Cardiometabolic risk factor clustering in patients with deficient branched-chain amino acid catabolism: A case-control study.

Classical organic acidemias (OAs) result from defective mitochondrial catabolism of branched-chain amino acids (BCAAs). Abnormal mitochondrial function relates to oxidative stress, ectopic lipids and insulin resistance (IR). We investigated whether genetically impaired function of mitochondrial BCAA catabolism associates with cardiometabolic risk factors, altered liver and muscle energy metabolism, and IR. In this case-control study, 31 children and young adults with propionic acidemia (PA), methylmalonic acidemia (MMA) or isovaleric acidemia (IVA) were compared with 30 healthy young humans using comprehensive metabolic phenotyping including in vivo 31 P/1 H magnetic resonance spectroscopy of liver and skeletal muscle. Among all OAs, patients with PA exhibited abdominal adiposity, IR, fasting hyperglycaemia and hypertriglyceridemia as well as increased liver fat accumulation, despite dietary energy intake within recommendations for age and sex. In contrast, patients with MMA more frequently featured higher energy intake than recommended and had a different phenotype including hepatomegaly and mildly lower skeletal muscle ATP content. In skeletal muscle of patients with PA, slightly lower inorganic phosphate levels were found. However, hepatic ATP and inorganic phosphate concentrations were not different between all OA patients and controls. In patients with IVA, no abnormalities were detected. Impaired BCAA catabolism in PA, but not in MMA or IVA, was associated with a previously unrecognised, metabolic syndrome-like phenotype with abdominal adiposity potentially resulting from ectopic lipid storage. These findings suggest the need for early cardiometabolic risk factor screening in PA.

Aspects of Newborn Screening in Isovaleric Acidemia.

Isovaleric acidemia (IVA), an inborn error of leucine catabolism, is caused by mutations in the isovaleryl-CoA dehydrogenase (IVD) gene, resulting in the accumulation of derivatives of isovaleryl-CoA including isovaleryl (C5)-carnitine, the marker metabolite used for newborn screening (NBS). The inclusion of IVA in NBS programs in many countries has broadened knowledge of the variability of the condition, whereas prior to NBS, two distinct clinical phenotypes were known, an "acute neonatal" and a "chronic intermittent" form. An additional biochemically mild and potentially asymptomatic form of IVA and its association with a common missense mutation, c.932C>T (p.A282V), was discovered in subjects identified through NBS. Deficiency of short/branched chain specific acyl-CoA dehydrogenase (2-methylbutyryl-CoA dehydrogenase), a defect of isoleucine degradation whose clinical significance remains unclear, also results in elevated C5-carnitine, and may therefore be detected by NBS for IVA. Treatment strategies for the long-term management of symptomatic IVA comprise the prevention of catabolism, dietary restriction of natural protein or leucine intake, and supplementation with l-carnitine and/or l-glycine. Recommendations on how to counsel and manage individuals with the mild phenotype detected by NBS are required.

Human heterologous liver cells transiently improve hyperammonemia and ureagenesis in individuals with severe urea cycle disorders.

BACKGROUND: Urea cycle disorders (UCDs) still have a poor prognosis despite several therapeutic advancements. As liver transplantation can provide a cure, liver cell therapy (LCT) might be a new therapeutic option in these patients. METHODS: Twelve patients with severe UCDs were included in this prospective clinical trial. Patients received up to six infusions of cryopreserved human heterologous liver cells via a surgically placed catheter in the portal vein. Portal vein pressure, portal vein flow, and vital signs were monitored continuously. Calcineurin inhibitors and steroids were used for immunosuppression. In four patients, ureagenesis was determined with stable isotopes. Number and severity of hyperammonemic events and side effects of immunosuppression were analyzed during an observation period of up to 2 years. RESULTS: No study-related mortality was observed. The application catheter dislocated in two children. No significant side effects of catheter application or cell infusion were noted in the other ten patients. The overall incidence of infections did not differ significantly from a historical control group, and no specific side effects of immunosuppression were found. Seven patients were treated per protocol and could be analyzed for efficacy. Severe metabolic crises could be prevented in all of these patients, moderate crises in four of seven. Ureagenesis increased after cell infusion in all patients investigated. CONCLUSIONS: We found a favorable safety profile with respect to catheter placement, intraportal liver cell infusion, and immunosuppression. More than half of the children treated per protocol experienced metabolic stabilization and could be safely bridged to liver transplantation.

Clinical presentation and outcome in a series of 32 patients with 2-methylacetoacetyl-coenzyme A thiolase (MAT) deficiency.

2-methylacetoacetyl-coenzyme A thiolase (MAT) deficiency, also known as beta-ketothiolase deficiency, is an inborn error of ketone body utilization and isoleucine catabolism. It is caused by mutations in the ACAT1 gene and may present with metabolic ketoacidosis. In order to obtain a more comprehensive view on this disease, we have collected clinical and biochemical data as well as information on ACAT1 mutations of 32 patients from 12 metabolic centers in five countries. Patients were between 23months and 27years old, more than half of them were offspring of a consanguineous union. 63% of the study participants presented with a metabolic decompensation while most others were identified via newborn screening or family studies. In symptomatic patients, age at manifestation ranged between 5months and 6.8years. Only 7% developed a major mental disability while the vast majority was cognitively normal. More than one third of the identified mutations in ACAT1 are intronic mutations which are expected to disturb splicing. We identified several novel mutations but, in agreement with previous reports, no clear genotype-phenotype correlation could be found. Our study underlines that the prognosis in MAT deficiency is good and MAT deficient individuals may remain asymptomatic, if diagnosed early and preventive measures are applied.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: Clinical presentation and outcome in a series of 37 patients.

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is a rare inborn error of ketone body synthesis and leucine degradation, caused by mutations in the HMGCL gene. In order to obtain a comprehensive view on this disease, we have collected clinical and biochemical data as well as information on HMGCL mutations of 37 patients (35 families) from metabolic centers in Belgium, Germany, The Netherlands, Switzerland, and Turkey. All patients were symptomatic at some stage with 94% presenting with an acute metabolic decompensation. In 50% of the patients, the disorder manifested neonatally, mostly within the first days of life. Only 8% of patients presented after one year of age. Six patients died prior to data collection. Long-term neurological complications were common. Half of the patients had a normal cognitive development while the remainder showed psychomotor deficits. We identified seven novel HMGCL mutations. In agreement with previous reports, no clear genotype-phenotype correlation could be found. This is the largest cohort of HMGCLD patients reported so far, demonstrating that HMGCLD is a potentially life-threatening disease with variable clinical outcome. Our findings suggest that the clinical course of HMGCLD cannot be predicted accurately from HMGCL genotype. The overall outcome in HMGCLD appears limited, thus rendering early diagnosis and strict avoidance of metabolic crises important.

Living with Intoxication-Type Inborn Errors of Metabolism: A Qualitative Analysis of Interviews with Paediatric Patients and Their Parents.

INTRODUCTION: Progress in diagnosis and treatment of patients with intoxication-type inborn errors of metabolism (IT-IEM) such as urea cycle disorders, organic acidurias or maple syrup urine disease is resulting in a growing number of long-term survivors. Consequently, health-related quality of life (HrQoL) of patients is increasingly regarded as a meaningful outcome parameter. To develop the first validated, disease-specific HrQoL questionnaire for IT-IEM, patients and parents were interviewed as content experts to identify major physical and psychosocial constraints and resources. METHODS: Focus group interviews with 19 paediatric IT-IEM patients and 26 parents were conducted in four metabolic centres in Austria, Germany and Switzerland. Disease-specific HrQoL categories were established by qualitative content analysis. RESULTS: Fourteen disease-specific topics related to the three well-established generic HrQoL dimensions of physical, mental and social functioning were derived from the interview transcripts. Both patients and parents perceived dietary restrictions and social stigmatisation as major burdens. Dietary restrictions and emotional burdens were more important for young (<8 years) patients, whereas cognition, fatigue and social issues were more relevant to older patients (≥8 years). Treatment-related topics had a significant effect on social and emotional HrQoL. DISCUSSION: By exploring patients' and parents' perspectives, 14 HrQoL categories were identified. These new categories will allow the development of a disease-specific, standardised questionnaire to assess HrQoL in paediatric IT-IEM patients. Age-appropriate information on the disease and psychosocial support targeted to patients' individual burdens are essential to the delivery of personalised care that takes account of physical, mental and social dimensions of HrQoL.

Disease control via intensified lipoprotein apheresis in three siblings with familial hypercholesterolemia.

BACKGROUND: Familial hypercholesterolemia (FH), the prevalent monogenic form of hypercholesterolemia, carries the risk of premature coronary heart disease. Lipoprotein-apheresis is established in children with severe dyslipidemia. We present 3 siblings with a negative/negative residual low-density lipoprotein (LDL) receptor mutation (p.Trp577Arg), unresponsive to drug treatment. OBJECTIVE: Intensified lipoprotein-apheresis is well tolerated and results in permanently low lipid values without harming the health-related quality of life in children. METHODS: Three homozygous FH siblings, aged 7-13 years, had been treated with statins and ezetimibe for 12 months but still showed highly elevated low-density lipoprotein cholesterol (LDL-C) plasma concentrations. They were started on double-filtration plasmapheresis that was subsequently intensified according to plasma lipid levels. RESULTS: Each lipoprotein apheresis session reduced LDL-C concentration by 66% to 70%. Treated plasma volume was doubled after 6 months due to a sustained rebound of LDL-C between sessions. However, the rebound remained unchanged. Only an increase in frequency of sessions to every 3 to 4 days resulted in acceptable pre-treatment LDL-C concentrations (Cmax). Neither cessation of statins nor reduction of plasma exchange volume to 1.5 fold in follow-up influenced Cmax. Intensified therapy did not harm health-related quality of life as assessed by PedsQL and was well tolerated. CONCLUSIONS: In pediatric FH patients unresponsive to drug treatment, intensified lipoprotein apheresis can normalize plasma lipid levels. Apparently, treatment frequency rather than volume has greater influence on its efficacy. The potential burden of intensified therapy to daily life has to be regarded. Serum lipid levels in FH should be normalized to minimize cardiovascular risk.

Clinical phenotype, biochemical profile, and treatment in 19 patients with arginase 1 deficiency.

BACKGROUND: Arginase 1 (ARG1) deficiency is a rare urea cycle disorder (UCD). This hypothesis-generating study explored clinical phenotypes, metabolic profiles, molecular genetics, and treatment approaches in a cohort of children and adults with ARG1 deficiency to add to our understanding of the underlying pathophysiology. METHODS: Clinical data were retrieved retrospectively from physicians using a questionnaire survey. Plasma aminoacids, guanidinoacetate (GAA), parameters indicating oxidative stress and nitric oxide (NO) synthesis as well as asymmetric dimethylarginine (ADMA) were measured at a single study site. RESULTS: Nineteen individuals with ARG1 deficiency and 19 matched controls were included in the study. In patients, paraparesis, cognitive impairment, and seizures were significantly associated suggesting a shared underlying pathophysiology. In patients plasma GAA exceeded normal ranges and plasma ADMA was significantly elevated. Compared to controls, nitrate was significantly higher, and the nitrite:nitrate ratio significantly lower in subjects with ARG1 deficiency suggesting an advantage for NO synthesis by inducible NO synthase (iNOS) over endothelial NOS (eNOS). Logistic regression revealed no significant impact of any of the biochemical parameters (including arginine, nitrates, ADMA, GAA, oxidative stress) or protein restriction on long-term outcome. CONCLUSION: Three main hypotheses which must be evaluated in a hypothesis driven confirmatory study are delineated from this study: 1) clinical manifestations in ARG1 deficiency are not correlated with arginine, protein intake, ADMA, nitrates or oxidative stress. 2) GAA is elevated and may be a marker or an active part of the pathophysiology of ARG1 deficiency. 3) Perturbations of NO metabolism merit future attention in ARG1 deficiency.

Malonic aciduria: long-term follow-up of new patients detected by newborn screening.

UNLABELLED: Malonic aciduria is an extremely rare autosomal recessive inborn error of metabolism. We present clinical, biochemical and genetic information for several years of follow-up of new malonic aciduria patients who were diagnosed by newborn screening. These data are discussed with regard to treatment options and possible diagnostic pitfalls. The cases presented here show that the course of malonic aciduria is unpredictable and can even significantly differ in two siblings harbouring identical mutations. Early treatment can lead to the rapid improvement of cardiomyopathy in the course of malonic aciduria. Biochemical parameters seem to be variable and can intermittently be undetectable in the blood or urine samples of affected patients. Therefore, confirmatory tests following a positive newborn screening should be taken with caution and include both malonyl carnitine detection in dried blood spots and urinary organic acid analysis as initial measures. CONCLUSION: Patients with a suspected or confirmed diagnosis of malonic aciduria should undergo thorough diagnostic procedures and be regularly screened for complications such as cardiomyopathy even when they are asymptomatic in order to ensure early therapy of treatable complications.

Guanidinoacetate methyltransferase (GAMT) deficiency: outcomes in 48 individuals and recommendations for diagnosis, treatment and monitoring.

We collected data on 48 patients from 38 families with guanidinoacetate methyltransferase (GAMT) deficiency. Global developmental delay/intellectual disability (DD/ID) with speech/language delay and behavioral problems as the most affected domains was present in 44 participants, with additional epilepsy present in 35 and movement disorder in 13. Treatment regimens included various combinations/dosages of creatine-monohydrate, l-ornithine, sodium benzoate and protein/arginine restricted diets. The median age at treatment initiation was 25.5 and 39 months in patients with mild and moderate DD/ID, respectively, and 11 years in patients with severe DD/ID. Increase of cerebral creatine and decrease of plasma/CSF guanidinoacetate levels were achieved by supplementation with creatine-monohydrate combined with high dosages of l-ornithine and/or an arginine-restricted diet (250 mg/kg/d l-arginine). Therapy was associated with improvement or stabilization of symptoms in all of the symptomatic cases. The 4 patients treated younger than 9 months had normal or almost normal developmental outcomes. One with inconsistent compliance had a borderline IQ at age 8.6 years. An observational GAMT database will be essential to identify the best treatment to reduce plasma guanidinoacetate levels and improve long-term outcomes.

Synergistic mutations in SLC3A1 and SLC7A9 leading to heterogeneous cystinuria phenotypes: pitfalls in the diagnostic workup.

BACKGROUND: Cystinuria is an inherited disorder of a renal tubular amino acid transporter and leads to increased cystine excretion with the risk of urinary stone formation. Phenotypical classification is based on urinary amino acid concentration as type I (silent), type non-I (hyper-excretors), mixed or untyped. Genotypic classification is based on mutations in SLC3A1 (type A) or SLC7A9 (type B). CASE-DIAGNOSIS/TREATMENT: We present six family members with a complex phenotypic profile based on mutations in both genes. The index patient presents a known homozygous mutation (p.T189M) in SLC3A1 and a homozygous mutation (c.225C > T) in SLC7A9. Based on a bioinformatics analysis and published findings, we considered p.T189M to be pathogenic and initially classified c.225C > T as a silent variant. However, segregation analysis detected homozygosity for p.T189M also in non-affected individuals, whereas homozygous c.225C > T segregated with the phenotype. RNA studies confirmed c.225C > T to cause aberrant splicing. CONCLUSIONS: Based on our findings, we conclude that c.225C > T in SLC7A9 determines the clinical phenotype in this family, whereas additional SLC3A1 mutations aggravate the phenotype in heterozygotes for c.225C > T in SLC7A9 without resulting in cystinuria in the homozygous state. Our results underline the need for careful biochemical characterization of family members of an index case of cystinuria. Genetic analysis of both cystinuria genes may be necessary due to the synergistic effects of mutations in two genes.

Elevation of guanidinoacetate in newborn dried blood spots and impact of early treatment in GAMT deficiency.

Guanidinoacetate methyltransferase (GAMT) deficiency is a good candidate disorder for newborn screening because early treatment appears to improve outcomes. We report elevation of guanidinoacetate in archived newborn dried blood spots for 3 cases (2 families) of GAMT deficiency compared with an unaffected carrier and controls. We also report a new case of a patient treated from birth with normal developmental outcome at the age of 42 months.

Liver cirrhosis in glycogen storage disease Ib.

Glycogen storage disease Ib is an inborn error of carbohydrate metabolism leading to impaired glycogenolysis and gluconeogenesis. Cardinal symptoms include fasting hypoglycemia, lactic acidosis and hepatomegaly as well as neutropenia. We report for the first time on the development of liver cirrhosis in a nine-year-old boy in the course of glycogen storage disease Ib and discuss possible underlying pathomechanisms.

Complementary dietary treatment using lysine-free, arginine-fortified amino acid supplements in glutaric aciduria type I - A decade of experience.

The cerebral formation and entrapment of neurotoxic dicarboxylic metabolites (glutaryl-CoA, glutaric and 3-hydroxyglutaric acid) are considered to be important pathomechanisms of striatal injury in glutaric aciduria type I (GA-I). The quantitatively most important precursor of these metabolites is lysine. Recommended therapeutic interventions aim to reduce lysine oxidation (low lysine diet, emergency treatment to minimize catabolism) and to enhance physiologic detoxification of glutaryl-CoA via formation of glutarylcarnitine (carnitine supplementation). It has been recently shown in Gcdh(-/-) mice that cerebral lysine influx and oxidation can be modulated by arginine which competes with lysine for transport at the blood-brain barrier and the inner mitochondrial membrane [Sauer et al., Brain 134 (2011) 157-170]. Furthermore, short-term outcome of 12 children receiving arginine-fortified diet showed very promising results [Strauss et al., Mol. Genet. Metab. 104 (2011) 93-106]. Since lysine-free, arginine-fortified amino acid supplements (AAS) are commercially available and used in Germany for more than a decade, we evaluated the effect of arginine supplementation in a cohort of 34 neonatally diagnosed GA-I patients (median age, 7.43 years; cumulative follow-up period, 221.6 patient years) who received metabolic treatment according to a published guideline [Kölker et al., J. Inherit. Metab. Dis. 30 (2007) 5-22]. Patients used one of two AAS product lines during the first year of life, resulting in differences in arginine consumption [group 1 (Milupa Metabolics): mean=111 mg arginine/kg; group 2 (Nutricia): mean=145 mg arginine/kg; p<0.001]. However, in both groups the daily arginine intake was increased (mean, 137 mg/kg body weight) and the dietary lysine-to-arginine ratio was decreased (mean, 0.7) compared to infants receiving human milk and other natural foods only. All other dietary parameters were in the same range. Despite significantly different arginine intake, the plasma lysine-to-arginine ratio did not differ in both groups. Frequency of dystonia was low (group 1: 12.5%; group 2: 8%) compared with patients not being treated according to the guideline, and gross motor development was similar in both groups. In conclusion, the development of complementary dietary strategies exploiting transport competition between lysine and arginine for treatment of GA-I seems promising. More work is required to understand neuroprotective mechanisms of arginine, to develop dietary recommendations for arginine and to evaluate the usefulness of plasma monitoring for lysine and arginine levels as predictors of cerebral lysine influx.

Plugs in nuclear pores: transcripts in early oocyte development identified with nanotechniques.

Throughout oogenesis, huge amounts of RNA are produced that are needed for early development. Early stages of oocyte development are characterized by high transcriptional activity whereas translation of maternal RNA dominates late stages. Nuclear pore complexes (NPCs), located in the nuclear envelope (NE), mediate bidirectional macromolecule exchange between the nuclear and cytosolic compartments including RNA export. Here, we report on structural correlates of this transport pathway at single NPC level. Using atomic force microscopy (AFM), we imaged the nucleoplasmic ("inner") surface of the NE of Xenopus laevis oocytes in different stages of development. We found that NPC frequency per nucleus increases with maturation. However, individual NPCs are more active in immature stages. In early stages, known for high transcriptional activity, we found nearly 10% of NPC central channels plugged with a 400-800 kDa mass. In contrast, the incidence of plugged NPCs was below 1% in late oocyte stages. On-site RNA digestion led to a change in plug shape from prominent to flat while plug mass decreased by almost 20%. Quantitative AFM analysis revealed that RNase exposure reduced total nucleoplasmic NPC mass by about 58 and 25% in early and late stage oocytes, respectively. We conclude: (i) NPCs of immature oocytes are more active in RNA transport, (ii) Plugs identified at the nucleoplasmic entrance of NPC central channels represent ribonucleoproteins exiting the nucleus, (iii) RNA is a structural component of the NPC nanomachine.