Lethal late onset cblB methylmalonic aciduria

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.

Clinical and molecular findings in 37 Turkish patients with isolated methylmalonic acidemia

Background/aim

Isolated methylmalonic acidemia (MMA) is caused by complete or partial deficiency of the enzyme methylmalonyl- CoA mutase (mut0 or mut– enzymatic subtype), a defect of its cofactor adenosyl-cobalamin (cblA, cblB, or cblD-MMA), or deficiency of the enzyme methylmalonyl-CoA epimerase. While onset of the disease ranges from the neonatal period to adulthood, most cases present with lethargy, vomiting and ketoacidosis in the early infancy. Major secondary complications are; growth failure, developmental delay, interstitial nephritis with progressive renal failure, basal ganglia injury and cardiomyopathy. We aimed to demonstrate clinical and molecular findings based on long-term follow up in our patient cohort.

Materials and methods

The study includes 37 Turkish patients with isolated MMA who were followed up for long term complications 1 to 14 years. All patients were followed up regularly with clinical, biochemical and dietary monitoring to determine long term complications. Next Generation Sequencing technique was used for mutation screening in five disease-causing genes including; MUT, MMAA, MMAB, MMADHC, MCEE genes. Mutation screening identified 30 different types of mutations.

Results

While 28 of these mutations were previously reported, one novel MMAA mutation p.H382Pfs*24 (c.1145delA) and one novel MUT mutation IVS3+1G>T(c.752+1G>T) has been reported. The most common clinical complications were growth retardation, renal involvement, mental motor retardation and developmental delay. Furthermore, one of our patients developed cardiomyopathy, another one died because of hepatic failure and one presented with lactic acidosis after linezolid exposure.

Conclusion

We have detected two novel mutations, including one splice-site mutation in the MUT gene and one frame shift mutation in the MMAA gene in 37 Turkish patients. We confirm the genotype-phenotype correlation in the study population according to the long-term complications.

Isolated methylmalonic acidemia with unusual presentation mimicking diabetic ketoacidosis

BACKGROUND

Hyperglycemic ketoacidosis is an acute, life threatening condition requiring early etiologic recognition and management to prevent serious morbidity/mortality. The most common cause is diabetic ketoacidosis (DKA). Organic acidemias (OAs) are inheritable disorders caused by defects in protein metabolism resulting in acid accumulation. Patients with metabolic decompensation usually present with acidosis, with/without hypoglycemia. Hyperglycemia is a very rare manifestation. At least 16 cases of OAs presenting with hyperglycemia have been reported. Six of the 16 were diagnosed with isolated methylmalonic academia (MMA) and three of the six passed away from late diagnosis.

CASE DESCRIPTION

We describe a 2-year-old Thai girl who presented with hyperglycemia, acidosis and ketosis. She has underlying delayed development, seizures, optic atrophy and poor growth. An initial diagnosis of DKA was made and standard treatment was started. After 4 h of treatment, the patient partially responded to treatment; blood sugar decreased but acidosis and ketonemia persisted. HbA1c was normal. Investigations to rule out OAs were performed. Markedly elevated urinary methylmalonic acid consistent with MMA was observed. Molecular and enzyme analyses confirmed the diagnosis with isolated MMA. Specific treatment for MMA including protein restriction, high caloric fluid, carnitine and vitamin B12 was promptly started. Clinical improvement was seen 4 days after initiating specific treatment.

CONCLUSIONS

Inherited metabolic disorders should be included in differential diagnosis in hyperglycemia ketoacidosis patients who respond poorly to standard DKA treatment. Unusual findings, e.g. hyperammonemia, lactic acidosis, pancytopenia, abnormal basal ganglia in MRI or underlying delayed development may indicate underlying OAs. Determining the etiology of hyperglycemic ketoacidosis is important and can lead to good outcomes.

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.

Methylmalonic acidemia and hyperglycemia: an unusual association

INTRODUCTION

Hyperglycemia is an exceptional manifestation of methylmalonic acidemia (MMA). We describe a patient with MMA in whom we observed a hyperglycemia which improved under treatment of the metabolic crisis.

CASE REPORT

A 14 month-old boy presented with an acute generalized dystonia and lethargy preceded by fever, vomiting and lethargy at the age of 13 months. Biological investigations showed a hyperglycemia, a lactic acidosis and a hyperammonemia. Urinary organic acid analysis showed accumulation of methylmalonic acid, tiglylglycine and methylcitrate leading to the diagnosis of MMA. The patient underwent symptomatic treatment with rapid improvement of general condition, consciousness and gradual normalization of biological parameters especially glycemia after 6 days without using insulinotherapy.

DISCUSSION

MMA is an autosomal recessive disorder caused by a deficiency of methylmalonyl-CoA mutase resulting in methylmalonic acid accumulation. Biochemically, the disorder is typically characterized by: metabolic acidosis, ketonemia or ketonuria, hyperammonemia, leukopenia, thrombocytopenia and anemia. Hypoglycemia is a frequent manifestation of MMA. Our patient presented a hyperglycemia, which is unusual in MMA, since we found only three patients reported with this association. Pathophysiology remains unknown. In reported cases, hyperglycemia was treated by insulin therapy and reducing glucose intravenous infusion, with fatal outcome. In our patient glycemia spontaneously normalized after treatment of the metabolic crisis.

CONCLUSION

Hyperglycemia is an exceptional manifestation of MMA and could be a seriousness marker.

Propionic acidemia mimicking diabetic ketoacidosis

Propionic acidemia manifesting with hyperglycemia is rare. Few cases have been reported mainly of the neonatal-onset form associated with high mortality. We report a 9-month-old Palestinian boy who manifested with coma, severe hyperglycemia and ketoacidosis mimicking diabetic ketoacidosis. Family history of unexplained infant deaths was helpful in reaching the correct diagnosis. In response to therapy, the patient regained consciousness without neurologic deficits and had normal examination. This is, to our knowledge, the first case report of late-onset propionic acidemia that had this presentation and survived.

Multiple roles of ATP:cob(I)alamin adenosyltransferases in the conversion of B12 to coenzyme B12

Our mechanistic understanding of the conversion of vitamin B(12) into coenzyme B(12) (a.k.a. adenosylcobalamin, AdoCbl) has been substantially advanced in recent years. Insights into the multiple roles played by ATP:cob(I)alamin adenosyltransferase (ACA) enzymes have emerged through the crystallographic, spectroscopic, biochemical, and mutational analyses of wild-type and variant proteins. ACA enzymes circumvent the thermodynamic barrier posed by the very low redox potential associated with the reduction of cob(II)alamin to cob(I)alamin by generating a unique four-coordinate cob(II)alamin intermediate that is readily converted to cob(I)alamin by physiological reductants. ACA enzymes not only synthesize AdoCbl but also they deliver it to the enzymes that use it, and in some cases, enzymes in which its function is needed to maintain the fidelity of the AdoCbl delivery process have been identified. Advances in our understanding of ACA enzyme function have provided valuable insights into the role of specific residues, and into why substitutions of these residues have profound negative effects on human health. From an applied science standpoint, a better understanding of the adenosylation reaction may lead to more efficient ways of synthesizing AdoCbl.

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

BACKGROUND

Insulin-resistant hyperglycaemia may occasionally complicate the clinical course of organic acidaemias.

STUDY DESIGN

Clinical observation.

RESULTS

Two term infants, one suffering from acute early-onset methylmalonic acidaemia, the other suffering from acute early-onset propionic acidaemia, presented acutely with dehydration, ketoacidosis, and hyperammonaemia. Urinary organic acid, plasma amino acids, and blood and plasma acylcarnitine analysis allowed the diagnosis of methylmalonic and propionic acidaemias. The detection of the novel c.481G>A (p.Gly161Arg) and the known c.655A>T (p.Asn219Tyr) MUT gene mutations identified the first patient as affected by methylmalonic acidaemia mut type. The high increase of propionylcarnitine after carnitine administration in both patients suggested a greatly elevated metabolic intoxication. Both newborns showed insulin-resistant hyperglycaemia. Patient 1 died, but patient 2, after a strong reduction of glucose administration, survived. To our knowledge, this is the only patient with this complication who survived.

CONCLUSION

Insulin-resistant hyperglycaemia complicating neonatal onset of methylmalonic and propionic acidaemias is probably a marker of a serious disease. One patient with this complication survived after a strong reduction of glucose administration. Even if this is probably only a partial intervention, we hypothesize that in this situation a reduction of glucose administration can reduce almost the risk of persistent hyperglycaemia. Further studies are required to confirm our hypothesis.

Crystallization and preliminary X-ray crystallographic studies of a PduO-type ATP:cob(I)alamin adenosyltransferase from Bacillus cereus

Cobalamin adenosyltransferases transfer a 5'-deoxyadenosyl moiety from ATP and covalently attach it to the cobalt(I) ion of the corrin ring of cobalamin to generate adenosylcobalamin. The PduO-type adenosyltransferase from Bacillus cereus was overexpressed in Escherichia coli, purified and crystallized as the apoenzyme as well as in complex with Mg(2+) and ATP (MgATP). Diffraction data were collected to 1.9 A resolution for the native crystals and 2.0 A resolution for the complexed crystals. Both crystals belonged to the orthorhombic space group C222(1); the native crystals have unit-cell parameters a = 64.93, b = 137.08, c = 158.55 A. The asymmetric unit contained one trimer, with a corresponding V(M) of 2.69 A(3) Da(-1).

Impact of inborn errors of metabolism on admission and mortality in a pediatric intensive care unit

The authors conducted a retrospective analysis of the patients admitted to a pediatric intensive care unit (PICU) during a five-year period, with specific focus on those with a suspected or confirmed diagnosis of inborn errors of metabolism (IEM), in order to ascertain the resources required to care for these patients. Medical records were reviewed for all admissions between January 1998 and December 2002 in a single metabolic referral center, and a subset of patients were identified with suspected IEM at admission or diagnosed IEM at hospital discharge. These patient charts were then further reviewed and the following information was extracted: IEM diagnosis, demographic data, biochemical characteristics at admission, need for mechanical ventilation, use of extracorporeal removal therapy, and outcome at PICU discharge. The study population comprised 70 patients (2.2% of all admissions during the study period) and included 33 neonates and 37 children aged >28 days. IEM diagnosis was known at the time of admission to the PICU in 9/33 of the neonates and 23/37 of the older children. Forty-three of the patients required invasive mechanical ventilation, while continuous extracorporeal removal therapy was used in 27 children. The median length of PICU stay was 3 days (range, 1 to 13 days) and 20 patients (28.6%) died. In conclusion, these observations show that inherited metabolic disease may be as frequent a primary diagnosis as septic shock in some PICUs. In neonates, these diseases are not usually diagnosed prior to PICU admission. Patients with IEM admitted to a PICU require aggressive support (including mechanical ventilation and extracorporeal removal therapies), and consume significant resources for relatively short PICU stays. These patients constitute a significant diagnostic and therapeutic challenge for pediatric intensivists.

Structural characterization of the active site of the PduO-type ATP:Co(I)rrinoid adenosyltransferase from Lactobacillus reuteri

The three-dimensional crystal structure of the PduO-type corrinoid adenosyltransferase from Lactobacillus reuteri (LrPduO) has been solved to 1.68-A resolution. The functional assignment of LrPduO as a corrinoid adenosyltransferase was confirmed by in vivo and in vitro evidence. The enzyme has an apparent Km(ATP) of 2.2 microM and Km(Cobalamin) of 0.13 microM and a kcat of 0.025 s(-1). Co-crystallization of the enzyme with Mg-ATP resulted in well-defined electron density for an N-terminal loop that had been disordered in other PduO-type enzyme structures. This newly defined N-terminal loop makes up the lower portion of the enzyme active site with the other half being contributed from an adjacent subunit. These results provide the first detailed description of the enzyme active site for a PduO-type adenosyltransferase and identify a unique ATP binding motif at the protein N terminus. The molecular architecture at the active site offers valuable new insight into the role of various residues responsible for the human disease methylmalonic aciduria.