (0.82%) appeared to have been screened or could be otherwise accounted for (0.14% in non-metropolitan districts, 0.39% in suburban districts, and 1.68% in inner city districts). A further 893 resident infants had been tested, but could not be matched to the list of notified resident births. The calculated programme coverage already exceeds the 99.5% National Audit Programme standard in 7/14 districts. Elsewhere it is not clear whether it is coverage or recording of coverage that is low.

CONCLUSION

Previous reports of low coverage may have been exaggerated. High coverage can be shown using routine information systems. Design of information systems that deliver accurate measures of coverage would be more useful than comparison of inadequately measured coverage with a national standard. The new NHS number project will create an opportunity to achieve this.

Increased risk of vitamin B12 deficiency in patients with phenylketonuria on an unrestricted or relaxed diet

OBJECTIVE

To investigate whether dietary relaxation or cessation in patients with phenylketonuria (PKU) predisposes to vitamin B12 deficiency.

STUDY DESIGN

Patients with PKU aged 11 to 38 years underwent a neurologic examination and dietetic assessment and were divided according to their diet into 1 of 3 groups: Strict - those on a strict low phenylalanine (phe) diet with amino acid, mineral, and vitamin supplements; Relaxed - those on a total protein intake of approximately 1 g/kg/d with 50% of this from natural protein and 50% from amino acid, mineral, and vitamin supplements; Unrestricted - those on no formal protein restriction and not taking amino acid supplements. Assays of blood samples were taken for vitamin B12 and folate levels by standard assays. Results were analyzed with Student t test.

RESULTS

Vitamin B12 levels were significantly lower in the PKU groups on relaxed or unrestricted diets compared with the normal population (P <.0001 [unrestricted] and.0034 [relaxed]). Folate levels were significantly elevated in all PKU groups (<.0001).

CONCLUSION

Patients with PKU who are no longer under strict dietary control may be at risk from vitamin B12 deficiency. We recommend that all patients should remain under medical and dietetic supervision and in particular have their vitamin B12 status monitored.

The use of the dried blood spot sample in epidemiological studies

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Secondary analysis of economic data: a review of cost-benefit studies of neonatal screening for phenylketonuria

STUDY OBJECTIVE

To estimate the net financial benefit of neonatal screening for phenylketonuria (PKU): by a simple pooling of cost data from the literature; and by a more complex modelling approach.

DESIGN

A systematic literature review was conducted to identify papers containing data on the monetary costs and benefits of neonatal screening for PKU. The methodological quality of the studies was appraised, and data were extracted on resource use and expenditure. Monetary data were converted to common currency units, and standardised to UK incidence rates. Net benefits were calculated for median, best case and worst case scenarios, and the effect of excluding poor quality studies and data was tested. The net benefit was also estimated from a model based on data from the literature and assumptions appropriate for the current UK situation. Extensive sensitivity analysis was conducted.

MAIN RESULTS

The direct net benefit of screening based on the median costs and benefits from the 13 studies identified was 143,400 Pounds per case detected and treated (39,000 Pounds and 241,800 Pounds for worst case and best case scenarios respectively). The direct net benefit obtained by the modelling approach was lower at 93,400 Pounds per case detected and treated. Screening remained cost saving under sensitivity analysis, except with low residential care costs (less than 12,300 Pounds per annum), or very low incidence rates (less than 1 in 27,000).

CONCLUSIONS

The economic literature on PKU screening is of variable quality. The two methods of secondary analysis lead to the same conclusion: that neonatal PKU screening is worthwhile in financial terms alone in the UK, and that it justifies the infrastructure for collecting and testing neonatal blood samples. This result cannot necessarily be extrapolated to other countries.

Audit of neonatal screening programme for phenylketonuria and congenital hypothyroidism

The performance of the neonatal screening programme was audited against clinical standards in the Bath clinical area from 1 April 1994 to 31 March 1996. The standards and policy were agreed by local service provider representatives of the screening and were audited, using laboratory and child health computer systems and medical records. Two annual reports were produced with recommendations for improvement communicated to representatives of the service. Thus the first audit loop has been completed. The audit shows that the coverage of the service is excellent, with all eligible babies being offered screening; those with congenital hypothyroidism or phenylketonuria receive appropriate treatment by the 28 day standard. The process works extremely well, although areas for improvement have been identified, to increase the efficiency of the service. It is concluded that an effective and efficient audit cycle can be established, to monitor and improve the performance of the neonatal screening service.

Newborn phenylketonuria (PKU) Guthrie (BIA) screening and early hospital discharge

Recent policies of early discharge of postpartum mothers and their infants has raised concerns of possible decreased sensitivity in Guthrie bacterial inhibition assay (BIA) phenylketonuria (PKU) screening resulting in missed cases. In order to assess the potential impact of early discharge from hospital on neonatal screening for PKU and its variants, we performed 18 standard BIA screening tests on 11 newborn infants with the disease. Blood spot samples were collected from 1 to 24 h after birth and were analyzed at the Ontario Ministry of Health newborn screening laboratory according to the routine screening protocol. Except for one 4-hour postnatal sample from an infant with 'non-PKU mild hyperphenylalaninemia' (MHP) all blood samples showed phenylalanine levels > or = 240 mumol/l, irrespective of the age of the baby. During our 29 year experience with neonatal PKU screening (3.9 million infants tested), employing a cutoff blood phenylalanine of 240 mumol/l in blood spots obtained at > or = 24 h of age, only two biological false negative (one confirmed) tests were discovered in infants subsequently shown to have classical PKU: another three false negative tests were discovered in sibs of infants with MHP. The sensitivity of the screening test was 99.2% for infants with classical and mild PKU. Ascertainment of patients with MHP is unknown and is very likely incomplete. Over a 3-year period (1992-4) the specificity of the test was 99.9% for those screened after 24 h. The positive predictive value was 12.8%. Although early discharge may have an impact on other screened diseases, we conclude, from our studies, that early discharge may not affect the detection of infants with classical and mild (atypical) PKU, but would probably increase the number of infants with MHP missed using the BIA and a cutoff level of 240 mumol/l. Because of our experience and that of others, we recommend that neonates be at least 12 h of age before initial BIA PKU screening be carried out. To confirm this recommendation further prospective studies should be initiated.

Impact of incomplete coverage of neonatal dried blood spot screening on estimating HIV-1 seroprevalence

The aim of this study was to determine the extent to which selective under-coverage of births to mothers more likely to be at risk of HIV-1 infection will result in a significant under-estimation of the true neonatal seroprevalence. Census data, local birth statistics, maternity data and data from the prevalence monitoring programme were used to produce a model to predict the effects of under-coverage in the uptake of neonatal metabolic screening which has been observed in babies with a mother of ethnic group black African. The adjustment factor which allows for under-coverage is the relative inclusion ratio (RIR); the probability that samples from a group at different risk of HIV infection were included in the survey divided by the probability of inclusion for samples from all other babies. The RIR was found to be close to unity (0.97), indicating a minimal bias. Under usual conditions only if the relative inclusion ratio (RIR) declined to values of 0.87 or below would there be a substantial bias. Despite some selective under representation, the results obtained from the Unlinked Anonymous HIV Monitoring Programme Dried Blood Spot Survey would seem to identify levels of prevalence in the population of child-bearing women with a good degree of accuracy and remains a useful tool for resource allocation, planning of services, provision of care and counselling.

An audit of the organisation of neonatal screening for phenylketonuria and congenital hypothyroidism in the Northern Region

BACKGROUND

The objectives of the study were to identify whether all districts in the Northern Region had a system in place to ensure that all resident babies were being screened for phenylketonuria and congenital hypothyroidism and to identify potential delays which could influence whether a result was available on all residents before 28 days of age.

METHODS

Lead professionals involved in the screening programmes were interviewed in 1993 in all 16 districts. Recommendations for improving the service were made to each district. Six months later a follow up telephone interview with the doctor involved in the screening programmes was undertaken to identify the changes that had been made in the service.

RESULTS

In 1993 three districts made no attempt to match neonatal screening results to birth notifications. Of the 13 districts that undertook matching, two districts did no further checks to identify babies without a result and five districts undertook a check on a monthly basis only. Only six districts were, therefore, found to have a timely fail-safe system for checking that results were available for resident babies. In 1994, following recommendations to improve the timeliness and completeness of the screening programmes, all districts except two had improved their fail-safe systems.

CONCLUSION

This multi-disciplinary regional audit resulted in organisational improvements to the neonatal metabolic screening programmes in the Northern Region.

Variation in coverage by ethnic group of neonatal (Guthrie) screening programme in south London

OBJECTIVES

To determine whether coverage of the neonatal (Guthrie) screening programme in Britain is different for groups at highest risk of sickle cell disease and to identify possible reasons for incomplete coverage.

DESIGN

Descriptive study of coverage of screening programme and its variation by mobility, district of residence, and ethnic group.

SUBJECTS

1727 infants born between 1 October and 31 December 1991.

SETTING

Former West Lambeth and Camberwell District Health Authorities, London.

MAIN OUTCOME MEASURE

Proportion of infants with an identifiable screening test result.

RESULTS

Screening covered 1663/1727 (96.3%) infants overall (745/786 (94.8%) in West Lambeth; 918/941 (97.6%) in Camberwell). The relative odds ratio of an African infant not having been tested compared with a white infant was 3.05 (95% confidence interval 1.30 to 7.14) (2.08 (0.86 to 5.01) after adjustment for mobility and district of residence). For infants whose families moved into the districts after the birth compared with those born and resident in the districts the relative odds ratio of having been tested was 10.16 (4.85 to 21.29). The odds ratio of locally delivered infants in West Lambeth not having been tested compared with those in Camberwell was 2.12 (1.08 to 4.16) after adjustment for ethnic group.

CONCLUSION

Coverage of the screening programme is incomplete and poorer in infants of African ethnic group than in white infants. Poorer coverage is also associated with mobility of the family around the time of birth. The findings have implications for using the neonatal programme for testing for sickle cell disease and other disorders. Arrangements for monitoring the existing screening programme are inadequate and an improved system should be established, similar to the scheme that monitors the immunisation programme.

Intelligence in mild atypical phenylketonuria

In 82 children with mild phenylketonuria (PKU) (blood phenylalanine (Phe) concentrations consistently below 900 mumol/l throughout follow up) the relationship between intelligence at age 4 (IQ by Stanford-Binet) and average blood Phe concentrations from birth to 4 years was examined. Of the 82 children 24 had received no treatment. In the group as a whole, and in the 24 untreated subjects alone, mean IQs were significantly below population norms, with deficits of approximately 4.5 points and 9 points respectively. After allowing for social class IQ fell progressively by approximately 6 points for each 100 mumol/l rise in mean Phe concentrations in both the treated and untreated subjects. This relationship resembled that previously reported in early treated children with more severe forms of PKU, except that the scale of the relationship was even greater. We conclude that all children whose blood Phe concentrations reach 400 mumol/l or above should receive a low Phe diet, at least during the preschool years, and that the aim should be to control blood Phe levels below 400 mumol/l throughout early childhood in all forms of PKU.

Development of an enzyme-mediated assay for phenylalanine in blood spots

We describe the optimization of a rapid procedure for the elution of phenylalanine from blood spots and the estimation of the amino acid eluted using an enzyme-mediated assay linked to a colorimetric detection system. The method is rapid, fully quantitative, interference-free, accurate and precise unlike many of the methods currently employed for phenylalanine determination. The performance of the proposed method may necessitate the review of reference ranges and cut-off assignment strategies.

Phenylketonuria due to phenylalanine hydroxylase deficiency: an unfolding story. Medical Research Council Working Party on Phenylketonuria

Efficient neonatal screening for phenylketonuria and the availability of complex diets for lifelong use have virtually eliminated severe mental handicap from the disease. Nevertheless, there remains a high risk of fetal damage in offspring of women with the disease, and the possibility that the diets themselves may be harmful cannot be excluded. Search for a preventive treatment for the disease has been greatly aided by advances in molecular genetics. For example, in mice modified liver cells have been implanted, which have not only corrected the phenylalanine defect but have remained healthy for the normal life span of the animal. Overall, however, prevention and treatment have not progressed as quickly as was hoped, and research and development must be pursued vigorously to take account of contemporary perceptions of the disorder.

Plasma phenylalanine and tyrosine levels revisited in heterozygotes for hyperphenylalaninaemia

We examined the value of the fasting plasma phenylalanine/tyrosine ratio obtained in an ordinary clinical setting for assessing the probability of being a heterozygote for hyperphenylalaninaemia. This biochemical test was found to be of little value in those with a high (66%) prior risk of heterozygosity, because it could not reduce the risk below 12%. However, in a population with a prior risk of only 2%, it discriminates the 3% with a 19% risk from the 97% with a risk of 1.5% or less. This simple method could usefully be applied to such a population, in order to select those at higher risk for further investigation using molecular genetics.

Development and validation of a robust specific enzyme mediated assay for phenylalanine in serum

The specificity of a phenylalanine dehydrogenase, particularly with respect to cross reactivity toward tyrosine, has been shown to be pH dependent, being minimal at high pH. The dehydrogenase step has been coupled to colorimetric detection of NADH using a tetrazolium salt. The assay shows no significant cross reactivity towards a range of amino acids or drugs and correlates well with an established HPLC technique.