Data on phenylalanine-to-tyrosine ratios in assessment of tetrahydrobiopterin (BH4)-responsiveness in patients with hyperphenylalaninemia.

Blood phenylalanine-to-tyrosine (Phe/Tyr) ratio is an important indicator of metabolic control in phenylketonuria patients. We present the data that highlights the role of Phe/Tyr-ratio in the evaluation of tetrahydrobiopterin (BH4)-responsiveness in patients with hyperphenylalaninemia. Our data complements the results from the original research article by Tansek et al., 2012 [1]. We performed a BH4-loading test in 32 patients after four days of increased protein intake (2000 mg/kg body weight). Blood sampling was performed 96, 72, 48, 24, 16 h, and moments before oral administration of BH4 in a dose of 20 mg/kg body weight. Additional blood samples were collected 8 and 24 h after its administration. Phenylalanine (Phe) and Tyrosine (Tyr) levels were determined from dried blood spots by tandem mass spectrometry. Phe/Tyr-ratio reached a plateau after three days of increased dietary protein intake. Fifteen patients (47%) responded to BH4, defined as a decrease of Phe-of at least 30% after 24 h of BH4 administration. Phe/Tyr-ratios were significantly higher in non-responders compared to responders. In the responder group, Phe/Tyr-ratios decreased in average of 67% (p = 0.001) and 45% (p = 0.001) after 8 and 24 h of BH4 administration, respectively. Phe/Tyr-ratio decreased after 8 h of drug administration also in the non-responder group, but not 24 h after administration.

Expanded Newborn Screening Program in Slovenia using Tandem Mass Spectrometry and Confirmatory Next Generation Sequencing Genetic Testing.

INTRODUCTION: In the last two decades, the introduction of tandem mass spectrometry in clinical laboratories has enabled simultaneous testing of numerous acylcarnitines and amino acids from dried blood spots for detecting many aminoacidopathies, organic acidurias and fatty acid oxidation disorders. The expanded newborn screening was introduced in Slovenia in September 2018. Seventeen metabolic diseases have been added to the pre-existing screening panel for congenital hypothyroidism and phenylketonuria, and the newborn screening program was substantially reorganized and upgraded. METHODS: Tandem mass spectrometry was used for the screening of dried blood spot samples. Next-generation sequencing was introduced for confirmatory testing. Existing heterogeneous hospital information systems were connected to the same laboratory information system to allow barcode identification of samples, creating reports, and providing information necessary for interpreting the results. RESULTS: In t he first y ear of t he expanded newborn screening a total of 15,064 samples w ere screened. Four patients were confirmed positive with additional testing. CONCLUSIONS: An expanded newborn screening program was successfully implemented with the first patients diagnosed before severe clinical consequences.

A patient with glycogen storage disease type 0 and a novel sequence variant in GYS2: a case report and literature review.

Glycogen storage disease type 0 (GSD0) is an autosomal recessive disorder caused by a sequence variant in the GYS2 gene, leading to decreased or absent activity of hepatic glycogen synthase. With a frequency of less than 1 in 1,000,000 individuals, GSD0 represents only around 1% of all glycogen storage disease cases but it might be underrecognized. A 13-month-old girl of reportedly unrelated parents presented with a decreased level of consciousness, twitching in her left cheek, and munching. During a fasting test, hyperketotic hypoglycemia was found. A novel homozygous GYS2 gene sequence variant p.Thr445Arg was later confirmed by next-generation gene sequencing. After establishing a cornstarch- and protein-rich diet, the hypoglycemic episodes subsided and the patient's neurocognitive development was normal. To date, only 39 patients with 24 disease-causing gene variants have been identified in GSD0, and we review their characteristics. Because of the heterogeneous phenotypes, GSD0 is an underdiagnosed disorder. In patients with hyperketotic hypoglycemia and postprandial hyperglycemia, GYS2 gene analysis should be performed.

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

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.

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.

Selective Screening for Metabolic Disorders in the Slovenian Pediatric Population.

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.

Fifty years of phenylketonuria newborn screening - A great success for many, but what about the rest?

Guthrie's landmark discovery and the subsequent implementation of the first newborn screening programs for phenylketonuria (PKU) and other inherited errors of metabolism (IEM) could be - in a 50 year retrospective - easily considered among the greatest advances in medicine. They have not just improved the quality of hundreds of thousands of lives, but also transformed our understanding and approach to PKU and IEM in general. However, according to the available albeit very scarce data, many countries and regions seem not to share the benefits of the last 50 years of development. Many of them have not yet introduced the newborn screening for PKU or face significant problems in its implementation. In addition, the issue seems to be underrated by the relevant professional forums. Action to improve the current situation should urgently be taken.

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 (BH(4))-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.

Five novel mutations and two large deletions in a population analysis of the phenylalanine hydroxylase gene.

Mutational spectrum of the phenylalanine hydroxylase (PAH) deficiency was investigated in 107 families (90% of the Slovene PKU population). The entire coding region of the PAH gene was analyzed with dHPLC to select the samples where subsequently the automated sequencing analysis was performed. MLPA analysis was performed to identify large deletions, which were later confirmed with long-range PCR. Correlations with patients' phenotypes and genotype-based predictions of BH(4)-responsiveness were assessed. Altogether, disease-causing mutations were identified on 209 alleles (detection rate 97.7%). A spectrum of 36 different disease-causing mutations was identified: 20 missense mutations (80% of the alleles), eight splicing mutations (13% of the alleles), one nonsense mutation (0.5% of the alleles), four small deletions with frame shift (6% of the alleles), one small insertion with frame shift (0.5% of the alleles), and two large deletions (2% of the alleles). The most frequent mutation was p.R408W in exon 12, representing 29% of the alleles, which is in concordance with other neighboring and/or Slavic PKU populations. Other common mutations were: p.R158Q, p.A403V, p.P281L and p.E390G, accounting for 9%, 7%, 7% and 7% of the alleles respectively. Five novel mutations were detected: c.43_44insAG, c.56_59+1delACAGG, p.V45A, p.L62P and p.R157S. Large deletion of exon 5 (EX5del955) was found in three patients and a deletion of exon 3 (EX3del4765) in one patient. A spectrum of 64 different genotypes was found, seven of them accounting for over than a third of all families. Among thirteen families with homozygous mutation (13% of the PKU population), 10 had p.R408W, two had p.R158Q and one had p.E390G. Among 107 families, 58 were classified as classic PKU (54.2%), 28 as mild PKU (25.9%) and 21 as MHP (19.6%). Twenty-six different genotypes (40.6%) were predicted to be BH(4)-responsive, represented by 38 different families (35.5%).

Management of neonatal and infancy-onset diabetes mellitus.

Diabetes mellitus is a rare disorder during the first 2 years of life, amounting to about 3-5% of all cases diagnosed before the fifteenth birthday. However, in spite of low numerical values, this is an important diagnosis, since we are dealing with a vulnerable age group with major and special problems related to diagnosis, treatment and psychosocial follow-up. Efforts should be made to establish a molecular genetic diagnosis as early as possible (e.g. homozygous glucokinase deficiency, defects of the ATP-sensitive potassium channel, chromosome 6 imprinting abnormalities). This is particularly important, since patients with Kir6.2 and SUR1 defects can now be treated with oral sulfonylureas. Major advancements have been obtained and continue to be made with respect to diagnosis and classification. Differentiation between transient and permanent neonatal diabetes can only be done after long-term follow-up. Patients should be scrutinized for comorbidity (e.g. celiac disease, Wolcott-Rallison syndrome). Type 1 diabetes is probably the most prevalent subtype, particularly after the first year of life. Insulin treatment in infancy continues to represent major technical, medical and psychological challenges. Family support is mandatory and close attention should be paid to psychosocial issues.

Obesity due to proopiomelanocortin deficiency: three new cases and treatment trials with thyroid hormone and ACTH4-10.

The symptoms of severe early-onset obesity, adrenal insufficiency, and red hair define the proopiomelanocortin (POMC) deficiency syndrome as described so far in two children with complete loss-of-function mutations of the human POMC gene. In POMC deficiency, obesity reflects the lack of POMC-derived peptides as ligands at the melanocortin (MC) MC4 and MC3 receptors, which are expressed in the hypothalamic leptin-melanocortin pathway of body weight regulation. Hypocortisolism and alteration of pigmentation are caused by the lack of POMC-derived peptides at the adrenal MC2 receptor and the skin MC1 receptor, respectively. Here we describe three new cases of complete loss-of-function mutations of the POMC gene. Patients were diagnosed based on the clinical trials of red hair, adrenal insufficiency, and early-onset severe obesity. One previously described translation initiation mutation (C3804A) as well as one new nonsense (A6851T) and two new frame-shift mutations (6996del and 7100 + 2G) were found in homozygosity or compound heterozygosity. The heterozygous parents were found to have high normal or mildly elevated body weight, suggesting a dosage effect of the POMC gene product on weight regulation. To compensate for the lack of hypothalamic melanocortin function, we initiated a trial in the two previously published patients with intranasal ACTH4-10, a melanocortin fragment for which an anorexic effect has been described recently. During 3 months with increasing doses of ACTH4-10, no change of body weight or metabolic rate was observed, suggesting that at least in these two POMC-deficient patients ACTH4-10 is without any compensatory effect. In the same two patients, further investigation revealed a mildly elevated TSH. However, a 1-yr treatment with thyroid hormone did not result in a significant reduction of body weight.