Epidemiology and natural history of POLG disease in Norway: a nationwide cohort study.

OBJECTIVE: To investigate the prevalence and natural history of POLG disease in the Norwegian population. METHODS: A national, population-based, retrospective study using demographic, clinical, and genetic data of patients with genetically confirmed POLG disease. The patients were diagnosed between 2002 and 2022, and were included into the Norwegian POLG Patient Registry. Patients were stratified according to age at disease onset (early <12 years, juvenile to adult 12-40 years, late ≥40 years) and resident region. RESULTS: Ninety-one patients were included. The point prevalence of POLG disease was 1:149,253. Birth prevalence was 1:48,780. Median age at clinical onset was 16 years (range: 2 months to 70 years). Onset occurred early in 35% (32 out of 91), juvenile-adult in 55% (50 out of 91) and late in 10% (9 out of 91). A distinct seasonal pattern in disease onset was observed, with 57% (52 out of 91) presenting between May and August. Forty-five patients (49%) had acute exacerbations that required intensive care, and this affected 72% of those in the early-onset group. The mortality rate was 54% (49 out of 91), with a median time from disease onset to death of 3 years (range: 1 month to 36 years). INTERPRETATION: We provide the point prevalence and birth prevalence of POLG disease in the first nationwide study in which epidemiological and clinical data were integrated. Seasonal variations in clinical onset may offer valuable insights into disease mechanisms and modifying factors. The findings from this study are crucial for quantifying the disease burden, and contribute to evidence-based healthcare planning.

Fasting and non-fasting plasma levels of monomethyl branched chain fatty acids: Implications for maple syrup urine disease.

The branched-chain amino acids (BCAA) leucine, valine, and isoleucine provide precursors for monomethyl branched-chain fatty acids (BCFA). Established reference ranges for BCFAs are lacking. In maple syrup urine disease (MSUD), a rare inborn error of BCAA metabolism, the endogen production is impaired and MSUD patients are treated with a low protein (low BCAA) diet. The protein restriction may affect the dietary intake of BCFA, depending on the dietary choices made. Patients with MSUD are prescribed a more or less protein-restricted diet depending on the severity of the disease. The combination of a protein-restricted diet and subsequent impaired endogenous synthesis may render MSUD patients sensitive to BCFA deficiency, with yet unknown implications. To investigate the possibility of lower circulatory BCFA levels in MSUD that favors dietary BCFA supplementation, we first established fasting-state reference ranges for selected BCFAs and saturated/unsaturated fatty acids in plasma. Then, the effect of fasting on BCFA levels was evaluated by comparing the distribution in a fasting versus a non-fasting cohort. To test the hypothesis that BCFA deficiency could contribute to MSUD pathophysiology, we recruited patients with intermittent, intermediate, and classical form of MSUD and analyzed the corresponding BCFA z-scores. None of the BCFA species had |z-scores| > 2 relative to the reference range. Our findings do not support the requirement of BCFA supplementation in MSUD patients. The origin of BCFAs is discussed. Impaired capacity to synthesize BCFA do not manifest as reduced plasma levels in MSUD, suggesting that endogenous synthesis is dispensable for plasma levels.

Case report: ADHD and prognosis in tyrosinemia type 1.

Neurometabolic disorders such as tyrosinemia type 1 (TYRSN1) may interfere with brain metabolism and show symptoms of attention-deficit hyperactivity disorder (ADHD) in patients treated with the enzyme inhibitor nitisinone [2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione, NTBC]. It has been reported that ADHD treatment improves treatment compliance, which is imperative for the long-term prognosis of patients with TYRSN1. In this study, we report the case of a male patient who was diagnosed with TYRSN1 at 3 months of age and was subsequently treated with NTBC, restricted protein intake, and amino acids supplementation. At 7 years of age, he was referred for neuropsychiatric assessment, diagnosed with ADHD, and treated with methylphenidate. The effects of the treatment were monitored via parental interviews, questionnaires covering ADHD symptoms, and a continuous performance test. A reduction in ADHD symptoms, particularly inattentiveness, was observed across all measures. The early identification of ADHD and the treatment of neurometabolic disorders, such as TYRSN1, may be important from a lifetime perspective as this may improve the prognosis of the medical condition as well.

Renal function, sex and age influence purines and pyrimidines in urine and could lead to diagnostic misinterpretation.

Glomerular filtration rate (GFR) is commonly used in clinical practice for the diagnosis and follow-up of chronic kidney disease. Screening for inborn errors of metabolism (IEM) is based on analysis of biomarkers in urine, reported by their ratio to urinary creatinine (crn). Impaired renal function may complicate the interpretation of several biomarkers used for screening of IEM. Our goal was to investigate the influence of kidney function, in terms of measured GFR (mGFR) on purines and pyrimidines in urine, in addition to the relationship to sex, age, pH and ketosis. Children (n = 96) with chronic kidney disease (CKD), in different CKD stages, were included. Urine samples were obtained prior to the injection of iohexol. Serum samples at 7 time-points were used to calculate mGFR based on iohexol plasma clearance. The association with sex, age, ketosis and pH was examined in samples of the laboratory production from 2015 to 2021 (n = 8192). Age was a highly significant covariate for all markers. GFR correlated positively to several purines and pyrimidines; the ratios hypoxanthine/crn, xanthine/crn and urate/crn (p = 2.0 × 10-14, < 3 × 10-15 and 7.2 × 10-4, respectively), and the ratios orotic acid/crn, uracil/crn, and carbamyl-ß-alanine/crn (p = 0.03, 1.4 × 10-6 and 0.003, respectively). The values of urate/crn, xanthine/crn, uracil/crn, and carbamyl-ß-alanine/crn were higher in females above 16 years of age. Ketosis and pH influenced some markers. In conclusion, decreased renal function interferes with the excretion of urinary purines and pyrimidines, and this could change decision limits substantially, e.g. result in false negative results in Lesch-Nyhan syndrome. SYNOPSIS: GFR influences purines and pyrimidines in urine. Clinical Trial Registration: ClinicalTrials.gov, Identifier NCT01092260, https://clinicaltrials.gov/ct2/show/NCT01092260?term=tondel&rank=2.

Novel mutations in the HADHB gene causing a mild phenotype of mitochondrial trifunctional protein (MTP) deficiency.

Mitochondrial trifunctional protein (MTP) deficiency is an ultrarare hereditary recessive disorder causing a broad spectrum of phenotypes with lethal infantile cardiomyopathy at the most severe end. Attenuated forms with polyneuropathy have been reported combined with myoglobinuria or rhabdomyolysis as key features. We here report three young adults (two siblings) in which three variants in the HADHB-gene were identified. All three cases had a similar mild phenotype with axonal neuropathy and frequent intermittent weakness episodes but without myoglobinuria. Special dietary precautions were recommended to minimize complications especially during infections and other catabolic states. MTP deficiency is therefore an important differential diagnosis in patients with milder fluctuating neuromuscular symptoms. Take­home message: Axonal neuropathy and recurrent muscular weakness without concomitant rhabdomyolysis may be due to MTP deficiency.

A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.

COX16 is involved in the biogenesis of cytochrome-c-oxidase (complex IV), the terminal complex of the mitochondrial respiratory chain. We present the first report of two unrelated patients with the homozygous nonsense variant c.244C>T(p. Arg82*) in COX16 with hypertrophic cardiomyopathy, encephalopathy and severe fatal lactic acidosis, and isolated complex IV deficiency. The absence of COX16 protein expression leads to a complete loss of the holo-complex IV, as detected by Western blot in patient fibroblasts. Lentiviral transduction of patient fibroblasts with wild-type COX16 complementary DNA rescued complex IV biosynthesis. We hypothesize that COX16 could play a role in the copper delivery route of the COX2 module as part of the complex IV assembly. Our data provide clear evidence for the pathogenicity of the COX16 variant as a cause for the observed clinical features and the isolated complex IV deficiency in these two patients and that COX16 deficiency is a cause for mitochondrial disease.

Performance of Expanded Newborn Screening in Norway Supported by Post-Analytical Bioinformatics Tools and Rapid Second-Tier DNA Analyses.

In 2012, the Norwegian newborn screening program (NBS) was expanded (eNBS) from screening for two diseases to that for 23 diseases (20 inborn errors of metabolism, IEMs) and again in 2018, to include a total of 25 conditions (21 IEMs). Between 1 March 2012 and 29 February 2020, 461,369 newborns were screened for 20 IEMs in addition to phenylketonuria (PKU). Excluding PKU, there were 75 true-positive (TP) (1:6151) and 107 (1:4311) false-positive IEM cases. Twenty-one percent of the TP cases were symptomatic at the time of the NBS results, but in two-thirds, the screening result directed the exact diagnosis. Eighty-two percent of the TP cases had good health outcomes, evaluated in 2020. The yearly positive predictive value was increased from 26% to 54% by the use of the Region 4 Stork post-analytical interpretive tool (R4S)/Collaborative Laboratory Integrated Reports 2.0 (CLIR), second-tier biochemical testing and genetic confirmation using DNA extracted from the original dried blood spots. The incidence of IEMs increased by 46% after eNBS was introduced, predominantly due to the finding of attenuated phenotypes. The next step is defining which newborns would truly benefit from screening at the milder end of the disease spectrum. This will require coordinated international collaboration, including proper case definitions and outcome studies.

Tyrosinemia Type 1 and symptoms of ADHD: Biochemical mechanisms and implications for treatment and prognosis.

Hereditary tyrosinemia Type 1 (HT-1) is a rare metabolic disease where the enzyme catalyzing the final step of tyrosine breakdown is defect, leading to accumulation of toxic metabolites. Nitisinone inhibits the degradation of tyrosine and thereby the production of harmful metabolites, however, the concentration of tyrosine also increases. We investigated the relationship between plasma tyrosine concentrations and cognitive functions and how tyrosine levels affected enzyme activities of human tyrosine hydroxylase (TH) and tryptophan hydroxylase 2 (TPH2). Eight Norwegian children between 6 and 18 years with HT-1 were assessed using questionnaires measuring Attention Deficit Hyperactivity Disorder (ADHD)-symptoms and executive functioning. Recent and past levels of tyrosine were measured and the enzyme activities of TH and TPH2 were studied at conditions replicating normal and pathological tyrosine concentrations. We observed a significant positive correlation between mean tyrosine levels and inattention symptoms. While TH exhibited prominent substrate inhibition kinetics, TPH2 activity also decreased at elevated tyrosine levels. Inhibition of both enzymes may impair syntheses of dopamine, noradrenaline, and serotonin in brain tissue. Inattention in treated HT-1 patients may be related to decreased production of these monoamines. Our results support recommendations of strict guidelines on plasma tyrosine levels in HT-1. ADHD-related deficits, particularly inattention, should be monitored in HT-1 patients to determine whether intervention is necessary.

Pyruvate dehydrogenase deficiency. / Pyruvatdehydrogenase-mangel.

Pyruvate dehydrogenase deficiency is a rare mitochondrial disease leading to energy deficiency in the cells. This particularly affects the central nervous system, resulting in a broad range of neurological symptoms.

An intronic variation in SLC52A1 causes exon skipping and transient riboflavin-responsive multiple acyl-CoA dehydrogenation deficiency.

Vitamin B2, riboflavin is essential for cellular function, as it participates in a diversity of redox reactions central to human metabolism, through its role as precursor for the cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are electron carriers. The electron transfer flavoprotein (ETF) and its dehydrogenase (ETFDH), uses FAD as cofactor. The ETF and ETFDH are forming the electron transport pathway for many mitochondrial flavoprotein dehydrogenases involved in fatty acid, amino acid and choline metabolism. A variation in either ETF or ETFDH causes multiple acyl-CoA dehydrogenation deficiency (MADD), but genetic variations in the riboflavin metabolism or transportation of riboflavin can also cause MADD. The most common variations are located in the riboflavin transporter 2 (RFVT2) and 3 (RFVT3), that are highly expressed in brain and intestinal tissues, respectively. Deficiency of riboflavin transporter 1 (RFVT1), encoded by the SLC52A1 gene, highly expressed in the placenta, has only been reported once. We here report a case of transient MADD, caused by a heterozygous intronic variation, c.1134+11G>A, in the SLC52A1 gene encoding RFVT1. This variation creates a binding site for the splice inhibitory hnRNP A1 protein and causes exon 4 skipping. Riboflavin deficiency and maternal malnutrition during pregnancy might have been the determining factor in the outcome of this case.

A novel mutation in FBXL4 in a Norwegian child with encephalomyopathic mitochondrial DNA depletion syndrome 13.

Mitochondrial DNA depletion syndromes (MTDPS) represent a clinically and genetically heterogeneous group of autosomal recessive disorders, caused by mutations in genes involved in maintenance of mitochondrial DNA (mtDNA). Biallelic mutations in FBXL4 were recently described to cause encephalomyopathic MTDPS13. The syndrome has infantile onset and presents with hypotonia, feeding difficulties, a pattern of mild facial dysmorphisms, global developmental delay and brain atrophy. Laboratory investigations reveal elevated blood lactate levels, unspecific mitochondrial respiratory chain (MRC) enzyme deficiencies and mtDNA depletion. We report a novel missense variant, c.1442T > C (p.Leu481Pro), in FBXL4 (NM_012160.4) in a Norwegian boy with clinical, biochemical and cerebral MRI characteristics consistent with MTDPS13. The FBXL4 c.1442T > C (p.Leu481Pro) variant was not present in public databases, 149 Norwegian controls nor an in-house database containing whole exome sequencing data from 440 individuals, and it was predicted in silico to be deleterious to the protein function. Activities of MRC enzymes were normal in muscle tissue (complexes I-IV) and cultured skin fibroblasts (complexes I-V) from the patient, but mtDNA depletion was confirmed in muscle, thus supporting the predicted pathogenicity of the FBXL4 c.1442T > C (p.Leu481Pro) variant. On clinical indication of mitochondrial encephalomyopathy, sequencing of FBXL4 should be performed, even when the activity levels of the MRC enzymes are normal.

Cross-sectional study of 168 patients with hepatorenal tyrosinaemia and implications for clinical practice.

BACKGROUND: Hepatorenal tyrosinaemia (Tyr 1) is a rare inborn error of tyrosine metabolism. Without treatment, patients are at high risk of developing acute liver failure, renal dysfunction and in the long run hepatocellular carcinoma. The aim of our study was to collect cross-sectional data. METHODS: Via questionnaires we collected retrospective data of 168 patients with Tyr 1 from 21 centres (Europe, Turkey and Israel) about diagnosis, treatment, monitoring and outcome. In a subsequent consensus workshop, we discussed data and clinical implications. RESULTS: Early treatment by NTBC accompanied by diet is essential to prevent serious complications such as liver failure, hepatocellular carcinoma and renal disease. As patients may remain initially asymptomatic or develop uncharacteristic clinical symptoms in the first months of life newborn mass screening using succinylacetone (SA) as a screening parameter in dried blood is mandatory for early diagnosis. NTBC-treatment has to be combined with natural protein restriction supplemented with essential amino acids. NTBC dosage should be reduced to the minimal dose allowing metabolic control, once daily dosing may be an option in older children and adults in order to increase compliance. Metabolic control is judged by SA (below detection limit) in dried blood or urine, plasma tyrosine (<400 µM) and NTBC-levels in the therapeutic range (20-40 µM). Side effects of NTBC are mild and often transient. Indications for liver transplantation are hepatocellular carcinoma or failure to respond to NTBC. Follow-up procedures should include liver and kidney function tests, tumor markers and imaging, ophthalmological examination, blood count, psychomotor and intelligence testing as well as therapeutic monitoring (SA, tyrosine, NTBC in blood). CONCLUSION: Based on the data from 21 centres treating 168 patients we were able to characterize current practice and clinical experience in Tyr 1. This information could form the basis for clinical practice recommendations, however further prospective data are required to underpin some of the recommendations.

High dietary folic Acid and high plasma folate in children and adults with phenylketonuria.

BACKGROUND: PKU patients on a strict low protein diet get most of their folic acid intake from protein substitute. Several protein substitutes contain high amounts of this vitamin. Concern has been raised about the safety of high levels of folic acid, especially in relation to cancer risk. METHODS: This cross-sectional study included 34 children and 22 adults with PKU. A dietary interview was performed and intake of folic acid and vitamin B12 from protein substitute was calculated for patients compliant with their protein substitute. Intakes of folic acid and vitamin B12 were compared with plasma levels of folate, vitamin B12, and homocysteine. RESULTS: Children aged 2-9 years had the highest intake of folic acid according to RDI (449 %), and children aged 7-10 years had the highest intake of folic acid according to UL (155 %). Median plasma folate level in PKU children was two times the upper reference level and in PKU adults well above. Children between 10 and 13 years had the highest level of plasma folate. Young children had both a high intake and high plasma levels of vitamin B12. Homocysteine levels were low or in the lower part of the normal reference range in most patients. CONCLUSION: Children with PKU are at a particular risk of receiving folic acid high above RDI and many children with PKU receive doses above the UL. Many PKU patients have a very high level of plasma folate related to a very high content of folic acid in many of their protein substitutes.

Fumarylacetoacetate inhibits the initial step of the base excision repair pathway: implication for the pathogenesis of tyrosinemia type I.

Hereditary tyrosinemia type I (HT1) is an autosomal recessive disease caused by a deficiency in human fumarylacetoacetate (FAA) hydrolase (FAH), which is the last enzyme in the catabolic pathway of tyrosine. Several reports suggest that intracellular accumulation of intermediates of tyrosine catabolism, such as FAA and succinylacetone (SA) is important for the pathogenesis in liver and kidney of HT1 patients. In this work, we examined the effect of FAA and SA on DNA glycosylases initiating base excision repair (BER), which is the most important pathway for removing mutagenic DNA base lesions. In vitro assays monitoring DNA glycosylase activities demonstrated that FAA but not SA inhibited base removal. In particular, the Neil1 and Neil2 DNA glycosylases were strongly inhibited, whereas inhibition of Nth1 and Ogg1 were less efficient. These DNA glycosylases initiate excision of a broad range of mutagenic oxidative base lesions. Further, FAA showed a modest inhibitory effect on the activity of the alkylbase DNA glycosylase Aag and no significant inhibition of the uracil DNA glycosylase Ung2. These data indicate that FAA inhibition of DNA glycosylases removing oxidative base lesions in HT1 patients may increase mutagenesis, suggesting an important mechanism for development of hepatocarcinoma and somatic mosaicism.

Hereditary tyrosinaemia type I in Norway: incidence and three novel small deletions in the fumarylacetoacetase gene.

A total of 28 Norwegians have been diagnosed with hereditary tyrosinaemia type I (HT1) over the last 30 years. In this study, 19 of these patients were investigated. Three novel small deletions were found (NM_000137.1(FAH): c.615delT, p.Phe205LeufsX2, NM_000137.1(FAH): c.744delG, p.Pro249HisfsX55 and NM_000137.1(FAH):c835delC) pGln279ArgfsX25, all of them leading to a change in the reading frame and a premature stop codon. We hereby genetically characterized 51 of the 56 disease-causing alleles, identifying nine different disease-causing mutations in the Norwegian population. We found that 65% of the Norwegian HT1 patients are compound heterozygous for different mutations. Thus, the relatively high incidence of HT1 in Norway of 1 in 74,800 live births is not due to single founder effects or high incidence of parental consanguinity.

Validation of the Hemo_Control instrument for determination of B-haemoglobin concentration in primary health care.

OBJECTIVE: The aim of this study was to evaluate the analytical performance of a new portable haemoglobinometer, Hemo_Control (EKF-diagnostic, GmbH, Germany), which measures haemoglobin concentration in venous and capillary samples. METHOD: The within series and between series imprecision of the Hemo_Control instrument were calculated after measuring the concentration of venous samples under standardized conditions; by experienced laboratory technicians in a hospital laboratory, and venous and capillary samples under conditions similar to where the instrument is intended for use; by personnel at two primary health care centres. The bias of the Hemo_Control instrument was calculated as the difference between its results and results obtained with a Coulter LH 750 instrument traceable to the ICSH reference method. RESULTS: The uncertainty of the Hemo_Control instrument for venous samples was lower than the quality goal of +/- 5% considered acceptable for patient care. High within series imprecision (5.5%) was observed for measurements of capillary blood samples in one of the primary care centres, whereas adequate analytical performance was obtained at the other centre. The Hemo_Control instrument showed negligible bias of +0.8 g/L for both venous and capillary samples in primary health care. CONCLUSION: The observed uncertainty indicates that Hemo_Control is appropriate for near patient testing using venous samples. Capillary samples may be used if sampling skills are adequate.