Barbka Repic Lampret

Comparison of tandem mass spectrometry and amino acid analyzer for phenylalanine and tyrosine monitoring—Implications for clinical management of patients with hyperphenylalaninemia

OBJECTIVES Regular and accurate monitoring of blood phenylalanine (Phe) and tyrosine (Tyr) levels is prerequisite for a successful management of patients with hyperphenylalaninemia (HPA). We aimed to compare the tandem mass spectrometry (MS/MS) and the amino acid analyzer (AAA) as methods to measure blood Phe and Tyr levels and Phe/Tyr ratio. METHODS Venous blood samples were collected for the AAA analysis, using Pinnacle PCX (Pickering Laboratories), with HPLC Series 1200 (Agilent). Capillary blood was spotted directly on filter paper (Whatman 903) for the MS/MS analysis, using 3200 QTrap AB SCIEX and Perkin Elmer Series 200 HPLC system. The Bland-Altman test was used to compare agreement between the methods and Pearson correlation coefficient to assess the association between the methods. RESULTS 207 pairs of measurements were performed. The Phe levels (range 0-2500μM) obtained by the MS/MS were on average 26.1% (SD 13.9%) lower compared to those obtained by the AAA. The Tyr levels by the MS/MS were on average 15.5% (SD 20.6%) lower. The Phe/Tyr ratio by the MS/MS was on average 10.6% (SD 15.9%) lower. The Pearson correlation coefficients for Phe (range 0-2500μM), Tyr and the Phe/Tyr ratio were 0.984 (p<0.001), 0.841 (p<0.001) and 0.987 (p<0.001) respectively. CONCLUSIONS When monitoring blood Phe and Tyr levels in patients with HPA, clinicians need to be informed about the method used. Due to the considerable inter-assay variability, a single method is preferable for long-term follow-up of patients. When using MS/MS, on average 26% lower blood Phe levels were obtained as compared to the AAA. The guidelines and recommendations on HPA management should take into consideration the differences in laboratory methods.

Newborn screening in southeastern Europe

The aim of our study was to assess the current state of newborn screening (NBS) in the region of southeastern Europe, as an example of a developing region, focusing also on future plans. Responses were obtained from 11 countries. Phenylketonuria screening was not introduced in four of 11 countries, while congenital hypothyroidism screening was not introduced in three of them; extended NBS programs were non-existent. The primary challenges were identified. Implementation of NBS to developing countries worldwide should be considered as a priority.

Assessment of tetrahydrobiopterin (BH4)-responsiveness and spontaneous phenylalanine reduction in a phenylalanine hydroxylase deficiency population

A BH(4) loading test was performed in 36 patients from 34 unrelated families. The patients had 29 different genotypes, and previous data on only eight of them were found in the BIOPKU database. Thirteen patients were classified as classic PKU (35.1%), 14 as mild PKU (37.8%) and 9 as MHP (27.0%). Blood Phe levels were shown to reach a plateau after three full days of increased natural protein ingestion. Measuring the 24-hour blood Phe levels (T(-24), T(-16), T(0)) on the fourth day of increased protein ingestion before BH(4) administration showed that within 24h Phe on average increased by 2.4% in MHP patients, decreased by 2.7% in mild PKU patients and increased by 9.7% in classic PKU patients (NS for all comparisons); Phe only slightly decreased in responders by 0.2% but increased in non-responders by 7.8% (P>0.05). Altogether, 16 of 36 (44.4%) patients represented by 12 of 29 (41.4%) different genotypes were proven to be BH(4) responders, and four (10.8%) were slow-responders. Responders were 6/9 (66.7%) MHP patients, 10/14 (71.4%) mild PKU patients and 0/13 classic PKU patients. Twenty of the 29 (68.9%) genotypes harbored at least one mutation with a known PRA of 10% or more but only 11 (55%) of them were BH(4)-responsive. Spontaneous reduction of blood Phe levels within 24h on the fourth day of natural protein loading was observed only in mild PKU patients and was shown not to be an important part of the BH(4)-response. 73.3% of genotypes containing at least one allele with a PRA of at least 30% were found to be BH(4) responsive; a PRA of at least 15.5% was needed for the responder genotype in our population.

Newborn Screening in Slovenia.

Abstract Introduction. Newborn screening in whole Slovenia started in 1979 with screening for phenylketonuria (PKU). Congenital hypothyroidism (CH) was added into the programme in 1981. The aim of this study was to analyse the data of neonatal screening in Slovenia from 1993 to 2012 for PKU, and from 1991 to 2012 for CH. Methods. Blood samples were collected from the heels of newborns between the third and the fifth day after birth. Fluorometric method was used for screening for PKU, CH screening was done by dissociationenhanced lanthanide fluorescent immunoassay (DELFIA). Results. From 1993 to 2012, from 385,831 newborns 57 were identified with PKU. 184 newborns out of 427,396 screened from 1991 to 2012, were confirmed for CH. Incidences of PKU and CH in the periods stated are 1:6769 and 1:2323, respectively. Conclusions. Successful implementation of newborn screening for PKU and CH has helped in preventing serious disabilities of the affected children. Adding screening for new metabolic diseases in the future would be beneficial. Izvleček Uvod. Presejanje novorojencev v Sloveniji se je začelo leta 1979 s presejanjem za fenilketonurijo (PKU). Leta 1981 je bil v program presejanja dodan še kongenitalni hipotireoidizem (CH). Cilj te raziskave je analiza podatkov presejanja novorojencev v Sloveniji v obdobju med letoma 1993 in 2012 za PKU ter med letoma 1991 in 2012 za CH. Metode. Vzorci krvi so bili odvzeti petim novorojencem med tretjim in petim dnem življenja. Pri presejanju za PKU se uporablja fluorometrična metoda, presejanje za CH pa poteka z metodo DELFIA. Rezultati. Od leta 1993 do leta 2012 je bil presejalni test za PKU izveden pri 358.831 novorojencih. Pri 57 otrocih je bil PKU potrjen. Pri 427.396 novorojencih med letoma 1991 in 2012 je bil izveden presejalni test za CH. Pri 184 otrocih je bil CH potrjen. V navedenih obdobjih je bila incidenca PKU 1:6769 in incidenca CH 1:2323. Zaključki. Uspešna implementacija presejanja novorojencev za PKU in CH je imela pomembno vlogo pri preprečevanju resnih zapletov pri obolelih otrocih. Smiselno bi bilo v program presejanja vključiti nove metabolne bolezni.

A case report of short-chain acyl-CoA dehydrogenase deficiency (SCADD)

Background Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is a rare inherited mitochondrial fatty acid oxidation disorder associated with variations in the ACADS (Acyl-CoA dehydrogenase, C-2 to C-3 short chain) gene. SCADD has highly variable biochemical, genetic and clinical characteristics. Phenotypes vary from fatal metabolic decompensation to asymptomatic individuals. Subject and methods A Romani boy presented at 3 days after birth with hypoglycaemia, hypotonia and respiratory pauses with brief generalized seizures. Afterwards the failure to thrive and developmental delay were present. Organic acids analysis with gas chromatography-mass spectrometry (GS/MS) in urine and acylcarnitines analysis with liquid chromatography-tandem mass spectrometry (LC-MS/MS) in dried blood spot were measured. Deoxyribonucleic acid (DNA) was isolated from blood and polymerase chain reactions (PCRs) were performed for all exons. Sequence analysis of all exons and flanking intron sequences of ACADS gene was performed. Results Organic acids analysis revealed increased concentration of ethylmalonic acid. Acylcarnitines analysis showed increase of butyrylcarnitine, C4-carnitine. C4-carnitine was 3.5 times above the reference range (<0.68 µmol/L). Confirmation analysis for organic acids and acylcarnitine profile was performed on the second independent sample and showed the same pattern of increased metabolites. Sequence analysis revealed 3-bp deletion at position 310-312 in homozygous state (c.310_312delGAG). Mutation was previously described as pathogenic in heterozygous state, while it is in homozygous state in our patient. Conclusions In our case clinical features of a patient, biochemical parameters and genetic data were consistent and showed definitely SCAD deficiency.

Cathepsin C Gene 5′-Untranslated Region Mutation in Papillon-Lefèvre Syndrome

Background: Papillon-Lefèvre syndrome (PLS) is a rare autosomal recessive disorder characterized by palmoplantar keratoderma together with a severe form of generalized aggressive periodontitis and associated with mutations in cathepsin C gene (CTSC). Objective: To investigate the clinical and mutational characteristics of 6 PLS patients from 4 unrelated Slovenian families. Methods:CTSC mutational and functional analyses were performed. Results: In all patients, a novel homozygous substitution, c.-55C>A, in the CTSC 5′-untranslated region (UTR) was detected on genomic DNA level and confirmed by mRNA analysis, resulting in the almost complete loss of CTSC mRNA expression and CTSC activity. In silico analysis revealed the potential of the mutation to disrupt putative transcription factor binding sites (TFBSs) for AP-2 and Sp families of transcription factors. Conclusion: Identification of a novel CTSC 5′-UTR mutation together with a severe reduction of CTSC mRNA expression and virtually nonexistent CTSC activity was suggestive of a novel mechanism of TFBS dysfunction associated with PLS.

Long-term BH4 (sapropterin) treatment of children with hyperphenylalaninemia - effect on median Phe/Tyr ratios.

Abstract Background: Phenylalanine hydroxylase deficiency causes various degrees of hyperphenylalaninemia (HPA). Tetrahydrobiopterin (BH4; sapropterin) reduces phenylalanine (Phe) levels in responders, enabling relaxation of dietary therapy. We aimed to assess long-term effects of BH4 treatment in HPA patients. Methods: Nine pre-pubertal BH4 responsive children were treated with BH4 for at least 2 years. The median dietary tolerance to Phe and levels of blood Phe, tyrosine (Tyr), zinc, selenium and vitamin B12 and anthropometric measurements, in the 2 years periods before and after the introduction of BH4 treatment were analyzed and compared. Adverse effects of BH4 were assessed. Results: The daily Phe tolerance had tripled, from pretreatment median value of 620 mg (IQR 400–700 mg) to 2000 (IQR 1000–2000 mg) after 2 years of follow up (p<0.001). The median blood Phe levels during the 2 years period before introducing BH4 did not change significantly during the 2 years on therapy (from 200 μmol/L; IQR 191–302 to 190 μmol/L; IQR 135–285 μmol/L), but the median blood Phe/Tyr ratio had lowered significantly from pre-treatment value 4.7 to 2.4 during the 2 years on therapy (p=0.01). Median zinc, selenium, vitamin B12 levels and anthropometric measurements did not change while on BH4 therapy (p=NS). No adverse effects were noticed. Conclusions: BH4 therapy enabled patients much higher dietary Phe intakes, with no noticeable adverse effects. Median blood Phe and Tyr levels, median zinc, selenium, vitamin B12 levels and anthropometric measurements did not change significantly on BH4 therapy, but median Phe/Tyr ratios had lowered.

Next generation sequencing as a follow-up test in an expanded newborn screening programme.

OBJECTIVES Contrary to many western European countries, most south-eastern European countries do not have an expanded newborn screening (NBS) program using tandem mass spectrometry. This study would represent one of the first expanded NBS studies in south-eastern Europe and will enable the estimation of the incidences of IEM in Slovenia. We proposed an expanded NBS approach including next-generation sequencing (NGS) as a confirmational analysis. DESIGN & METHODS We conducted a pilot study of expanded NBS for selected inborn errors of metabolism (IEM) in Slovenia including 10,048 NBS cards. We used an approach including tandem mass spectrometry followed by second tier tests including NGS. Based on the NBS results, 85 children were evaluated at a metabolic follow-up; 80 of them were analyzed using NGS. RESULTS Altogether, glutaric acidemia type 1 was confirmed in one patient who was a compound heterozygote for two known causative GCDH variants. A patient with suspected very long-chain acyl-CoA dehydrogenase deficiency had negative metabolic follow-up tests, but had two heterozygous ACADVL variants; one known disease-causing variant and one indel, namely c.205-8_205-7delinsGC, that is predicted to be causative. Nine participants had elevated metabolites characteristic of 3-methylcrotonyl-CoA carboxylase deficiency, 2 of them had known causative homozygous variants in MCCC1. The other seven were heterozygous; two had a novel genetic variant c.149_151dupCCA (p.Thr50dup). Cumulative incidences of IEM in Slovenia were similar to other European countries. CONCLUSIONS NGS proved to be valuable in explaining the abnormal metabolite concentrations in NBS as it enabled the differentiation between affected patients and mere heterozygotes, and it improved the turnaround time of genetic analysis. The results of this study will be instrumental in the routine implementation of expanded NBS in Slovenia.

Selective Screening for Metabolic Disorders in the Slovenian Pediatric Population/Selektivni Skrining Metaboličkih Poremećaja Kod Dečije Populacije U Sloveniji

Summary Background: Inborn errors of metabolism (IEM) are disorders with a block in the metabolic pathway caused by a genetic defect of a specific enzyme. Although each of these diseases is quite rare, as a group they account for a significant proportion of newborn and childhood morbidity and mortality. Early diagnosis is important to prevent complications or even death of the child. Selective screening is an important diagnostic tool for the diagnosis of IEM. Methods: In Slovenia, symptomatic patients with suspected IEM are referred to the University Children’s Hospital Ljubljana. Techniques used for selective screening are gas chromatography-mass spectrometry, ion exchange chromatography-post-column derivatization, liquid chromatography-tandem mass spectrometry and isoelectric focusing. Fluorimetric method is used for enzyme activity measurement. Results: There are 168 patients with amino and organic acidemias, 5 patients with disorders in fatty acids metabolism, 1 patient with a congenital disorder of glycosylation, 42 patients with Fabry disease (of which 37 are adult) and 20 patients with Gaucher disease (of which 18 are adult) in the Slovenian Register for Rare Diseases. Conclusions: In Slovenia, management of patients with IEM is centralized at the University Children’s Hospital, with the exception of adult patients with Fabry and Gaucher disease. The team work is well organized with close cooperation between the laboratory and pediatricians specialized in metabolic disorders. According to the known frequencies of IEM from the literature, we would expect more positive results than obtained. To evaluate these results, we are planning to perform a pilot study on expanded newborn screening. Kratak sadržaj Uvod: Uro|eni poremećaji metabolizma (inborn errors of metabolism, IEM) jesu bolesti kod kojih postoji blokada u metabolićkom putu prouzrokovana nedostatkom specifićnog enzima. Mada se pojedinaćno sve ove bolesti prilićno retko javljaju, u celosti one znaćajno doprinose mortalitetu i morbiditetu novoro|enćadi i dece. Pravovremena dijagnoza je zato od izuzetnog znaćaja za sprećavanje komplikacija ili ćak smrti dece. Selektivni skrining je važna dijagnostićka alatka za dijagnozu IEM. Metode: Pacijenti kod kojih postoji sumnja na IEM upućeni su u Univerzitetsku dećiju bolnicu u Ljubljani. Za selektivni skrining upotrebljavamo sledeće tehnike: gasnu masenu spektrometriju, jonskoizmenjivaćku postkolonsku derivatizaciju, tećnu hromatografijutandemsku masenu spektrometriju i izoelektrićno fokusiranje. Aktivnost enzima merimo fluorimetrijskom metodom. Rezultati: U Registru retkih bolesti Slovenije zabeleženo je 168 pacijenata sa amino i organskim acidemijama, 5 pacijenata s poremećajem u metabolizmu masnih kiselina, 1 pacijent s kongenitalnim poremećajem glikozilacije, 42 pacijenta s Fabrijevom bolešću (37 su odrasli pacijenti) i 20 pacijenata s Gaucherovom bolešću (37 su odrasli pacijenti). Zakljućak: Medicinska pomoć za pacijente sa IEM centralizovana je na jednom mestu, u Univerzitetskoj dećijoj bolnici, osim odraslih pacijenata s Fabrijevom i Gaucherovom bolešću. Radi se o dobro organizovanom timskom radu, sa tesnom saradnjom izme|u laboratorije i specijaliste za metabolizam. S obzirom na ućestalost pojavljivanja IEM poznatu iz literature, oćekivali smo više pozitivnih rezultata nego što ih dobijamo. Za procenu naših rezultata planiramo izvo|enje pilotske studije sa proširenim skriningom novoro|enćadi.

Medium-chain acyl-CoA dehydrogenase deficiency: Two novel ACADM mutations identified in a retrospective screening:

Objective The aim of this study was to determine whether an expanded newborn screening programme, which is not yet available in Slovenia, would have detected the first two patients with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency in the country. Two novel ACADM mutations are also described. Methods Both patients were diagnosed clinically; follow-up involved analysis of organic acids in urine, acylcarnitines in dried blood spots, and genetic analysis of ACADM. Cut-off values of acylcarnitines in newborns were established using analysis of 10,000 newborns in a pilot screening study. Results In both patients, analysis of the organic acids in urine showed a possible β-oxidation defect, while the specific elevation of acylcarnitines confirmed MCAD deficiency. Subsequent genetic analysis confirmed the diagnosis; both patients were compound heterozygotes, each with one novel mutation (c.861 + 2T > C and c.527_533del). The results from a retrospective analysis of newborn screening cards clearly showed major elevations of MCAD-specific acylcarnitines in the patients. Conclusions An expanded newborn screening programme would be beneficial because it would have detected MCAD deficiency in both patients before the development of clinical signs. Our study also provides one of the first descriptions of ACADM mutations in Southeast Europe.