Neonatal screening in Italy for congenital hypothyroidism and metabolic disorders: hyperphenylalaninemia, maple syrup urine disease and homocystinuria

Birth prevalence of phenylalanine hydroxylase deficiency: a systematic literature review and meta-analysis

BACKGROUND

Phenylalanine hydroxylase (PAH) deficiency is an autosomal recessive disorder that results in elevated concentrations of phenylalanine (Phe) in the blood. If left untreated, the accumulation of Phe can result in profound neurocognitive disability. The objective of this systematic literature review and meta-analysis was to estimate the global birth prevalence of PAH deficiency from newborn screening studies and to estimate regional differences, overall and for various clinically relevant Phe cutoff values used in confirmatory testing.

METHODS

The protocol for this literature review was registered with PROSPERO (International prospective register of systematic reviews). Pubmed and Embase database searches were used to identify studies that reported the birth prevalence of PAH deficiency. Only studies including numeric birth prevalence reports of confirmed PAH deficiency were included.

RESULTS

From the 85 publications included in the review, 238 birth prevalence estimates were extracted. After excluding prevalence estimates that did not meet quality assessment criteria or because of temporal and regional overlap, estimates from 45 publications were included in the meta-analysis. The global birth prevalence of PAH deficiency, estimated by weighting regional birth prevalences relative to their share of the population of all regions included in the study, was 0.64 (95% confidence interval [CI] 0.53-0.75) per 10,000 births and ranged from 0.03 (95% CI 0.02-0.05) per 10,000 births in Southeast Asia to 1.18 (95% CI 0.64-1.87) per 10,000 births in the Middle East/North Africa. Regionally weighted global birth prevalences per 10,000 births by confirmatory test Phe cutoff values were 0.96 (95% CI 0.50-1.42) for the Phe cutoff value of 360 ± 100 µmol/L; 0.50 (95% CI 0.37-0.64) for the Phe cutoff value of 600 ± 100 µmol/L; and 0.30 (95% CI 0.20-0.40) for the Phe cutoff value of 1200 ± 200 µmol/L.

CONCLUSIONS

Substantial regional variation in the birth prevalence of PAH deficiency was observed in this systematic literature review and meta-analysis of published evidence from newborn screening. The precision of the prevalence estimates is limited by relatively small sample sizes, despite widespread and longstanding newborn screening in much of the world.

Worldwide Recall Rate in Newborn Screening Programs for Congenital Hypothyroidism

CONTEXT

Neonatal mass screening program for congenital hypothyroidism provides the best tool for prevention of its devastating effects on mental development. Despite the overall success of the screening programs in detecting congenital hypothyroidism and eliminating its sequelae and new developments made in the program design, high recall rate and false positive results impose a great challenge worldwide. Lower recall rate and false positive results may properly organize project expenses by reducing the unnecessary repeated laboratory tests, increase physicians and parents' assurance and cooperation, as well as reduce the psychological effects in families.

EVIDENCE ACQUISITION

In this review, we assessed the recall rate in different programs and its risk factors worldwide.

METHODS

Publications reporting the results of the CH screening program from 1997 to 2016 focusing on the recall rate have been searched.

RESULTS

Recall rates vary from 0.01% to 13.3% in different programs; this wide range may be due to different protocols of screening (use of T4 or TSH or both), different laboratory techniques, site of sample collection, recall cutoff, iodine status, human error, and even CH incidence as affected by social, cultural, and regional factors of the population.

CONCLUSIONS

It is suggested to implement suitable interventions to reduce the contributing factors by improving the quality of laboratory tests, selecting conservative cut off points, control iodine deficiency, use of iodine free antiseptic during delivery, and use of more specific markers or molecular tests. Applying an age dependent criteria for thyrotropin levels can be helpful in regions with a varied time of discharge after delivery or for preterm babies.

An Assessment of Dried Blood-Spot Technology for Identifying Iron Deficiency

The present study was undertaken to assess the feasibility of using ferritin and transferrin receptor measurements on dried capillary blood spots to identify iron deficiency (ID) in public health surveys. Measurements on serum and blood spots prepared from venous blood were performed in 71 healthy subjects, 41 of whom were iron-replete and 30 who had ID, either without (n = 20) or with (n = 10) anemia. Parallel measurements were performed on hemolyzed whole blood and washed hemolyzed red blood cells to assess the erythrocyte contribution of ferritin and transferrin receptor to dried blood samples. The concentration of ferritin in dried blood samples was threefold higher than serum assays due to the release of ferritin from hemolyzed erythrocytes, which diminished the usefulness of ferritin measurements for detecting ID. On the other hand, there was negligible erythrocyte contribution to the measurement of transferrin receptor in dried blood spots. The most sensitive parameter in dried blood spots was the ratio of receptor/ferritin, which was suitable for identifying iron-deficiency anemia (IDA), but less reliable than serum assays for detecting milder ID without anemia. We conclude that tandem measurements of serum ferritin and transferrin receptor in dried blood spots can be used to facilitate the identification of IDA in epidemiologic studies.

© 1998 by The American Society of Hematology.

An Assessment of Dried Blood-Spot Technology for Identifying Iron Deficiency

The present study was undertaken to assess the feasibility of using ferritin and transferrin receptor measurements on dried capillary blood spots to identify iron deficiency (ID) in public health surveys. Measurements on serum and blood spots prepared from venous blood were performed in 71 healthy subjects, 41 of whom were iron-replete and 30 who had ID, either without (n = 20) or with (n = 10) anemia. Parallel measurements were performed on hemolyzed whole blood and washed hemolyzed red blood cells to assess the erythrocyte contribution of ferritin and transferrin receptor to dried blood samples. The concentration of ferritin in dried blood samples was threefold higher than serum assays due to the release of ferritin from hemolyzed erythrocytes, which diminished the usefulness of ferritin measurements for detecting ID. On the other hand, there was negligible erythrocyte contribution to the measurement of transferrin receptor in dried blood spots. The most sensitive parameter in dried blood spots was the ratio of receptor/ferritin, which was suitable for identifying iron-deficiency anemia (IDA), but less reliable than serum assays for detecting milder ID without anemia. We conclude that tandem measurements of serum ferritin and transferrin receptor in dried blood spots can be used to facilitate the identification of IDA in epidemiologic studies.

© 1998 by The American Society of Hematology.

Evolution of daytime quiet sleep components in early treated phenylketonuric infants

The maturational patterns of 'tracé alternant' (TA) and sleep spindles obtained from 16 early detected phenylketonuric (PKU) children during their first months of life were compared with others that were evaluated in recordings taken from 42 controls of the same age group. The TA maturation evolved significantly later in the PKU group than in the control group during the 5th-8th week (the TA score for the PKU group was 64% vs. 10% in the control group, P < 0.001). Afterwards, during the 9th-12th week the score for the PKU group was 27% vs. 0% in the controls (P < 0.002). The sleep spindle evolution score also matured significantly later in the PKU than the control group: the score was 31% in PKU children vs. 85% in controls for the 5th-8th week of age (P < 0.01), and it was 66% vs. 96% for the 9th-12th week (P < 0.02). After the 12th week, TA pattern could not be detected, and spindles reached complete maturation in the PKU children as well. Our results show a consistent delay in the maturation of TA and spindle scores in PKU children. This trend of delay is parallel to the plasma phenylalanine normalization, but not necessarily dependent only on it. In conclusion, we suggest that studies on the critical maturational periods of different sleep components (TA and sleep spindles) might provide a sensitive tool for early diagnosis of neurophysiological brain alterations during the first trimester of life in a population of children "at risk'.

The development of auditory and visual evoked potentials in early treated phenylketonuric children

Brain-stem auditory evoked potentials (BAEPs) and flash visual evoked potentials (F-VEPs) were gathered from 8 early treated phenylketonuric (PKU) children in a prospective longitudinal investigation during the 1st to the 12th months after birth. No consistent differences were found in the wave morphology of evoked potentials in PKU children from that of age-matched controls. Studying the latency of some components showed that in BAEPs, wave I latency was similar to control values for the whole year, but that the I-V interpeak mean latency (I-V IPL) was always significantly longer than in controls. In F-VEPs wave N1 latency was significantly longer than in controls only at 1-2 months of age, but returned to control values at 3-4 months (when all children were on dietary therapy) and remained in this range up to the 12th month. The mean latency of the P2 wave of flash VEPs was always significantly longer in PKU children than in controls. These results show that relevant alterations in evoked potentials may be found in PKU children several months after starting dietary therapy. This suggests that information processing in the brain may be impaired for a long time, due to abnormal metabolic conditions between birth and the onset of dietary therapy.

Simultaneous high-performance liquid chromatographic determination of amino acids in a dried blood spot as a neonatal screening test

A new screening test on dried blood spots for inherited disorders of amino acid metabolism using reversed-phase high-performance liquid chromatography (RP-HPLC) is described. The method allows the simultaneous analysis of fourteen different amino acids; among these, seven whose blood levels are increased in the most important amino acid disorders have been determined. The procedure requires a preliminary extraction of the amino acids from 9-mm autoclaved dried blood spots by sonication in phosphate-buffered saline. A precolumn o-phthaldialdehyde-3-mercaptopropionic acid derivatization is then followed by analysis of the amino acids by RP-HPLC. Blood-spots levels of histidine (His), tyrosine (Tyr), valine (Val), methionine (Met), isoleucine (Ile), phenylalanine (Phe) and leucine (Leu) can be determined in a single 15-min run, including column washing and regeneration. The minimum detectable amount of each amino acid is 0.5 pmol with a linear dose-response range between 1 and 10 microM. The recovery for all amino acids is greater than 70% except for Met (66%). Up to 20,000 samples/year can be processed on a single automated analytical line resulting in an estimated cost of about US$ 0.25/sample. The multiple diagnostic capacity, the low cost and the possibility of complete automation of the method make it suitable for primary perinatal screening of amino acid disorders.

EEG as a possible prognostic tool in phenylketonuria

Clinical EEG and biochemical data were recorded in 10 children with classical PKU and 5 with variant forms of hyperphenylalaninaemias during the first year of life. A semiquantitative evaluation of the EEG showed a high correlation between epileptiform abnormalities and phenylalanine blood levels in the first 90 days of life and therefore with the delay before dietary therapy in PKU children. Although performed on a limited population, such an approach may indicate an additional non-computerized EEG tool for the clinical management of hyperphenylalaninaemias, and suggest some criteria for neurophysiological risk evaluation during the first year of life.

Immunoreactive trypsin on dried-blood spots as a possible neonatal test for cystic fibrosis. (I. Evaluation of the method and preliminary field trial)

A method for blood spot immunoreactive trypsin (IRT) determination suitable for neonatal mass screening, and the preliminary steps towards its large-scale application are described. The method showed a highly significant correlation between blood spot and plasma values, and a study of plasma reference values in a population of 1,050 newborn infants demonstrated a log-normal distribution with a mean IRT concentration of 238.3 ng/ml. The results and their implications for neonatal mass screening are discussed.