Systematic review and meta-analysis to estimate the birth prevalence of five inherited metabolic diseases

Many newborn screening programmes now use tandem mass spectrometry in order to screen for a variety of diseases. However, countries have embraced this technology with a differing pace of change and for different conditions. This has been facilitated by the ability of this diagnostic method to limit analysis to specific metabolites of interest, enabling targeted screening for particular conditions. MS/MS was introduced in 2009 in England to implement newborn bloodspot screening for medium chain acyl-CoA dehydrogenase deficiency (MCADD) raising the possibility of screening for other inherited metabolic disorders. Recently, a pilot screening programme was conducted in order to evaluate the health and economic consequences of screening for five additional inherited metabolic disorders in England. As part of this study we conducted a systematic review and meta-analysis to estimate the birth prevalence of these conditions: maple syrup urine disease, homocystinuria (pyridoxine unresponsive), glutaric aciduria type I, isovaleric acidaemia and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency including trifunctional protein deficiency. We identified a total of 99 studies that were able to provide information on the prevalence of one or more of the disorders. The vast majority of studies were of screening programmes with some reporting on clinically detected cases.

[What disorders suspect following an increase of phenylalanine on newborn screening?]

Screening for PKU, in France, is made on the 3rd day of life by measuring the concentration of phenylalanine in dried blood spot samples. In this study, the goal was to examine the final diagnosis of patients who showed a hyperphenylalaninemia during newborn screening laboratory. Over a period of 11 years from 1 February 2002 to 31 January 2013, all newborns with a phenylalanine concentration increase (>180 μmol/L) have been identified and the cause of this increase was noted. Of the 165,113 newborns screened, hyperphenylalaninemia was identified in 90 patients during the newborn screening laboratory. During this period 35% of cases were due to classical phenylketonuria or hyperphenylalaninemia. In 4.4% of cases, increase concentrations were due to other diseases (biopterine deficiency, galactosemia, MSUD). However, 48.9% of high concentrations have not been confirmed by a second sample and 11% were children who died rapidely during their first days of life. The positive predictive value (PPV) of the test with a threshold of positivity >180 μmol/L was 40%. Our study showed that the positivity threshold of 180 μmol/L proposed by the Association française pour le dépistage et la prévention des handicaps de l'enfant (AFDPHE) provides a comprehensive detection of all phenylketonuria cases as well as mild hyperphenylalaninemia permanent and transient cases. Eventhough the use of a higher threshold would have the advantage of increasing the PPV of the test, none the less we would have missed out on some cases to follow.

Incidence of maple syrup urine disease in Portugal

Maple syrup urine disease is an autosomal recessive disorder of branched-chain amino acids metabolism with a worldwide frequency of 1/185,000 live newborns. In Portugal, the incidence of the disease has not been assessed. Based on the review of the cases diagnosed by tandem mass spectrometry an incidence of 1/86,800 live newborns was estimated in Portugal, indicating that the disease is more frequent in this country than reported in most populations.

Maple syrup urine disease in Thai infants

Maple syrup urine disease (MSUD) is a rare inborn error of metabolism, caused by a deficiency in activity of the branched chain alpha-keto acid dehydrogenase impairing the degradation of the branched-chain amino acids (leucine, isoleucine and valine). Classic MSUD usually manifests in the neonatal period with poor feeding, vomiting, lethargy, muscular hypertonicity, seizure, coma and death. Thirteen cases of classic MSUD were diagnosed from 1997-2007 at the Queen Sirikit National Institute of Child Health. All cases presented in the neonatal period. The onset of symptoms ranged from 3 to 20 days (median 8 days). The time taken to make the diagnosis ranged from 18 to 356 days (median 55 days). The diagnosis was accomplished by clinical diagnosis and confirmed by detecting abnormal levels of amino acids in the blood and organic acids in the urine. Clinical manifestations were non-specific such as poor suck, weak cry, drowsiness and seizures. Majority of cases were initially diagnosed as sepsis and/or meningitis. All patients had neurological sequelae and psychomotor retardation. This results show the need for increase awareness of metabolic disorder such as MSUD and the requirement for early detection and treatment to ensure a better outcome.

Mutational spectrum of maple syrup urine disease in Spain

Mutations in any of the three different genes BCKDHA, BCKDHB, and DBT encoding for the E1alpha, E1beta, and E2 catalytic components of the branched-chain alpha-ketoacid dehydrogenase (BCKD) complex can cause maple syrup urine disease (MSUD). The disease presents heterogeneous clinical and molecular phenotypes. Severity of the disease ranges from the classical to the mildest variant types. Here, we describe the MSUD genotypes and related phenotypes in a cohort of 33 Spanish patients. Based on complementation testing, we selected 15 patients as defective in E1beta, 10 in E1alpha, seven in E2l; one remains unclassified. 92.5% of alleles have been characterized, and the mutational spectrum includes 36 different sequence variations presumably leading to loss-of-function, 15 changes in the BCKDHA, 14 in the BCKDHB, and seven in the DBT genes. Twenty-four changes are novel. The mutational profile is heterogeneous with no prevalent sequence variations detected, except for the E1beta mutation, c.487G>T (p.Glu163X), which appears on six out of 30 disease alleles analyzed. Approximately 30% of the patients included in this study showed a variant MSUD phenotype. That included 50% of the patients identified as EIa and at least four out of seven of those selected as EII. Precise genotypes as c.[647C>T]+[889C>T] for the EIa and c.[827T>G ]+[1349C>A] for the EII appeared associated to the mildest presentations of the disease.

Maple syrup urine disease-treatment and outcome in patients of Turkish descent in Germany

Maple syrup urine disease (MSUD) is a rare autosomal recessive disorder that causes acute and chronic brain dysfunction because of a neurotoxic effect of the accumulating branched chain amino acids (BCAA) and their corresponding keto acids. Aim of the treatment is a rapid reversal of the neonatal decompensation and a stable long-term metabolic control obtained by a carefully adjusted BCAA-low diet. In optimally treated patients, an unimpaired neurological and intellectual outcome is possible. Ten patients of Turkish origin suffering from MSUD are presently treated in the Metabolic Unit of the University Hospital in Düsseldorf, Germany. All patients show mild intellectual deficits; neurological impairment is rare. This paper aims to define the feasible standard of therapy and the resulting intellectual and psychosocial outcome achievable in MSUD patients of Turkish origin under high standard conditions of medical care for inborn errors of metabolism.

Frequencies of inherited organic acidurias and disorders of mitochondrial fatty acid transport and oxidation in Germany

The lack of epidemiological data on the frequency and/or burden of organic acidurias (OA) and mitochondrial fatty acid transport and oxidation disorders (mtFATOD) is one reason for hesitation to expand newborn screening (NBS) by tandem mass spectrometry (MS-MS). From 1999 to 2000, the frequency of ten potentially treatable OA and mtFATOD was assessed by active nation-wide surveillance on cases presenting with clinical symptoms using the German Paediatric Surveillance Unit (ESPED) system. Case ascertainment was complemented by a second independent source: 3-monthly inquiries in the metabolic laboratories performing secondary selected screening for OA and mtFATOD. Frequency estimates for clinically symptomatic cases older than 7 days in a birth cohort of 844,575 conventionally screened children was compared to the frequency found in a cohort of 382,247 screened by MS-MS in Bavaria and Baden-Württemberg. The overall frequency of the ten conditions considered was 1:8,000 (95% CI 1:11,000-1:6,000) by MS-MS as compared to 1:23,000 (95% CI 1:36,000-1:17,000) in symptomatic cases presenting mainly with metabolic crisis. The contributions of medium-chain acyl-CoA dehydrogenase deficiency (MCADD), other mtFATOD and OA were 29, 4 and 13 among the 46 cases identified by MS-MS, and 19, 1 and 13 among the 33 clinically symptomatic cases, respectively. Acute metabolic crisis, with a lethal outcome in four patients, was reported for 22/33 clinically symptomatic cases. No clinically symptomatic cases were reported from cohorts with screened by MS-MS.

CONCLUSION

ten potentially treatable organic acidurias and mitochondrial fatty acid transport and oxidations disorders were more common than phenylketonuria with organic acidurias accounting for 28% of the cases detected by newborn screening and 39% of the cases identified on high risk screening. These conditions were related to considerable morbidity and mortality. Considerations for their inclusion in expanded newborn screening programmes might be warranted.

Selective screening of amino acid disorders in the south-west of Iran, Shiraz

A diagnostic study of amino acid concentrations in dried blood spot samples from 1044 symptomatic children revealed high incidences of phenylketonuria, tyrosinaemias, and maple syrup urine disease in the Shiraz region of Iran. Minimum incidences, based on babies born between 1996 and 2001 inclusive, and diagnosed by the end of 2001, are 1:3672, 1:10651 and 1:21 303, respectively.

Is demyelination a feature of maple syrup urine disease?

To determine whether disturbance of myelination is a pathophysiologic feature in patients with treated maple syrup urine disease (MSUD), neurophysiologic studies were performed in 10 MSUD patients ages 4-16 years. Afferent and efferent pathways were studied by visual evoked potentials, somatosensory evoked potentials, motor evoked potentials, stance-stabilizing reflexes, and peripheral nerve conduction velocity. Magnetic resonance imaging was used to detect possible cerebral white matter abnormalities. Visual evoked potentials were normal in all patients. There was only slight prolongation of central afferent and efferent conduction times and the long latency component of the stance-stabilizing reflexes. Peripheral nerve conduction studies revealed reduced sensory nerve conduction velocity in 3 patients. The neurophysiologic findings were not consistently correlated to the neurologic outcome of the patients. Magnetic resonance imaging did not reveal major abnormalities and demonstrated bilateral periventricular high intensity periventricular signals on T2-weighted images in 4 of 10 patients. It is concluded that dysmyelination is not a major pathophysiologic feature in patients with MSUD.

State screening for metabolic disorders in newborns

Most states have mandatory screening programs for congenital and inherited disorders of metabolism. Physicians may be unaware of their state's requirements, and compiled lists of testing requirements are generally unavailable or incomplete. All states test for congenital hypothyroidism and phenylketonuria. Some states require that newborns be tested for up to six other specific congenital and inherited disorders of metabolism. Some states base their decision to test on demographic data, but there is no uniformity in the tests.

Newborn metabolic screening: a search for "nature's experiments"

The rationale for metabolic screening includes discovery of new diseases, development of treatment methods, determination of the true incidence of disease in order to provide genetic counseling, and relief to the taxpayer when retardation is preventable. The number of diseases for which we can now screen is large and growing and must be periodically reviewed. Physical, cultural, and religious factors affect gene pool mixing, making it impossible to predict a priori what the incidence of a given disorder will be within the population screened. This paper reviews the rationale for establishing neonatal metabolic screening programs and the significance of the information gained.

Follow-up study of a nation-wide neonatal metabolic screening program in Japan. A collaborative study group of neonatal screening for inborn errors of metabolism in Japan

A nationwide neonatal screening program for phenylketonuria (PKU), maple syrup urine disease (MSUD), homocystinuria, histidinemia and galactosemia was started in Japan in 1977. The total number of infants screened had reached 6,311,754 by March, 1982. A follow-up study revealed the incidence of the disease in Japan: 1/108,823 for PKU; 1/450,840 for hyperphenylalaninemia (HPA); 1/1,577,939 for biopterin deficiency; 1/525,980 for MSUD; 1/1,051,959 for homocystinuria; 1/8,371 for histidinemia, and 1/788,969 for galactosemia type 1. The incidences of PKU, HPA, homocystinuria, and galactosemia (type 1) were found to be markedly low in Japan as compared with those in Caucasian countries. There was no great difference in the incidence of MSUD between both. On the other hand, the incidence of histidinemia was higher in Japan. It was found that most of the patients with PKU, HPA, MSUD, homocystinuria, or galactosemia are developing normally due to the early initiation of dietary treatment. These results clearly indicate that the neonatal mass screening program plays a great role in preventing the occurrence of handicapped children.

Geographical variations in inborn errors of metabolism in Japan

Using materials from a nationwide screening project on inborn errors of metabolism in Japan, the incidence of histidinemia, phenylketonuria, galactosemia and homocystinuria were found to be 140, 16, 14 and 7 in 1 million live births, respectively. Geographical variations were observed, especially in histidinemia, which are most likely due to chance.

Incidence of disorders tested by systematic screening: confidence limits and comparison of programmes

Using the data from screening done in Switzerland since 1965, we showed that the probability of finding cases with increased phenylalanine or leucine concentrations is compatible with a Poisson distribution. If there are no trends present from year to year and if the Poisson distribution is an accurate fit further statistical treatment is possible. The advantage of using the Poisson distribution is exemplified by the calculation of confidence limits for the incidence of hyperphenylalaninaemia, maple syrup urine disease and hypothyroidism. Furthermore, statistical comparisons between different screening programs are easily done.

Newborn screening for maple syrup urine disease (branched-chain ketoaciduria)

Routine newborn screening for maple syrup urine disease (MSUD) has been conducted since 1964, and more than 9 1/2 million newborns throughout the world have been tested with use of a bacterial inhibition assay (BIA) for leucine on dried filter paper blood specimens. Forty-three confirmed cases of the "classical" and the "intermediate" variant forms have been detected. The frequency of MSUD, based on these data, is approximately one in 224,000 newborns. The sensitivity and the specificity of the leucine BIA are demonstrated. There are several problems in routine screening for MSUD, including the fact that the "intermittent" variant form will be missed. A brief summary of the clinical course of the 13 cases detected by our collaborative laboratories is presented.

Inborn errors of metabolism in the Maritimes, with special reference to maple-syrup-urine disease and Fabry's disease

1. The study of inborn errors of metabolism in man is of wide, general relevance to human biology and medicine, because these derangements are unique human models for the study of the sequence of normal metabolic events and their dependence upon genetic control. These disorders constitute naturally occurring mutations in man; as such, they afford the same opportunity for major contributions to human biology that bacterial mutants provide for molecular biology. 2. In terms of human suffering and cost, to affected kindred and the community at large, the importance of inborn errors of metabolism is out of all proportion to their small numerical incidence. Therefore, efforts must be intensified to identify affected individuals and carriers and to formulate methods of prevention and treatment. 3. The overall study of inborn errors of metabolism is illustrated by experience with two such disorders in the Maritime provinces.