Insulin-resistant hyperglycaemia complicating neonatal onset of methylmalonic and propionic acidaemias

Pathophysiological mechanisms of complications associated with propionic acidemia

Propionic acidemia (PA) is a genetic metabolic disorder caused by mutations in the mitochondrial enzyme, propionyl-CoA carboxylase (PCC), which is responsible for converting propionyl-CoA to methylmalonyl-CoA for further metabolism in the tricarboxylic acid cycle. When this process is disrupted, propionyl-CoA and its metabolites accumulate, leading to a variety of complications including life-threatening cardiac diseases and other metabolic strokes. While the clinical symptoms and diagnosis of PA are well established, the underlying pathophysiological mechanisms of PA-induced diseases are not fully understood. As a result, there are currently few effective therapies for PA beyond dietary restriction. This review focuses on the pathophysiological mechanisms of the various complications associated with PA, drawing on extensive research and clinical reports. Most research suggests that propionyl-CoA and its metabolites can impair mitochondrial energy metabolism and cause cellular damage by inducing oxidative stress. However, direct evidence from in vivo studies is still lacking. Additionally, elevated levels of ammonia can be toxic, although not all PA patients develop hyperammonemia. The discovery of pathophysiological mechanisms underlying various complications associated with PA can aid in the development of more effective therapeutic treatments. The consequences of elevated odd-chain fatty acids in lipid metabolism and potential gene expression changes mediated by histone propionylation also warrant further investigation.

Insights into energy balance dysregulation from a mouse model of methylmalonic aciduria

Inherited disorders of mitochondrial metabolism, including isolated methylmalonic aciduria, present unique challenges to energetic homeostasis by disrupting energy-producing pathways. To better understand global responses to energy shortage, we investigated a hemizygous mouse model of methylmalonyl-CoA mutase (Mmut)-type methylmalonic aciduria. We found Mmut mutant mice to have reduced appetite, energy expenditure and body mass compared with littermate controls, along with a relative reduction in lean mass but increase in fat mass. Brown adipose tissue showed a process of whitening, in line with lower body surface temperature and lesser ability to cope with cold challenge. Mutant mice had dysregulated plasma glucose, delayed glucose clearance and a lesser ability to regulate energy sources when switching from the fed to fasted state, while liver investigations indicated metabolite accumulation and altered expression of peroxisome proliferator-activated receptor and Fgf21-controlled pathways. Together, these shed light on the mechanisms and adaptations behind energy imbalance in methylmalonic aciduria and provide insight into metabolic responses to chronic energy shortage, which may have important implications for disease understanding and patient management.

Transient Insulin Resistance in Propionic Acidaemia: Knowing is half the battle

Propionic acidaemia (PPA) is a disorder of amino acid and odd-chain fatty acid metabolism. Hypoglycaemia is a more commonly described finding rather than hyperglycaemia during metabolic decompensation of PPA. There is a high mortality rate in patients with organic acidaemias having severe insulin-resistant hyperglycaemia. We report a nine-month-old boy with PPA who was admitted to tertiary care hospital in Muscat, Oman, in 2018 with metabolic decompensation, persistent hyperglycaemia and transient insulin resistance. Hyperglycaemia did not respond to high insulin infusion. Plasma glucose only improved when glucose infusion rate (GIR) reached 7 mg/kg/min. The patient has full recovery and was discharged, with follow up plan. It is important to balance the GIR to achieve the targeted insulin level, beyond which the risks of hyperglycaemia start to outweigh the potential anabolic benefits of additional insulin secretion. Timely clinical attention should be given to achieve adequate caloric delivery through alternative sources other than high GIR to permit better glycaemic control, especially when insulin-resistant hyperglycaemia is present.

REVIEW: Practical strategies to maintain anabolism by intravenous nutritional management in children with inborn metabolic diseases

One of the most vital elements of management for patients with inborn errors of intermediary metabolism is the promotion of anabolism, the state in which the body builds new components, and avoidance of catabolism, the state in which the body breaks down its own stores for energy. Anabolism is maintained through the provision of a sufficient supply of substrates for energy, as well as critical building blocks of essential amino acids, essential fatty acids, and vitamins for synthetic function and growth. Patients with metabolic diseases are at risk for decompensation during prolonged fasting, which often occurs during illnesses in which enteral intake is compromised. During these times, intravenous nutrition must be supplied to fully meet the specific nutritional needs of the patient. We detail our approach to intravenous management for metabolic patients and its underlying rationale. This generally entails a combination of intravenous glucose and lipid as well as early introduction of protein and essential vitamins. We exemplify the utility of our approach in case studies, as well as scenarios and specific disorders which require a more careful administration of nutritional substrates or a modification of macronutrient ratios.

Mutation analysis of genes related to methylmalonic acidemia: identification of eight novel mutations

Methylmalonic acidemia (MMA), an inherited metabolic disease, results from genetic defects in methylmalonyl-CoA mutase or any of the proteins involved in adenosylcobalamin synthesis. This enzyme is classified into several complementation groups and genotypic classes. In this work we explain the biochemical, structural and genetic analysis of 25 MMA patients, from Iran. The diagnosis was established by the measurement of propionylcarnitine in blood using tandem mass spectrometry and confirmed using a gas chromatography-flame ionization detector. Using clinical, biochemical, structural and molecular analyses we identified 15 mut MMA, three cblA, one cblB, and four cblC-deficient patients. Among mutations identified in the MUT gene (MUT) only one, the c.1874A>C (p.D625A) variant, is likely a mut^- mutation. The remaining mutations are probably mut⁰. Here, we present the first molecular analysis of MMA in Iranian patients and have identified eight novel mutations. Four novel mutations (p.D625A, p.R326G, p.V157F, p.F379L) were seen exclusively in patients from northern Iran. One novel splice site mutation (c.2125-3C>G) in MUT and two novel mutation (p.N225M and p.A99P) in the MMAA gene were associated with patients from eastern Iran. The rs184829210 SNP was recognized only in patients with the novel c.958G>A (p.A320T) mutation. This study confirms pathogenesis of deficient enzyme activity in MUT, MMAA, MMAB, and MMACHC as previous observations. These results could act as a basis for the performance of pharmacological therapies for increasing the activity of proteins derived from these mutations.

Eight novel MUT loss-of-function missense mutations in Chinese patients with isolated methylmalonic academia

BACKGROUND

Isolated methylmalonic acidemia is a rare autosomal recessive metabolic disorder mostly caused by mutations in the methylmalonyl coenzyme A mutase (MCM) gene (MUT). This study aimed to verify whether missense mutations in MUT in Chinese patients affect the stability and enzymatic activity of MCM.

METHODS

Eight Chinese patients were identified with novel mutations. Plasmids carrying the wild-type and mutated MUT cDNA were constructed and transfected into HEK293T cells for functional analyses. The expression and activity of MCM were determined by western blot and ultra-performance liquid chromatography, respectively.

RESULTS

All patients had high levels of blood propionylcarnitine and urinary methylmalonyl acid. By the end of the study, two patients were lost to follow-up, three died, and three survived with mental retardation. Compared to the wild-type protein, the expression levels of all missense mutations of in vitro MCM protein were decreased (P<0.05) except those for I597R, and the MCM activity of the mutations was reduced in a permissive assay.

CONCLUSIONS

The missense mutations L140P, A141T, G161V, W309G, I505T, Q514K, I597R and G723D affected the stability and enzymatic activity of MCM, indicating that they had a disease-causing capacity.

The long-term treatment of a patient with type 1 diabetes mellitus and glutaric aciduria type 1: the effect of insulin

The coexistence of two diseases associated with different metabolic disorders is a very rare event. Some associations, although sporadic, can be particularly challenging both in terms of diagnostic and therapeutic management and in terms of theoretical perspective. Here, we report a child affected by type 1 diabetes mellitus (T1DM) and glutaric aciduria type 1 (GA1). The child was diagnosed with classical T1DM at 15 months of age, with a tendency toward hypoglycemia. A few months later, during an acute intercurrent infective episode, the child displayed acute hypotonia of the lower limbs and limbs dystonia. A brain MRI showed bilateral striatal necrosis, suggesting GA1 diagnosis. Treatment with a low-lysine dietary regimen and carnitine supplementation was started and resulted in an improvement in metabolic control and a reduction of hypoglycemic episodes along with an increasing in insulin daily dose. After 2 years, the neurological outcome consisted of a reduction in dystonic movements and a metabolic stability of both diseases.

CONCLUSION

This case provides some insight into the reciprocal interconnections between the two metabolic disorders. Similar pathogenic mechanisms responsible for the neuronal injury might have impacted each other, and a strict relationship between a specific aspect of GA1-impaired metabolism and glucose homeostasis might explain how the tailored management of GA1 was not only effective in controlling the disease, but it also resulted in an improvement in the control of the glycemic profile. What in known: • Glutaric aciduria type 1 (GA1) usually presents in childhood with severe and possibly irreversible neuronal damage, triggered by a catabolic stress • The association of GA1 with other diseases, including type 1 diabetes mellitus (T1DM), is a rare event, complicating the treatment management What is new: • Insulin treatment has a role in preventing GA1 metabolic decompensation, even in the catabolic condition of hypoglycemia • Promoting GA1 metabolic equilibrium by tailoring drug and dietary treatment in our patient affect by T1DM has a positive impact also in improving glycemic balance.

High glucose intake and glycaemic level in critically ill neonates with inherited metabolic disorders of intoxication

To investigate glycaemic levels in critically ill neonates with inherited metabolic disorders of intoxication. Thirty-nine neonates with a median age of 7 days (0-24) were retrospectively included (urea cycle disorders (n = 18), maple syrup disease (n = 13), organic acidemias (n = 8)). Twenty-seven neonates were intubated, 21 were haemodialysed and 6 died. During the first 3 days, median total and peak blood glucose (BG) levels were 7.1 mmol/L (0.9-50) and 10 mmol/L (5.1-50), respectively. The median glucose intake rate was 11 mg/kg/min (2.7-15.9). Fifteen and 23 neonates exhibited severe hyperglycaemia (≥2 BG levels >12 mmol/L) and mild hyperglycaemia (≥2 BG levels >7 and ≤12 mmol/L), respectively. Glycaemic levels and number of hyperglycaemic neonates decreased over the first 3 days (p < 0.001) while total glucose intake rate was stable (p = 0.11). Enteral route of glucose intake was associated with a lower number of hyperglycaemic neonates (p = 0.04) and glycaemic level (p = 0.02).

CONCLUSION

Hyperglycaemia is common in critically ill neonates receiving high glucose intake with inherited metabolic disorders of intoxication. Physicians should decrease the rate of total glucose intake and begin enteral feeding as quickly as possible in cases of persistent hyperglycaemia.

WHAT IS KNOWN

• The risk of hyperglycaemia in the acute phase of critical illness is high. What is New: • Hyperglycaemia is common in the initial management of critically ill neonates with inherited metabolic disorders of intoxication receiving high glucose intake.

Clinical features and MUT gene mutation spectrum in Chinese patients with isolated methylmalonic acidemia: identification of ten novel allelic variants

BACKGROUND

This study aims to study MUT gene mutation spectrum in Chinese patients with isolated methylmalonic academia (MMA) and their clinical features for the potential genotype-phenotype correlation.

METHODS

Forty-three patients were diagnosed with isolated MMA by elevated blood propionylcarnitine, propionylcarnitine to acetylcarnitine ratio, and urine methylmalonate without hyperhomocysteinemia. The MUT gene was amplified by polymerase chain reaction and directly sequenced. Those patients with at least one variant allele were included. The novel missense mutations were assessed by bioinformatic analysis and screened against alleles sequenced from 50 control participants.

RESULTS

Among the 43 patients, 38 had typical clinical presentations, and the majority (30/38) experienced earlyonset MMA. Eight patients died and seven were lost to follow-up. Twenty patients had poor outcomes and eight showed normal development. The 43 identified MUT gene mutations had at least one variant allele, whereas 35 had two mutant alleles. Of the 33 mutations reported before, eight recurrent mutations were identified in 32 patients, and c.729_730insTT (p.D244Lfs*39) was the most common (12/78) in the mutant alleles. Of the 10 novel mutations, six were missense mutations and four were premature termination codon mutations. The six novel missense mutations seemed to be pathogenic.

CONCLUSIONS

A total of 10 novel MUT mutations were detected in the Chinese population. c.729_730insTT (p.D244Lfs*39) was the most frequent mutation. A genotype-phenotype correlation could not be found, but the genotypic characterization indicated the need of genetic counseling for MMA patients and early prenatal diagnoses for high-risk families.

Defect of cobalamin intracellular metabolism presenting as diabetic ketoacidosis: a rare manifestation

Hypoglycemia is the usual feature of commonly occurring organic acidemias. Organic acidemias manifesting as hyperglycemia or diabetic ketoacidosis are rare and only a few cases have been reported. We report a 13-month-old boy who presented with vomiting, dehydration, coma, hyperglycemia, high anion gap metabolic acidosis and ketosis, mimicking diabetic ketoacidosis (DKA). Treatment with parenteral fluid, electrolytes, and insulin infusion resulted in an improvement in hyperglycemia, but persistence of metabolic acidosis and lack of improvement of neurologic status led us to suspect an organic acidemia. Urinary organic acid analysis revealed increased methylmalonic acid levels. In addition, hyperhomocysteinemia and homocystinuria were also noted in presence of normal vitamin B12 levels. This confirmed the diagnosis of cobalamin metabolism defect leading to combined methylmalonic aciduria and homocystinuria. There was some improvement in neurologic status and metabolic parameters after treatment with low-protein diet, vitamin B12, folic acid, and L-carnitine, but he ultimately succumbed to polymicrobial nosocomial sepsis. The entire MMACHC gene of the patient was sequenced and no mutations were identified. This is probably the first case report of cobalamin intracellular metabolism defect (CblC/CblD/CblF/CblJ or ABCD4) presenting as diabetic ketoacidosis.

Natural history of propionic acidemia

Propionic acidemia is an organic acidemia that can lead to metabolic acidosis, coma and death, if not treated appropriately in the acute setting. Recent advancements in treatment have allowed patients with propionic acidemia to live beyond the neonatal period and acute presentation. The natural history of the disease is just beginning to be elucidated as individuals reach older ages. Recent studies have identified the genomic mutations in the genes PCCA and PCCB. However, as of yet no clear genotype-phenotype correlations are known. As patients age, the natural progression of propionic acidemia illuminates intellectual difficulties, increased risk for neurological complications, including stroke-like episodes, cardiac complications, and gastrointestinal difficulties, as well as a number of other complications. This article reviews the available literature for the natural history of propionic acidemia.