The use of dried blood spot samples in the diagnosis of lysosomal storage disorders--current status and perspectives.

Dried blood spot (DBS) methods are currently available for identification of a range of lysosomal storage disorders (LSDs). These disorders are generally characterized by a deficiency of activity of a lysosomal enzyme and by a broad spectrum of phenotypes. Diagnosis of LSD patients is often delayed, which is of particular concern as therapeutic outcomes (e.g. enzyme replacement therapy) are generally more favorable in early disease stages. Experts in the field of LSDs diagnostics and screening programs convened and reviewed experiences with the use of DBS methods, and discuss the diagnostic challenges, possible applications and quality programs in this paper. Given the easy sampling and shipping and stability of samples, DBS has evident advantages over other laboratory methods and can be particularly helpful in the early identification of affected LSD patients through neonatal screening, high-risk population screening or family screening.

Low levels of asymmetric dimethylarginine in children with diabetes mellitus type I compared with healthy children.

OBJECTIVE: Although high levels of asymmetric dimethylarginine (ADMA) are associated with an increased risk for vasculopathy in adults, elevated ADMA concentrations also have been found in healthy young children. Patients with diabetes mellitus type 1 (DM1) are at risk for vasculopathy, and because the function of ADMA in the development of vascular symptoms is incompletely understood, we investigated ADMA concentrations in pediatric patients with DM1 compared with healthy age- and sex-matched individuals. STUDY DESIGN: This cross-sectional study included 85 pediatric patients with DM1 and 89 age- and sex-matched healthy controls. RESULTS: ADMA concentrations were significantly lower in the patients with DM1 and were inversely correlated with hemoglobin A1c concentrations. CONCLUSIONS: Besides its vasoprotective function, nitric oxide itself may exert oxidative stress by generating free radicals. In these circumstances, ADMA would protect the system from nitric oxide overproduction and perpetuation of oxidative stress. This theory is supported by the physiologically higher ADMA concentrations in healthy children. Thus, low ADMA concentrations in children with DM1 may be an indicator of impaired protection against oxidative stress.

The identification of novel mutations in the biotinidase gene using denaturing high pressure liquid chromatography (dHPLC).

Biotinidase deficiency (BD) is an autosomal recessive disorder of biotin metabolism that causes incomplete recycling of free biotin. The resulting depletion of intracellular biotin leads to impaired activities of biotin-dependent carboxylases. The ensuing clinical phenotype includes progressive neurologic deterioration with epileptic seizures, muscular hypotonia as well as skin eczema. BD may be readily diagnosed by analysing enzyme activity in dried blood spots during newborn screening but typically requires molecular confirmation. More than 100 different mutations in the biotinidase gene have been reported to date. To simplify molecular testing we have developed a rapid and accurate denaturing high pressure liquid chromatography (dHPLC) method of the promoter, 3'UTR, all exons including exon/intron boundaries as a first line screen followed by direct sequencing of the respective PCR products. To validate this method we used DNA from 23 different, newly diagnosed patients with biochemically proven BD from Austria, India, Morocco and Spain. A total of 11 mutations, missense 7, frameshift 3 and 1 nonsense, were screened. Six mutations were novel to this study. All mutations revealed distinct dHPLC pattern thus enabling their accurate detection. This study revealed that dHPLC method is robust, automated, economical and above all highly sensitive for the molecular analysis of biotinidase gene and should be used as a pre-analytical tool followed by sequencing of aberrant heteroduplex forming amplicons.

Development and evaluation of quality control dried blood spot materials in newborn screening for lysosomal storage disorders.

BACKGROUND: Lysosomal storage disorders (LSDs) comprise more than 40 genetic diseases that result in the accumulation of products that would normally be degraded by lysosomal enzymes. A tandem mass spectrometry (MS/MS)-based method is available for newborn screening for 5 LSDs, and many laboratories are initiating pilot studies to evaluate the incorporation of this method into their screening panels. We developed and evaluated dried blood spot (DBS) QC materials for LSDs and used the MS/MS method to investigate their suitability for LSD QC monitoring. METHODS: We incubated 3.2-mm punches from DBS controls for 20-24 h with assay cocktails containing substrate and internal standard. Using MS/MS, we quantified the resulting product and internal standard. Samples were run in triplicate for 3 consecutive days, and results were reported as product-to-internal standard ratios and enzyme activity units (micromol/L/h). RESULTS: Enzyme activity interday imprecision (CV) for the high, medium, and low series were 3.4%-14.3% for galactocerebroside alpha-galactosidase, 6.8%-24.6% for acid alpha-galactosidase A, 7.36%-22.1% for acid sphingomyelinase, 6.2%-26.2% for acid alpha-glucocerebrosidase, and 7.0%-24.8% for lysosomal acid alpha-glucosidase (n = 9). In addition, DBS stored at -20 degrees and 4 degrees C showed minimal enzyme activity loss over a 187-d period. DBS stored at 37 degrees and 45 degrees C had lower activity values over the 187-day evaluation time. CONCLUSIONS: Suitable QC materials for newborn screening of LSDs were developed for laboratories performing DBS LSD screening. Good material linearity was observed, with goodness-of-fit values of 0.953 and higher. The QC materials may be used by screening laboratories that perform LSD analysis by MS and/or more conventional fluorescence-based screening methods.

Transcobalamin II deficiency at birth.

Transcobalamin II deficiency (# MIM 275350) is a rare, recessively inherited disorder of cobalamin transport that leads to intracellular cobalamin depletion with secondary impairment of methionine synthetase and methyl-malonyl CoA mutase activities. Affected individuals may suffer from long-term neurological sequelae if therapy with intramuscular hydroxocobalamin is not initiated promptly. We report two sisters with complete absence of transcobalamin due to homozygosity for a novel mutation (c.insC110) in the TCN2 gene that leads to a premature stop codon and non-functional protein. The older sister, now 4.5 years old, presented at 6 weeks of age with pancytopenia, protein losing enteropathy and a rapidly declining clinical course. Prompt therapy with 1mg hydroxocobalamin/day led to full recovery within days. Her now 1.5 year old sister was diagnosed shortly after birth and was started on hydroxocobalamin prior to onset of clinical symptoms. Interestingly, urinary methylmalonic acid excretion was increased significantly during the first days of life suggesting that functional cobalamin deficiency is present also during fetal life, although not giving rise to clinical symptoms until well after birth.

Newborn screening for Pompe disease by measuring acid alpha-glucosidase activity using tandem mass spectrometry.

BACKGROUND: Pompe disease, caused by the deficiency of acid alpha-glucosidase (GAA), is a lysosomal storage disorder that manifests itself in its most severe form within the first months of life. Early detection by newborn screening is warranted, since prompt initiation of enzyme replacement therapy may improve morbidity and mortality. We evaluated a tandem mass spectrometry (MS/MS) method to measure GAA activity for newborn screening for Pompe disease. METHODS: We incubated 3.2-mm punches from dried blood spots (DBS) for 22 h with the substrate [7-benzoylamino-heptyl)-{2-[4-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydro-pyran-2-yloxy)-phenylcarbamoyl]- ethyl}-carbamic acid tert-butyl ester] and internal standard [7-d(5)-benzoylamino-heptyl)-[2-(4-hydroxy-phenylcarbamoyl)-ethyl]-carbamic acid tertbutyl ester]. We quantified the resulting product and internal standard using MS/MS. We assessed inter- and intrarun imprecision, carryover, stability, and correlation between enzyme activities and hematocrit and punch location and generated a Pompe disease-specific cutoff value using routine newborn screening samples. RESULTS: GAA activities in DBS from 29 known Pompe patients were <2 micromol/h/L. GAA activities in routine newborn screening samples were [mean (SD)] 14.7 (7.2) micromol/h/L (n = 10,279, median 13.3, 95% CI 14.46-14.74 micromol/h/L) and in normal adult samples 9.3 (3.3) micromol/h/L (n = 229, median 9, 95% CI 8.88-9.72 micromol/h/L). GAA activity was stable for 28 days between 37 degrees C and -80 degrees C. Carryover could not be observed, whereas intrarun and interrun imprecision were <10%. The limit of detection was 0.26 micromol/h/L and limit of quantification 0.35 micromol/h/L. CONCLUSIONS: The measurement of GAA activities in dry blood spots using MS/MS is suitable for high-throughput analysis and newborn screening for Pompe disease.

Total homocysteine, B-vitamins and genetic polymorphisms in patients with classical phenylketonuria.

Hyperhomocysteinemia has occasionally been reported in patients with phenylketonuria (PKU) and B-vitamin deficiency. In our study total homocysteine (tHcy) and B-vitamins were measured in treated PKU patients and healthy controls. In the patients, dietary parameters and genetic polymorphisms affecting the Hcy pathway were investigated to identify parameters modulating tHcy. A case control study including 37 PKU patients and 63 healthy controls was conducted. t-Tests for independent samples were used to test between groups. Multiple regressions with tHcy as dependent variable were calculated. Hardy-Weinberg expectations were tested against the observed distribution of genotypes applying the Chi-square goodness-of-fit method. THcy concentrations were not significantly different (p=0.059) while folate and cobalamin (Cbl) concentrations were significantly higher in PKU patients compared to controls. However, 29.7% of patients had tHcy concentrations >97th centile. THcy did not vary with age nor correlate with folate and Cbl concentrations probably due to high saturatory levels. The presence of genetic polymorphisms had no impact on tHcy. In conclusion, in PKU patients treated with amino acid mixtures enriched with B-vitamins, tHcy is not significantly higher than in healthy controls, but tHcy concentrations exceed the 97th centile in about one third of patients. Even higher B-vitamin saturation may be required to further decrease tHcy concentrations and factors generally influencing tHcy such as betaine are to be investigated in PKU patients in the future.

The main components of St John's Wort inhibit low-density lipoprotein atherogenic modification: a beneficial "side effect" of an OTC antidepressant drug?

Hypericin and pseudohypericin are polycyclic-phenolic structurally related compounds found in Hypericum perforatum L. (St John's wort). As hypericin has been found to bind to LDL one may assume that it can act as antioxidant of LDL lipid oxidation, a property which is of prophylactic/therapeutic interest regarding atherogenesis as LDL oxidation may play a pivotal role in the onset of atherosclerosis. Therefore, in the present paper hypericin, pseudohypericin and hyperforin, an other structurally unrelated constituent in St John's wort were tested in their ability to inhibit LDL oxidation. LDL was isolated by ultracentrifugation and oxidation was initiated either by transition metal ions (copper), tyrosyl radical (myeloperoxidase/hydrogen peroxide/tyrosine) or by endothelial cells (HUVEC). LDL modification was monitored by conjugated diene and malondialdehyde formation. The data show that all compounds (hypericin, pseudohypericin and hyperforin) at doses as low as 2.5 micromol/l are potent antioxidants in the LDL oxidation systems used. The results indicate that the derivatives found in Hypericum perforatum have possible antiatherogenic potential.

Influence of hematocrit and localisation of punch in dried blood spots on levels of amino acids and acylcarnitines measured by tandem mass spectrometry.

BACKGROUND: Detection of amino acids (AA), acylcarnitines (AC), and guanidinoacetate (GAA) in dried blood spots by tandem mass spectrometry has made it possible to detect different inborn errors of metabolism in neonatal screening programs. Despite its proven sensitivity many issues related to sample preparation remain unsolved. Hematocrit has a profound effect on blood viscosity, and may thereby influence flux and diffusion properties of the blood. As newborn infants show a considerable interindividual variability of hematocrit levels, we investigated its effect on levels of AA and AC in dried blood spots. METHODS: Blood samples with defined hematocrit levels (20%, 30%, 40%, 50%, 60%) were produced by diluting blood cells with plasma from a single donor. Forty dried blood spots were made for each hematocrit level and a central as well as a peripheral 3 mm disk was punched and analysed for AA, AC, and GAA, respectively. RESULTS: Levels of most AA and GAA increased significantly with increasing hematocrit (p<0.001), while the effect of hematocrit on some AA was less pronounced. Total AC, free carnitine, some long, medium and short chain AC correlated positively with hematocrit levels (p<0.001). In samples with low hematocrit, levels of most AA and free carnitine were higher in the peripheral than in the central disk (p<0.0001). CONCLUSIONS: Both hematocrit and position of the disk within the dried blood spot have a significant and sometimes additive effect on levels of AA, AC and GAA in dried blood spots. Theoretically, diagnoses may be missed depending on hematocrit and position of the disk.

Bridging to transplantation in acute liver failure in a 7-month-old infant.

BACKGROUND: Acute liver failure (ALF) in children is a rare but often fatal event. At present, liver transplantation is the only successful therapy in most cases. In the face of deteriorating hepatic encephalopathy in these children, some bridging therapy using artificial detoxification can be necessary to enable successful transplantation. In adults, albumin dialysis using the molecular absorbent recycling system (MARS) has been described as effective for bridging to liver transplantation. CASE REPORT: A previously healthy 7-month-old infant was admitted with ALF due to autoimmune hepatitis. King's College criteria for children with ALF indicated the need for transplantation (bilirubin 13.7 mg/dl, leukocytes 18,980/mm3, INR 5.83, age<2 years). Despite moderate hyperammonemia (75 microm/l) along with the development of pneumonia, the child deteriorated hemodynamically and neurologically, showing grade III encephalopathy proven by EEG. Albumin dialysis using MARS was used to bridge 36 hours to successful living-donor split-liver transplantation, and resulted in improvements in EEG, plasma levels of amino acids and hemodynamics. Twenty-four months after transplantation the child shows normal liver function and normal neuropsychological development. The explanted liver showed 80 % tissue destruction from autoimmune hepatitis. CONCLUSION: Albumin dialysis as described can be used successfully in infants < 1 year old for bridging to liver transplantation in cases of acute hepatic failure with deteriorating encephalopathy.

Rapid analysis of total plasma homocysteine by tandem mass spectrometry.

Elevated plasma homocysteine levels may be an independent risk factor for premature vascular disease. Early detection and population screening are warranted to recognise hyperhomocysteinemia and initiate homocysteine lowering therapy. Current methods for homocysteine analysis are time consuming, labor intensive and/or expensive. We developed a sensitive and fast method for homocysteine analysis based on tandem mass spectrometry that avoids the need for derivatization and preanalytical chromatography.

Analysis of acid sphingomyelinase activity in dried blood spots using tandem mass spectrometry.

BACKGROUND: Niemann Pick disease (NP) is a rare, lysosomal storage disorder due to deficiency of the intra-lysosomal enzyme acid sphingomyelinase (ASM) resulting in intracellular accumulation of sphingomyelin. We evaluated a tandem mass spectrometry (MS/MS) method to analyze ASM activity in dried blood spots (DBS) that may be suitable for laboratory diagnosis of NP including high throughput screening of at-risk populations and potentially for newborn screening. METHODS: ASM activity was measured in 3.2 mm punches from DBS. The eluate was incubated with the ASM substrate (N-Hexanoyl-D-erythro-sphingosylphosphorylcholine [C6-sphingomyelin (C(29)H(59)N(2)O(6)P)]) and an internal standard (N-butyroyl-D-erythro-sphingosine [C4-ceramide (C(22)H(43)NO(3))]). ASM product and IS were analyzed using MS/MS in multiple reaction monitoring mode for transitions m/z 370.6>264.3 (ASM internal standard) and m/z 398.6>264.3 (ASM product). RESULTS: ASM activities were stable for up to 2 months at or below 4℃. Position of the punch in the DBS and/or hematocrit of the DBS had a limited effect on ASM activities. Both intra- and inter-assay variability were below 10%. There was no carry-over. The median ASM activity in 2,085 newborn infants was 9.5 µmol/h/L (mean 10.6) with a SD of 5.06 µmol/h/L. Six of 2,085 (0.3%) infants were found to have ASM activities below the cut-off of 2.5 µmol/h/L. ASM activities were below the cut-off level in all 10 previously diagnosed cases with NP (range: 0.16 to 2.08 µmol/h/L). CONCLUSIONS: This MS/MS method for the measurement of ASM activity in DBS is robust and suitable for laboratory diagnosis of NP.

Newborn screening for lysosomal storage disorders in hungary.

Even though lysosomal storage disorders (LSDs) are considered to be orphan diseases, they pose a highly relevant cause for morbidity and mortality as their cumulative prevalence is estimated to be 1:4,000. This is especially important as treatment in form of enzyme replacement therapy, substrate reduction therapy or stem cell transplantation is amenable for some LSDs. It is plausible that an early start of treatment might improve the overall prognosis and, even more important, prevent irreversible damage of key organs. To get a more precise insight into the real frequency of some LSDs in the general population, we screened 40,024 samples from the Hungarian newborn screening (NBS) program in Szeged for Fabry disease (FD), Gaucher disease (GD), Pompe disease (PD), and Niemann-Pick A/B (NPB) disease using tandem mass spectrometry. Altogether, 663 samples (1.66%) were submitted for retesting. Genetic confirmation was carried out for 120 samples with abnormal screening results after retesting, which identified three cases of GD, three cases of FD, nine cases of PD, and two cases with NPB. In some cases, we detected up to now unknown mutations - one in NPB and seven in PD - which raise questions about the clinical consequences of a NBS in the sense of late-onset manifestations. Overall, we conclude that screening for LSDs by tandem MS/MS followed by a genetic workup in identified patients is a robust, easy, valid, and feasible technology in newborn screening programs. Furthermore, early diagnosis of LSDs gives a chance to early treatment, but needs more clinical long-term data especially regarding the consequence of private mutations.

Effects of creatine supplementation in Rett syndrome: a randomized, placebo-controlled trial.

OBJECTIVE: To evaluate the effects of creatine monohydrate (CMH) supplementation on global DNA methylation and disease-specific clinical symptoms in female patients with Rett syndrome (RTT). METHODS: Double-blind, randomized, placebo-controlled crossover trial of female patients with RTT. Participants received 200 mg/kg of either CMH or placebo daily for 6 months and switched following a 4-week washout period. Primary endpoints were change in global DNA methylation and in a RTT-specific symptom score as defined by medical history and clinical evaluation with Rett Syndrome Motor and Behavioral Assessment. Secondary endpoints were changes in biochemical markers of methionine metabolism. RESULTS: Eighteen female patients aged 3 to 25 years with clinically diagnosed typical RTT and MECP2 mutation at clinical Stages III or IV were studied. CMH supplementation resulted in a statistically significant increase of global methylation by 0.11 (95% confidence interval 0.03-0.19, p = .009) compared with placebo. Total and subscores of Rett Syndrome Motor and Behavioral Assessment tended to improve but without statistical significance. CONCLUSION: CMH supplementation increases global DNA methylation statistically significantly. Scores were lower for creatine than for placebo reflecting clinical improvement but not reaching statistical significance. Biochemical variables of methionine-homocysteine remethylation are unaffected. Multicenter studies are urgently warranted to evaluate the long-term effects of CMH supplementation in an optimally homogenous RTT population over a prolonged period.

Analysis of glucocerebrosidase activity in dry blood spots using tandem mass spectrometry.

BACKGROUND: Gaucher disease (GD) is due to deficiency of acid-ß-glucosidase (ABG) and comprises a clinical spectrum with variable age of onset and severity. We evaluated a tandem mass spectrometry (MS/MS) method to measure ABG activity for high through-put screening. METHODS: ABG activity was measured in 3.2 mm punches from dry blood spots (DBS). Each punch was incubated for 21 h with the substrate D-Glucosyl-ß1-1'-N-dodecanoyl-D-erythro-sphingosine [C12-glucocerebroside (C(36)H(69)NO(8))] and internal standard N-myristoyl-D-erythro-sphingosine [C14-ceramide (C(32)H(63)NO(3))]. The product and internal standard were quantified using MS/MS. RESULTS: ABG activities in anonymized newborn screening samples from NY State were (mean) 22.0 µmol/h/L±(SD) 13.8 µmol/h/L (n=2088, median 19.9 µmol/h/L, 95%CI 22.59-21.41 µmol/h/L). The enzymatic activity in DBS from 10 treatment naïve adult Gaucher patients was less than 4.2 µmol/h/L. ABG activity was stable for 3 months at room temperature a 20% activity reduction was observed. Inter- and intra-run imprecisions were 8% and 13.7%, respectively. The limit of detection was 0.75 µmol/h/L and limit of quantification was 1.25 µmol/h/L. CONCLUSIONS: The measurement of ABG activities in DBS using MS/MS is suitable for high-throughput analysis of at-risk individuals and potentially for newborn screening for GD.

Newborn screening for Fabry disease by measuring GLA activity using tandem mass spectrometry.

BACKGROUND: Fabry disease (FD) is an X-linked lysosomal storage disorder caused by the deficiency of alpha-galactosidase A (GLA). We evaluated a tandem mass spectrometry method to measure GLA activity. METHODS: One 3.2mm punch from a dried blood spot sample (DBS) was incubated with substrate and internal standard in the reaction buffer for 22 h. The resulting product was quantified against internal standard using MS/MS. RESULTS: The median GLA activity of male newborn DBS (N=5025) was 9.85 + or - 6.4 micromol/h/l (CI 95% is 9.67-10.02 micromol/h/l); The median GLA activity of female newborns (N=4677) was 10.2 + or - 6.3 micromol/h/l (CI 95% is 10.02-10.38 micromol/h/l). The difference between the two subgroups is within assay analytical variation. The GLA activities in the DBS samples from 9 juvenile and adult males with previously identified FD were below 1.64 micromol/h/l. The GLA activities from 32 juvenile and adult females with confirmed FD were below 4.73 micromol/h/l. In 5 (16%) females GLA activities were above the 0.5th percentile of lower limit of CI 95% at 3.18 micromol/h/l. CONCLUSIONS: The MS/MS method for Fabry disease newborn screening is robust and can be readily multiplexed with other lysosomal disorders such as Pompe, Gaucher, Niemann-Pick, and Krabbe diseases.

Manifestation of hawkinsinuria in a patient compound heterozygous for hawkinsinuria and tyrosinemia III.

Mutations in the gene for 4-hydroxyphenylpyruvic acid dioxygenase (HPD) cause either autosomal recessive tyrosinemia type III or autosomal dominant hawkinsinuria. We report a 6-month-old Indian infant who is compound heterozygous for both alleles and who has hawkinsinuria but not tyrosinemia type III based on biochemical investigations. The HPD gene was directly sequenced in the proband and both parents. The mechanistic model of the enzymatic function was built using the known structure of rat HPD. We identified a novel hawkinsinuria mutation, Asn241Ser, and a known tyrosinemia type III mutation, Ile335Met, in trans configuration. The structural analysis of the active site revealed that the IIe335Met mutation is situated in the close vicinity of one of the two highly conserved Phe rings which stack with the phenol ring of the substrate. The Asn241Ser mutation is situated further away from the 4-hydroxyphenylpyruvate binding pocket. Assuming that Asn241Ser causes hawkinsinuria, we propose positioning the dioxygen molecule in the HPD-catalyzed reaction as a novel role for the Asn residue. The IIe335Met allele is equivalent to a null mutation while the Asn241Ser allele results in a partially active enzyme with an uncoupled turnover causing hawkinsinuria.

Prevalence of congenital adrenal hyperplasia among sudden infant death in the Czech Republic and Austria.

This study aimed to estimate the number of infants who died of unrecognized congenital adrenal hyperplasia (CAH) in Austria and the Czech Republic within the past 13 years, before the introduction of adequate neonatal screening. The study was based on retrospective analysis of neonatal screening cards of 242 infants who died suddenly between 7 days and 12 months of age and whose cause of death could not be identified. 17-hydroxyprogesterone (17-OHP) was measured by fluoroimmunoassay and positive samples were subsequently genotyped. Three infants out of 242 may have had unrecognized CAH due to CYP21 (steroid 21-hydroxylase) gene defect. Their newborn 17-OHP levels and CYP21 genotypes were 706 nmol/l and del/conv//del/conv, 53 nmol/l and I2//I2, and 811 nmol/l and I2//Gln318stop, respectively. CAH due to CYP21 defect can lead to sudden unexpected death without prior symptoms typical for the condition. Hence, newborn screening would have prevented these deaths had it been available. In addition, we have shown that the I2 point mutation that is expected to lead to simple virilizing form may lead to a fatal outcome.

Long-term stability of amino acids and acylcarnitines in dried blood spots.

BACKGROUND: Dried blood filter cards, collected for newborn screening, are often stored for long periods of time. They may be suitable for the retrospective diagnosis of inborn errors of metabolism, but no data are currently available on the long-term stability of amino acids and acylcarnitine species. METHODS: We analyzed amino acids and acylcarnitines by tandem mass spectrometry in 660 anonymous, randomly selected filter cards from 1989 through 2004. We assessed long-term stability of metabolites by linear regression and estimated annual decrease of concentration for each metabolite. RESULTS: Concentrations of free carnitine increased by 7.6% per year during the first 5 years of storage and decreased by 1.4% per year thereafter. Alanine, arginine, leucine, methionine, and phenylalanine decreased by 6.5%, 3.3%, 3.1%, 7.3%, and 5.7% per year, respectively. Acetylcarnitine, propionylcarnitine, citrulline, glycine, and ornithine decreased by 18.5%, 27.4%, 8.1%, 14.7%, and 16.3% per year during the first 5 years, respectively; thereafter the decline was more gradual. Tyrosine decreased by 1.7% per year during the first 5 years and 7.9% per year thereafter. We could not analyze medium- and long-chain acylcarnitine species because of low physiological concentrations. CONCLUSIONS: Estimation of the annual decrease of metabolites may allow for the retrospective diagnosis of inborn errors of metabolism in filter cards that have been stored for long periods of time.