Subacute combined degeneration of the spinal cord in cblC disorder despite treatment with B12

Would, early, versus late hydroxocobalamin dose intensification treatment, prevent cognitive decline, macular degeneration and ocular disease, in 5 patients with early-onset cblC deficiency?

In early-onset (EO) cblC deficiency (MMACHC), hydroxocobalamin dose-intensification (OHCBL-DI) improved biochemical and clinical outcome. In mammals, Cobalamin is reduced, in a reaction mediated by MMACHC. Pathogenic variants in MMACHC disrupt the synthesis pathway of methyl-cobalamin (MetCbl) and 5'-deoxy-adenosyl-cobalamin (AdoCbl), cofactors for both methionine synthase (MS) and methyl-malonyl-CoA mutase (MCM) enzymes. In 5 patients (pts.), with EO cblC deficiency, biochemical and clinical responses were studied following OHCbl-DI (mean ± SD 6,5 ± 3,3 mg/kg/day), given early, before age 5 months (pts. 1, 2, 3 and 4) or lately, at age 5 years (pt. 5). In all pts., total homocysteine (tHcy), methyl-malonic acid (MMA) and Cob(III)alamin levels were measured. Follow-up was performed during 74/12 years (pts. 1, 2, 3), 33/12 years (pt. 4) and 34/12 years (pt. 5). OHCbl was delivered intravenously or subcutaneously. Mean ± SD serum Cob(III)alamin levels were 42,2 × 106 ± 28, 0 × 106 pg/ml (normal: 200-900 pg/ml). In all pts., biomarkers were well controlled. All pts., except pt. 5, who had poor vision, had central vision, mild to moderate nystagmus, and with peri-foveolar irregularity in pts. 1, 2 and 4, yet none had the classic bulls' eye maculopathy and retinal degeneration characteristic of pts. with EO cblC deficiency. Only pt. 5, had severe cognitive deficiency. Both visual and cognitive functions were better preserved with early than with late OHCBL-DI. OHCBL-DI is suggested to bypass MMACHC, subsequently to be rescued by methionine synthase reductase (MSR) and adenosyl-transferase (ATR) to obtain Cob(I)alamin resulting in improved cognitive and retinal function in pts. with EO cblC deficiency.

Methylmalonic acidemia: Neurodevelopment and neuroimaging

Methylmalonic acidemia (MMA) is a genetic disease of abnormal organic acid metabolism, which is one of the important factors affecting the survival rate and quality of life of newborns or infants. Early detection and diagnosis are particularly important. The diagnosis of MMA mainly depends on clinical symptoms, newborn screening, biochemical detection, gene sequencing and neuroimaging diagnosis. The accumulation of methylmalonic acid and other metabolites in the body of patients causes brain tissue damage, which can manifest as various degrees of intellectual disability and severe neurological dysfunction. Neuroimaging examination has important clinical significance in the diagnosis and prognosis of MMA. This review mainly reviews the etiology, pathogenesis, and nervous system development, especially the neuroimaging features of MMA.

A rise in cases of nitrous oxide abuse: neurological complications and biological findings

BACKGROUND

The recent lockdown due to the COVID-19 pandemic has been linked to a higher incidence of psychiatric manifestations and substance abuse. The recreative use of nitrous oxide is more and more widespread and neurological complications are frequent.

METHODS

We report clinical characteristics and biological findings of five consecutive patients presenting to our tertiary care center between April 2020 and February 2021 with various neurological symptoms occurring after recent nitrous oxide abuse.

RESULTS

Our patients presented with subacute combined degeneration of the spinal cord (4/5 patients) or with acute inflammatory demyelinating polyneuropathy (1/5 patients). No patient had reduced vitamin B-12 titer, but all had elevated blood levels of homocysteine and methylmalonic acid. This reflects the functional deficit in vitamin B-12 that can be linked to nitrous oxide consumption. After vitamin B-12 supplementation, clinical signs regressed at least partially in all 5 patients.

CONCLUSION

We report an elevated incidence of neurological complications of nitrous oxide abuse occurring during the recent COVID-19 lockdown. Nitrous oxide abuse should be tracked down in patients presenting with compatible neurological symptoms and elevated homocysteinemia. Vitamin B-12 should be supplemented as soon as the diagnosis is made.

Adolescent/adult-onset homocysteine remethylation disorders characterized by gait disturbance with/without psychiatric symptoms and cognitive decline: a series of seven cases

Homocysteine remethylation disorders are rare inherited disorders caused by a deficient activity of the enzymes involved in the remethylation of homocysteine to methionine. The adolescent/adult-onset remethylation disorders are rarely reported. We analyzed the clinical and genetic characteristics of seven cases with adolescent/adult remethylation disorders, including 5 cases of the cobalamin C disease (cblC) and 2 cases of the methylenetetrahydrofolate reductase deficiency. The average onset age was 21.1 (range 14 to 40) years. All patients complained of gait disturbances. Other common symptoms included psychiatric symptoms (5/7) and cognitive decline (4/7). Acute encephalopathy, dysarthria, anorexia, vomiting, ketoacidosis, anemia, cataract, and hand tremor were also observed. The mean total homocysteine in serum when the patients were diagnosed was 94.6 (range 53.1-154.5) mol/L. Electrophysiological studies revealed neuropathy in the lower limbs (6/7). The brain MRI showed reversible altered signal from the dorsal portions of the cerebellar hemispheres (1/7), periventricular hyperintensity (2/7), and delayed/impaired myelination (2/7). The sural nerve biopsy performed in one case showed a modest loss of myelinated fibers. Five patients showed heterozygous mutations of the MMACHC gene, including c.482G>A (5/5), c.609G>A (2/5), and c.658-660delAAG (3/5). Two patients showed heterozygous mutations of the MTHFR gene, including c.698C>A (2/2), c.698C>G (1/2), and c.236+1G>A (1/2). The patients responded well to the treatments with significant improvements. Adolescent/adult-onset remethylation disorders are easily misdiagnosed. We recommend testing the serum homocysteine concentrations in young/adult patients with unexplained neuro-psychotic symptoms. Furthermore, individuals with significantly elevated serum homocysteine concentrations should be further tested by organic acid screening and genetic analysis.

The vitamin B12 processing enzyme, mmachc, is essential for zebrafish survival, growth and retinal morphology

Cobalamin C (cblC) deficiency, the most common inborn error of intracellular cobalamin metabolism, is caused by mutations in MMACHC, a gene responsible for the processing and intracellular trafficking of vitamin B12. This recessive disorder is characterized by a failure to metabolize cobalamin into adenosyl- and methylcobalamin, which results in the biochemical perturbations of methylmalonic acidemia, hyperhomocysteinemia and hypomethioninemia caused by the impaired activity of the downstream enzymes, methylmalonyl-CoA mutase and methionine synthase. Cobalamin C deficiency can be accompanied by a wide spectrum of clinical manifestations, including progressive blindness, and, in mice, manifests with very early embryonic lethality. Because zebrafish harbor a full complement of cobalamin metabolic enzymes, we used genome editing to study the loss of mmachc function and to develop the first viable animal model of cblC deficiency. mmachc mutants survived the embryonic period but perished in early juvenile life. The mutants displayed the metabolic and clinical features of cblC deficiency including methylmalonic acidemia, severe growth retardation and lethality. Morphologic and metabolic parameters improved when the mutants were raised in water supplemented with small molecules used to treat patients, including hydroxocobalamin, methylcobalamin, methionine and betaine. Furthermore, mmachc mutants bred to express rod and/or cone fluorescent reporters, manifested a retinopathy and thin optic nerves (ON). Expression analysis using whole eye mRNA revealed the dysregulation of genes involved in phototransduction and cholesterol metabolism. Zebrafish with mmachc deficiency recapitulate the several of the phenotypic and biochemical features of the human disorder, including ocular pathology, and show a response to established treatments.

Feline irradiated diet-induced demyelination; a model of the neuropathology of sub-acute combined degeneration?

Irradiation of food at 50–55 kGy results in a profound, chronic demyelinating-remyelinating disease of the entire central nervous system (CNS) in cats, named Feline Irradiated Diet-Induced Demyelination (FIDID). This study examines the early stages of demyelination and long-term consequences of demyelination and remyelination on axon survival or loss. Myelin vacuolation is the primary defect leading to myelin breakdown, demyelination then prompt remyelination in the spinal cord and brain. There is no evidence of oligodendrocyte death. The spinal cord dorsal column is initially spared yet eventually becomes severely demyelinated with subsequent loss of axons in the core and then surface of the fasciculus gracilis. However remyelination of the sub-pial axons in the dorsal column results in their protection. While there was a lack of biochemical evidence of Vitamin B12 deficiency, the pathological similarities of FIDID with sub-acute combined degeneration (SCD) led us to explore treatment with Vitamin B12. Treatment led to recovery or improvement in some cats and neurologic relapse on cessation of B12 therapy. While the reason that irradiated food is myelinotoxic in the cat remains unresolved, nonetheless the neuropathological changes match exactly what is seen in SCD and its models and provide an ideal model to study the cellular and molecular basis of remyelination.

Parenteral hydroxocobalamin dose intensification in five patients with different types of early onset intracellular cobalamin defects: Clinical and biochemical responses

Intracellular cobalamin metabolism (ICM) defects can be present as autosomal recessive or X-linked disorders. Parenteral hydroxocobalamin (P-OHCbl) is the mainstay of therapy, but the optimal dose has not been determined. Despite early treatment, long-term complications may develop. We have analyzed the biochemical and clinical responses in five patients with early onset of different types of ICM defects (cblC: patients 1-3; cblA: patient 4; cblX: patient 5) following daily P-OHCbl dose intensification (DI). In patient 4, P-OHCbl was started at age 10 years and in patient 5 at age 5 years. OHCbl was formulated at either, 5, 25, or 50 mg/mL. P-OHCbl was intravenously or subcutaneously (SQ) delivered, subsequently by placement of a SQ injection port except in patient 4. In all patients, homocysteine and methylmalonic acid levels, demonstrated an excellent response to various P-OHCbl doses. After age 36 months, patients 1-3 had a close to normal neurological examination with lower range developmental quotient. In patient 3, moderate visual impairment was present. Patient 4, at age 10 years, had normal renal, visual and cognitive function. In cblX patient 5, epilepsy was better controlled. In conclusion, P-OHCbl-DI caused an excellent control of metabolites in all patients. In the three cblC patients, comparison with patients, usually harboring identical genotype and similar metabolic profile, was suggestive of a positive effect, in favor of clinical efficacy. With P-OHCbl-DI, CblA patient has been placed into a lower risk to develop renal and optic impairment. In cblX patient, lower P-OHCbl doses were administrated to improve tolerability.

Isolated subacute combined degeneration in late-onset cobalamin C deficiency in children: Two case reports and literature review

RATIONALE

Subacute combined degeneration (SCD) is a disease caused by decreased vitamin B12 intake or metabolic disorders. It is more common in the elderly and rarely seen in children. Here, we report 2 pediatric cases of SCD in late-onset cobalamin C (CblC) deficiency.

PATIENT CONCERNS

The patients complained of unsteady gait. Their physical examination showed sensory ataxia. Magnetic resonance imaging showed classic manifestations of SCD. The serum vitamin B12 level was normal, but urine methylmalonic acid and serum homocysteine levels were high.

DIAGNOSIS

The pathogenic gene was confirmed as MMACHC. The 2 patients each had 2 pathogenic mutations C.482 G>A and C.271dupA and C.365A>T and C.609G>A in this gene. They were diagnosed with combined methylmalonic acidemia and homocysteinemia-CblC subtype.

INTERVENTIONS

The patients were treated with methylcobalamin 500 μg intravenous injection daily after being admitted. After the diagnosis, levocarnitine, betaine, and vitamin B12 were added to the treatment.

OUTCOMES

Twelve days after treatment, the boy could walk normally, and his tendon reflex and sense of position returned to normal. The abnormal gait seemed to have become permanent in the girl and she walked with her legs raised higher than normal.

LESSONS

To the best of our knowledge, this is the first report of 2 cases of isolated SCD in children with late-onset CblC disorder. Doctors should consider that SCD could be an isolated symptom of CblC disorder. The earlier the treatment, the lower the likelihood of sequelae.

[Kidney disease in cobalamin C deficiency]

Cobalamin C deficiency (cblC) is the most common inborn error of vitamin B₁₂ metabolism. This autosomal recessive disease is due to mutations in MMACHC gene, encoding a cyanocobalamin decyanase. It leads to hyperhomocysteinemia associated with hypomethioninemia and methylmalonic aciduria. Two distinct phenotypes have been described : early-onset forms occur before the age of one year and are characterized by a severe multisystem disease associating failure to thrive to neurological and ophthalmological manifestations. They are opposed to late-onset forms, less severe and heterogeneous. CblC deficiency-associated kidney lesions remain poorly defined. Thirty-eight cases have been described. Age at initial presentation varied from a few days to 28 years. Most of the patients presented renal thrombotic microangiopathy (TMA) associated with acute renal failure, and 21 patients presented typical lesions of renal thrombotic microangiopathy on kidney biopsy. Prognosis was poor, leading to death in the absence of treatment, and related to the severity of renal lesions in the early-onset forms. Late-onset disease had better prognosis and most of patients were weaned off dialysis after treatment initiation. We suggest that all the patients with renal TMA be screened for cobalamin metabolism disorder, regardless of age and even in the absence of neurological symptoms, to rapidly initiate the appropriate treatment.

Renal thrombotic microangiopathy and pulmonary arterial hypertension in a patient with late-onset cobalamin C deficiency

Cobalamin C (cblC) deficiency is the most commonly inherited inborn error of vitamin B12 metabolism. It is characterized by multisystem involvement with severe neurological, hematological, renal and cardiopulmonary manifestations. Disease is most commonly diagnosed early in the first decade of life. We report a case of a 20-year-old woman who developed severe pulmonary arterial hypertension while under nephrologic follow-up for chronic kidney disease. She had initially presented at 14 years of age with visual disturbance and acute renal failure and been diagnosed with thrombotic thrombocytopenic purpura on the basis of kidney biopsy findings of thrombotic microangiopathy and compatible ADAMTS13 (a disentegrin and metalloproteinase with a thrombospondin type 1 motif member 13). When cblC deficiency was eventually diagnosed, remarkable improvement in cardiopulmonary function was evident upon initiation of treatment. This case highlights the importance of a timely diagnosis and initiation of treatment for cblC deficiency. Clinical diagnosis may be challenged by asynchronous organ symptom presentation and by misleading laboratory tests, in this case: an initial low ADAMTS13. A simple test of plasma homocysteine level should be encouraged in cases of thrombotic microangiopathy and/or pulmonary artery hypertension.

Guidelines for diagnosis and management of the cobalamin-related remethylation disorders cblC, cblD, cblE, cblF, cblG, cblJ and MTHFR deficiency

BACKGROUND

Remethylation defects are rare inherited disorders in which impaired remethylation of homocysteine to methionine leads to accumulation of homocysteine and perturbation of numerous methylation reactions.

OBJECTIVE

To summarise clinical and biochemical characteristics of these severe disorders and to provide guidelines on diagnosis and management.

DATA SOURCES

Review, evaluation and discussion of the medical literature (Medline, Cochrane databases) by a panel of experts on these rare diseases following the GRADE approach.

KEY RECOMMENDATIONS

We strongly recommend measuring plasma total homocysteine in any patient presenting with the combination of neurological and/or visual and/or haematological symptoms, subacute spinal cord degeneration, atypical haemolytic uraemic syndrome or unexplained vascular thrombosis. We strongly recommend to initiate treatment with parenteral hydroxocobalamin without delay in any suspected remethylation disorder; it significantly improves survival and incidence of severe complications. We strongly recommend betaine treatment in individuals with MTHFR deficiency; it improves the outcome and prevents disease when given early.

A critical reappraisal of dietary practices in methylmalonic acidemia raises concerns about the safety of medical foods. Part 2: cobalamin C deficiency

PURPOSE

Cobalamin C (cblC) deficiency impairs the biosynthesis of adenosyl- and methylcobalamin resulting in methylmalonic acidemia combined with hyperhomocysteinemia and hypomethioninemia. However, some patients with cblC deficiency are treated with medical foods, devoid of methionine and high in leucine content, that are formulated for patients with isolated propionate oxidative defects. We examined the effects of imbalanced branched-chain amino acid intake on growth outcomes in cblC patients.

METHODS

Dietary intake was correlated with biochemical, anthropometric, body composition measurements and other disease parameters in a cohort of 28 early-onset cblC patients.

RESULTS

Protein restricted diets were followed by 21% of the patients, while 32% received medical foods. Patients on protein-restricted diets had lower height-for-age Z-score (P=0.034), while patients consuming medical foods had lower head-circumference Z-scores (P=0.037), plasma methionine concentrations (P=0.001) and predicted methionine influx through the blood brain barrier Z-score (−1.29 vs. −0.0617, P=0.007). The combination of age of diagnosis, a history of seizures and the leucine/valine dietary intake ratio best predicted head circumference Z-score based on multiple regression modeling (R²= 0.945).

CONCLUSIONS

Patients with cblC deficiency treated with medical foods designed for isolated methylmalonic acidemia are at risk for iatrogenic methionine deficiency that could adversely affect brain growth and development.

TRIAL REGISTRATION

This clinical study is registered in www.clinicaltrials.gov with the ID: NCT00078078. Study URL: http://clinicaltrials.gov/ct2/show/NCT00078078

Ocular disease in the cobalamin C defect: a review of the literature and a suggested framework for clinical surveillance

The association between combined methylmalonic acidemia and homocystinuria of cblC type (cobalamin C defect, cblC) and ocular disease is now well recognized, and is a significant component of morbidity and disability associated with the condition. In this review, through collation of historically reported cases of early- and late-onset cblC and previously unreported cases, we have attempted to characterize the epidemiology, clinical features, and pathomechanisms of individual ocular features of cblC. These data suggest that maculopathy and nystagmus with abnormal vision are extremely common and affect the majority of children with early-onset cblC, usually before school age; strabismus and optic atrophy are also seen at relatively high frequency. The timing of progression of macular disease may coincide with a critical period of postnatal foveal development. Maculopathy and retinal disease may be subclinical and show only partial correlation with the extent of visual deficits, and visual deterioration may be relentlessly progressive in spite of aggressive treatment of biochemical abnormalities. In later-onset forms of the disease, visual loss and ocular complications appear to be infrequent. Finally, we discuss investigational strategies in diagnosing and characterizing eye disease in individuals with cblC, explore possible therapeutic avenues that may attenuate progression and severity of eye disease, and propose a clinical surveillance guideline for monitoring progression of ocular disease in children and adults with cblC.

Cobalamin C Disease Missed by Newborn Screening in a Patient with Low Carnitine Level

Cobalamin C (CblC) disease is the most common inherited disorder of intracellular cobalamin metabolism. It is a multisystemic disorder mainly affecting the eye and brain and characterized biochemically by methylmalonic aciduria, low methionine level, and homocystinuria. We report a patient found to have CblC disease who initially presented with low carnitine and normal propionylcarnitine (C3) levels on newborn screen. Newborn screening likely failed to detect CblC in this patient because of both his low carnitine level and the presence of a mild phenotype.

A treatable metabolic cause of encephalopathy: cobalamin C deficiency in an 8-year-old male

Neurologic regression in a previously healthy child may be caused by metabolic or neurodegenerative disorders, many of which have no definitive treatment. We report a case of a previously healthy 8-year-old boy who presented with a month-long history of waxing and waning encephalopathy and acute regression, followed by seizures. Evaluation for a metabolic disorder revealed methylmalonic acidemia and hyperhomocysteinemia of the cobalamin C type due to a single, presumed homozygous pathogenic c.394 C>T mutation in the MMACHC gene. With the appropriate diet restrictions and vitamin replacement, he improved significantly and returned to his premorbid level of behavior. This case illustrates an unusual presentation of a treatable metabolic disorder and highlights the need to consider cobalamin defects in the differential diagnosis of healthy children with neurologic regression.

Clinical presentation and outcome in a series of 88 patients with the cblC defect

The cblC defect is the most common inborn error of vitamin B12 metabolism. Despite therapeutic measures, the long-term outcome is often unsatisfactory. This retrospective multicentre study evaluates clinical, biochemical and genetic findings in 88 cblC patients. The questionnaire designed for the study evaluates clinical and biochemical features at both initial presentation and during follow up. Also the development of severity scores allows investigation of individual disease load, statistical evaluation of parameters between the different age of presentation groups, as well as a search for correlations between clinical endpoints and potential modifying factors.

RESULTS

No major differences were found between neonatal and early onset patients so that these groups were combined as an infantile-onset group representing 88 % of all cases. Hypotonia, lethargy, feeding problems and developmental delay were predominant in this group, while late-onset patients frequently presented with psychiatric/behaviour problems and myelopathy. Plasma total homocysteine was higher and methionine lower in infantile-onset patients. Plasma methionine levels correlated with "overall impression" as judged by treating physicians. Physician's impression of patient's well-being correlated with assessed disease load. We confirmed the association between homozygosity for the c.271dupA mutation and infantile-onset but not between homozygosity for c.394C>T and late-onset. Patients were treated with parenteral hydroxocobalamin, betaine, folate/folinic acid and carnitine resulting in improvement of biochemical abnormalities, non-neurological signs and mortality. However the long-term neurological and ophthalmological outcome is not significantly influenced. In summary the survey points to the need for prospective studies in a large cohort using agreed treatment modalities and monitoring criteria.

Neurologic and neurodevelopmental phenotypes in young children with early-treated combined methylmalonic acidemia and homocystinuria, cobalamin C type

Abnormal neurodevelopment has been widely reported in combined methylmalonic aciduria (MMA) and homocystinuria, cblC type (cblC disease), but neurodevelopmental phenotypes in cblC have not previously been systematically studied. We sought to further characterize developmental neurology in children with molecularly-confirmed cblC. Thirteen children at our center with cblC, born since implementation of expanded newborn screening in New York State, undertook standard-of-care evaluations with a pediatric neurologist and pediatric ophthalmologist. At most recent follow-up (mean age 50 months, range 9-84 months), of twelve children with early-onset cblC, three (25%) had a history of clinical seizures and two (17%) meet criteria for microcephaly. A majority of children had hypotonia and nystagmus. Twelve out of thirteen (92%) underwent neurodevelopmental evaluation (mean age 41 months; range 9-76 months), each child tested with standardized parental interviews and, where possible, age- and disability-appropriate neuropsychological batteries. All patients showed evidence of developmental delay with the exception of one patient with a genotype predictive of attenuated disease and near-normal biochemical parameters. Neurodevelopmental deficits were noted most prominently in motor skills, with relative preservation of socialization and communication skills. Nine children with early-onset cblC underwent magnetic resonance imaging and spectroscopy (MRI/MRS) at mean age of 47 months (range 6-81 months); common abnormalities included callosal thinning, craniocaudally short pons, and increased T2 FLAIR signal in periventricular and periatrial white matter. Our study further characterizes variable neurodevelopmental phenotypes in treated cblC, and provides insights into the etiopathogenesis of disordered neurodevelopment frequently encountered in cblC. Plasma homocysteine and MMA, routinely measured at clinical follow-up, may be poor predictors for neurodevelopmental outcomes. Additional data from large, prospective, multi-center natural history studies are required to more accurately define the role of these metabolites and others, as well as that of other genetic and environmental factors in the etiopathogenesis of the neurologic components of this disorder.

Combined methylmalonic acidemia and homocystinuria, cblC type. I. Clinical presentations, diagnosis and management

Combined methylmalonic acidemia and homocystinuria, cblC type, is an inborn error of intracellular cobalamin metabolism with a wide spectrum of clinical manifestations that is stated to be the most common inherited disorder of cobalamin metabolism. This metabolic disease is caused by mutations in the MMACHC gene and results in impaired intracellular synthesis of adenosylcobalamin and methylcobalamin, cofactors for the methylmalonyl-CoA mutase and methionine synthase enzymes. Elevated methylmalonic acid and homocysteine with decreased methionine production are the biochemical hallmarks of this disorder. Awareness of the diverse clinical presentations associated with cblC disease is necessary to provide a timely diagnosis, to guide management of affected individuals and to establish a framework for the future treatment of individuals detected through expanded newborn screening. This article reviews the biochemistry, clinical presentations, genotype-phenotype correlations, diagnosis and management of cblC disease.

Maternal micronutrients (folic acid and vitamin B(12)) and omega 3 fatty acids: implications for neurodevelopmental risk in the rat offspring

Altered maternal micronutrients (folic acid, vitamin B(12)) are suggested to be at the heart of intra-uterine programming of adult diseases. We have recently described interactions of folic acid, vitamin B(12) and docosahexaenoic acid in one carbon metabolism that is considered to play a key role in regulation oxidative stress and chromatin methylation. However its impact on fetal oxidative stress and brain fatty acid levels has been relatively unexplored. The present study examined the effect of imbalance in maternal micronutrients (folic acid and vitamin B(12)) and maternal omega 3 fatty acid supplementation on oxidative stress parameters and brain fatty acids and in the offspring at birth. Pregnant female rats were divided into six groups at two levels of folic acid both in the presence and absence of vitamin B(12). Both the vitamin B(12) deficient groups were supplemented with omega 3 fatty acid. Oxidative stress marker (malondialdehyde) and polyunsaturated fatty acid profiles in plasma and brain were analyzed in dam and offspring at d20. Our results for the first time indicate that imbalance in maternal micronutrients (excess maternal folic acid supplementation on a B(12) deficient diet) increases (p<0.01) oxidative stress in both mother and pups. This increased maternal oxidative stress resulted in lower (p<0.01) fetal brain DHA levels. Omega 3 fatty acid supplementation was able to restore (p<0.05) the levels of brain DHA in both the vitamin B(12) deficient groups. Our data has implications for implications for neurodevelopmental disorders since micronutrients and DHA are important modulators for neural functioning.

Combined methylmalonic acidemia and homocystinuria, cblC type. II. Complications, pathophysiology, and outcomes

Combined methylmalonic acidemia and homocystinuria, cblC type, is stated to be the most common inborn error of intracellular cobalamin metabolism. The disorder can display a wide spectrum of clinical manifestations, spanning the prenatal period through late adulthood. While increased homocysteine concentrations and impaired methyl group metabolism may contribute to disease-related complications, the characteristic macular and retinal degeneration seen in many affected patients appears to be unique to cblC disease. The early detection of cblC disease by newborn screening mandates a careful assessment of therapeutic approaches and provides a new opportunity to improve the outcome of affected patients. The following article reviews the current knowledge on the complications, pathophysiology, and outcome of cblC disease in an effort to better guide clinical practice and future therapeutic trials.

Effect of maternal micronutrients (folic acid, vitamin B12) and omega 3 fatty acids on liver fatty acid desaturases and transport proteins in Wistar rats

A disturbed fatty acid metabolism increases the risk of adult non-communicable diseases. This study examines the effect of maternal micronutrients on the fatty acid composition, desaturase activity, mRNA levels of fatty acid desaturases and transport proteins in the liver. Pregnant female rats were divided into 6 groups at 2 levels of folic acid both in the presence and absence of vitamin B(12). The vitamin B(12) deficient groups were supplemented with omega 3 fatty acid. An imbalance of maternal micronutrients reduces liver docosahexaenoic acid, increases Δ5 desaturase activity but decreases mRNA levels, decreases Δ6 desaturase activity but not mRNA levels as compared to control. mRNA level of Δ5 desaturase reverts back to the levels of the control group as a result of omega 3 fatty acid supplementation. Our data for the first time indicates that maternal micronutrients differentially alter the activity and expression of fatty acid desaturases in the liver.

Maternal supplementation of omega 3 fatty acids to micronutrient-imbalanced diet improves lactation in rat

The present study aims to examine the effect of maternal supplementation of omega 3 fatty acids to a micronutrient (folic acid and vitamin B(12))-imbalanced diet on gastric milk volume and long-chain polyunsaturated fatty acid composition. Pregnant female rats were divided into 6 groups at 2 levels of folic acid in both the presence and absence of vitamin B(12). Both vitamin B(12)-deficient groups were supplemented with omega 3 fatty acid. Gastric milk volume and long-chain polyunsaturated fatty acids were analyzed. Our results for the first time indicate that imbalance in maternal micronutrients reduces gastric milk volume and milk docosahexaenoic acid levels (P < .01 for both) as compared with control. Supplementation with omega 3 fatty acids to this diet imbalanced in micronutrients increases (P < .01) milk docosahexaenoic acid level as compared with control. Imbalance in maternal micronutrients during pregnancy can alter milk fatty acid composition, which may ultimately affect infant growth and development.

Combined methylmalonic aciduria and homocystinuria cblC type of a Taiwanese infant with c.609G>A and C.567dupT mutations in the MMACHC gene

Combined methylmalonic aciduria and homocystinuria, cobalamin (cbl)C type (cblC disease), the most common inborn error of vitamin B(12), is a rare disorder of intracellular cbl metabolism because of mutations in the MMACHC gene located in chromosome region 1p34.1. It has become possible to establish phenotype-genotype correlations and to observe ethnicity-related trends. This article provides detailed clinical manifestations and outcomes of a Taiwanese infant boy with early-onset cblC disease, heterozygous for c.609G>A and c.567dupT mutations, although there is limited information about cases with c.609G>A or c.567dupT mutation in the literature. He had no significant clinical abnormality during his neonatal period, whereas elevated C3 level was noted at newborn screening. He presented later with life-threatening manifestations and failure to thrive, which resolved through our treatment, although delayed development was still noted at 6 months of age. To date, all reported cblC patients with the c.609G>A mutation have been East Asians. Therefore, we suggest that c.609G>A should be included in the initial mutation screening tests for a cblC patient in East Asian populations.

Cobalamin C defect: natural history, pathophysiology, and treatment

Cobalamin C (Cbl-C) defect is the most common inborn cobalamin metabolism error; it causes impaired conversion of dietary vitamin B12 into its two metabolically active forms, methylcobalamin and adenosylcobalamin. Cbl-C defect causes the accumulation of methylmalonic acid and homocysteine and decreased methionine synthesis. The gene responsible for the Cbl-C defect has been recently identified, and more than 40 mutations have been reported. MMACHC gene is located on chromosome 1p and catalyzes the reductive decyanation of CNCbl. Cbl-C patients present with a heterogeneous clinical picture and, based on their age at onset, can be categorized into two distinct clinical forms. Early-onset patients, presenting symptoms within the first year, show a multisystem disease with severe neurological, ocular, haematological, renal, gastrointestinal, cardiac, and pulmonary manifestations. Late-onset patients present a milder clinical phenotype with acute or slowly progressive neurological symptoms and behavioral disturbances. To improve clinical course and metabolic abnormalities, treatment of Cbl-C defect usually consists of a combined approach that utilizes vitamin B12 to increase intracellular cobalamin and to maximize deficient enzyme activities, betaine to provide a substrate for the conversion of homocysteine into methionine through betaine-homocysteine methyltransferase, and folic acid to enhance remethylation pathway. No proven efficacy has been demonstrated for carnitine and dietary protein restriction. Despite these measures, the long-term follow-up is unsatisfactory especially in patients with early onset, with frequent progression of neurological and ocular impairment. The unfavorable outcome suggests that better understanding of the pathophysiology of the disease is needed to improve treatment protocols and to develop new therapeutic approaches.

Clinical, biochemical, and molecular analysis of combined methylmalonic acidemia and hyperhomocysteinemia (cblC type) in China

The most common inborn error of cobalamin (cbl) metabolism in China is the cblC type characterized by combined methylmalonic acidemia and hyperhomocysteinemia. The clinical presentation is relatively nonspecific, such as feeding difficulty, recurrent vomiting, hypotonia, lethargy, seizures, progressive developmental delay, and mental retardation, together with anemia and metabolic acidosis. More specific biochemical findings include high levels of propionylcarnitine (C3), free carnitine (C3/C0), and acetylcarnitine (C3/C2) measured by tandem mass spectrometry (MS/MS), elevation of methylmalonic acid (MMA) measured by gas chromatography-mass spectrometry (GC-MS), and increased total homocysteine with normal or decreased methionine. We report on 50 Chinese patients with combined methylmalonic acidemia and hyperhomocysteinemia. Forty-six belonged to the cblC complementation group. Mutation analysis of the MMACHC gene was performed to characterize the mutational spectrum of cblC deficiency, and 17 different mutations were found. Most were clustered in exons 3 and 4, accounting for 91.3% of all mutant alleles. Two mutations were novel, namely, c.315 C>G (p.Y105X) and c.470 G>C(p.W157S). In terms of genotype-phenotype correlation, the c.609 G>A mutation was associated with early-onset disease when homozygous. Unlike previous reports from other populations, c.609 G>A (p.W203X) was the most frequent cblC mutation detected in our study of Chinese patients, affecting 51 of 92 MMACHC alleles (55.4%). The high prevalence of this nonsense mutation could have potential therapeutic significance for Chinese cblC patients. Besides traditional approaches consisting of hydroxocobalamin injections, carnitine, betaine, and protein restriction, novel drugs that target premature termination codons may have a role in the future.

Genetic and cellular studies of oxidative stress in methylmalonic aciduria (MMA) cobalamin deficiency type C (cblC) with homocystinuria (MMACHC)

Methylmalonic aciduria (MMA) cobalamin deficiency type C (cblC) with homocystinuria (MMACHC) is the most frequent genetic disorder of vitamin B(12) metabolism. The aim of this work was to identify the mutational spectrum in a cohort of cblC-affected patients and the analysis of the cellular oxidative stress and apoptosis processes, in the presence or absence of vitamin B(12). The mutational spectrum includes nine previously described mutations: c.3G>A (p.M1L), c.217C>T (p.R73X), c.271dupA (p.R91KfsX14), c.331C>T (p.R111X), c.394C>T (p.R132X), c.457C>T (p.R153X), c.481C>T (p.R161X), c.565C>A (p.R189S), and c.615C>G (p.Y205X), and two novel changes, c.90G>A (p.W30X) and c.81+2T>G (IVS1+2T>G). The most frequent change was the known c.271dupA mutation, which accounts for 85% of the mutant alleles characterized in this cohort of patients. Owing to its high frequency, a real-time PCR and subsequent high-resolution melting (HRM) analysis for this mutation has been established for diagnostic purposes. All cell lines studied presented a significant increase of intracellular reactive oxygen species (ROS) content, and also a high rate of apoptosis, suggesting that elevated ROS levels might induce apoptosis in cblC patients. In addition, ROS levels decreased in hydroxocobalamin-incubated cells, indicating that cobalamin might either directly or indirectly act as a scavenger of ROS. ROS production might be considered as a phenotypic modifier in cblC patients, and cobalamin supplementation or additional antioxidant drugs might suppress apoptosis and prevent cellular damage in these patients.

Hydroxocobalamin dose escalation improves metabolic control in cblC

Cobalamin C (cblC), a combined form of methylmalonic acidaemia and hyperhomocysteinaemia, is recognized as the most frequent inborn error of intracellular cobalamin metabolism. This condition can be detected by expanded newborn screening and can have an acute neonatal presentation that is life-threatening if not suspected and promptly treated. Intramuscular (IM) hydroxocobalamin (OHCbl) is the main treatment for patients with cblC, but formal dosing guidelines do not exist. A clinical improvement and a decrease of plasma methylmalonic acid (MMA) and total homocysteine (tHcy) levels, and an increase in methionine are typically observed after its initiation. It is well recognized that despite treatment, long-term complications such as developmental delay and progressive visual loss, may still develop. We describe the biochemical response of a 13-year-old boy with worsening metabolic parameters despite strict adherence to a conventional treatment regimen. We progressively increased the OHCbl dose from 1 to 20 mg IM per day and observed a dose-dependent response with an 80% reduction of plasma MMA (25 to 5.14 micromol/L; normal range <0.27 micromol/L), a 55% reduction of tHcy (112 to 50 micromol/L; normal range: 0-13 micromol/L) and a greater than twofold increase in methionine (17 to 36 micromol/L; normal range: 7-47 micromol/L). This suggests that higher OHCbl doses might be required to achieve an optimal biochemical response in cblC patients, but it is unknown whether it may slow or eliminate other complications. Future clinical trials to determine the benefits of higher-dose OHCbl therapy in patients with cblC and other disorders of intracellular cobalamin metabolism should be planned.

Spectrum of mutations in MMACHC, allelic expression, and evidence for genotype-phenotype correlations

Methylmalonic aciduria and homocystinuria, cblC type, is a rare disorder of intracellular vitamin B(12) (cobalamin [Cbl]) metabolism caused by mutations in the MMACHC gene. MMACHC was sequenced from the gDNA of 118 cblC individuals. Eleven novel mutations were identified, as well as 23 mutations that were observed previously. Six sequence variants capture haplotype diversity in individuals across the MMACHC interval. Genotype-phenotype correlations of common mutations were apparent; individuals with c.394C>T tend to present with late-onset disease whereas patients with c.331C>T and c.271dupA tend to present in infancy. Other missense variants were also associated with late- or early-onset disease. Allelic expression analysis was carried out on human cblC fibroblasts compound heterozygous for different combinations of mutations including c.271dupA, c.331C>T, c.394C>T, and c.482G>A. The early-onset c.271dupA mutation was consistently underexpressed when compared to control alleles and the late-onset c.394C>T and c.482G>A mutations. The early-onset c.331C>T mutation was also underexpressed when compared to control alleles and the c.394C>T mutation. Levels of MMACHC mRNA transcript in cell lines homozygous for c.271dupA, c.331C>T, and c.394C>T were assessed using quantitative real-time RT-PCR. Cell lines homozygous for the late onset c.394C>T mutation had significantly higher levels of transcript when compared to cell lines homozygous for the early-onset mutations. Differential or preferential MMACHC transcript levels may provide a clue as to why individuals carrying c.394C>T generally present later in life.

Prevention of brain disease from severe 5,10-methylenetetrahydrofolate reductase deficiency

Over a four-year period, we collected clinical and biochemical data from five Amish children who were homozygous for missense mutations in 5,10-methylenetetrahydrofolate reductase (MTHFR c.1129C>T). The four oldest patients had irreversible brain damage prior to diagnosis. The youngest child, diagnosed and started on betaine therapy as a newborn, is healthy at her present age of three years. We compared biochemical data among four groups: 16 control subjects, eight heterozygous parents, and five affected children (for the latter group, both before and during treatment with betaine anhydrous). Plasma amino acid concentrations were used to estimate changes in cerebral methionine uptake resulting from betaine therapy. In all affected children, treatment with betaine (534+/-222 mg/kg/day) increased plasma S-adenosylmethionine, improved markers of tissue methyltransferase activity, and resulted in a threefold increase of calculated brain methionine uptake. Betaine therapy did not normalize plasma total homocysteine, nor did it correct cerebral 5-methyltetrahydrofolate deficiency. We conclude that when the 5-methyltetrahydrofolate content of brain tissue is low, dietary betaine sufficient to increase brain methionine uptake may compensate for impaired cerebral methionine recycling. To effectively support the metabolic requirements of rapid brain growth, a large dose of betaine should be started early in life.