Metabolites Methylmalonic Acid Research Articles

Aging-Associated Metabolite Methylmalonic Acid Increases Susceptibility to Pulmonary Fibrosis

Aging-Associated Metabolite Methylmalonic Acid Increases Susceptibility to Pulmonary Fibrosis

Sexual dimorphism in mitochondrial dysfunction and diabetes mellitus: evidence from a population-based cohort study

BackgroundPathophysiological mechanisms underlying sex-based differences in diabetes remain poorly understood. Mitochondrial metabolite methylmalonic acid (MMA) accumulation reflects mitochondrial dysfunction which is involved in sex-specific pathophysiological responses biologically. We aimed to investigate the sex-specific associations between mortality risk and MMA in adults with the presence or absence of type 2 diabetes.MethodsThis cohort study included 24,164 adults (12,123 females and 12,041 males) from the NHANES study during 1999–2014. Both sexes were separately categorized as those with no diabetes, prediabetes, undiagnosed diabetes, and diagnosed diabetes. Circulating MMA level was measured at baseline by mass-spectrometric detection. Mortality status was ascertained from baseline until December 31, 2015.ResultsDuring a median follow-up of 11.1 years, 3375 deaths were documented. Males had a particularly higher mortality than females in adults with diagnosed diabetes compared to differences in those with no diabetes, prediabetes and undiagnosed diabetes (sex differences in mortality rate per 1000 person-years across diabetic status: 0.62, 1.44, 5.78, and 9.77, p < 0.001). Notably, the sex-specific difference in associations between MMA and mortality was significant only in adults with diagnosed diabetes (p for interaction = 0.028), not in adults with no diabetes and prediabetes. Adjusted HRs (95%CIs) per doubling of MMA for all-cause mortality were 1.19 (1.04–1.37) in females with diagnosed diabetes versus 1.58 (1.36–1.86) in male counterparts. In addition, MMA levels had an insignificant or weak correlation with sex hormone profiles at baseline, regardless of diabetes status and sex.ConclusionsSex difference in mortality risk was especially significant in diagnosed type 2 diabetes. Increasing equivalent exposure to mitochondrial metabolite MMA was associated with a greater excess risk of future mortality in males with diabetes than in females.

Abnormal chondrocyte development in a zebrafish model of cblC syndrome restored by an MMACHC cobalamin binding mutant

Variants in the MMACHC gene cause combined methylmalonic acidemia and homocystinuria cblC type, the most common inborn error of intracellular cobalamin (vitamin B12) metabolism. cblC is associated with neurodevelopmental, hematological, ocular, and biochemical abnormalities. In a subset of patients, mild craniofacial dysmorphia has also been described. Mouse models of Mmachc deletion are embryonic lethal but cause severe craniofacial phenotypes such as facial clefts. MMACHC encodes an enzyme required for cobalamin processing and variants in this gene result in the accumulation of two metabolites: methylmalonic acid (MMA) and homocysteine (HC). Interestingly, other inborn errors of cobalamin metabolism, such as cblX syndrome, are associated with mild facial phenotypes. However, the presence and severity of MMA and HC accumulation in cblX syndrome is not consistent with the presence or absence of facial phenotypes. Thus, the mechanisms by which mutations in MMACHC cause craniofacial defects are yet to be completely elucidated. Here we have characterized the craniofacial phenotypes in a zebrafish model of cblC (hg13) and performed restoration experiments with either a wildtype or a cobalamin binding deficient MMACHC protein. Homozygous mutants did not display gross morphological defects in facial development but did have abnormal chondrocyte nuclear organization and an increase in the average number of neighboring cell contacts, both phenotypes were fully penetrant. Abnormal chondrocyte nuclear organization was not associated with defects in the localization of neural crest specific markers, sox10 (RFP transgene) or barx1. Both nuclear angles and the number of neighboring cell contacts were fully restored by wildtype MMACHC and a cobalamin binding deficient variant of the MMACHC protein. Collectively, these data suggest that mutation of MMACHC causes mild to moderate craniofacial phenotypes that are independent of cobalamin binding.

Association of Vitamin B&lt;sub&gt;12&lt;/sub&gt; Status with Biochemical Parameters among the Adult Population (30 - 50 Years) of Vallabh Vidyanagar, Anand, Gujarat

Vitamin B12 deficiency is known to be very common amongst the vegan population and can cause hyperhomocysteinemia due to various hematologic and neuropsychiatric disorders. Vitamin B12 deficiency is a global epidemic caused by malabsorption and inadequate consumption. Vitamin B12 deficiency has the greatest impact on the blood and nervous system. Elevated Methylmalonic Acid (MMA) and/or total homocysteine levels are sensitive indications of vitamin B12 deficiency and have been linked to clinical problems. Hematological parameters like erythrocyte count, hemoglobin concentration or hematocrit, Mean Cell Volume (MCV), blood values such as plasma B12 and the metabolite MMA are only a few examples. A total of 398 subjects, aged 30-50 years were selected from Vallabh Vidyanagar, Anand, Gujarat. Fourty two percent of the subjects were suffering from vitamin B12 deficiency. The subjects were screened for their vitamin B12 status and several biochemical parameters like homocysteine, iron, hemoglobin, total RBC, PCV, MCV, MCH, MCHC and RDW. Total RBC, MCV, MCH, MCHC levels, and homocysteine concentration of the subjects were found to be significantly (P ? 0.05) associated with the vitamin B12 status of the subjects. A positive and significant (P ? 0.05) relationship was observed between serum vitamin B12 and iron levels (r = 0.127, P ? 0.05) of the subjects. In conclusion, vitamin B12 status was significantly associated with total RBC, MCV, MCH, MCHC levels and homocysteine concentration

Toxic Metabolites and Inborn Errors of Amino Acid Metabolism: What One Informs about the Other.

In inborn errors of metabolism, such as amino acid breakdown disorders, loss of function mutations in metabolic enzymes within the catabolism pathway lead to an accumulation of the catabolic intermediate that is the substrate of the mutated enzyme. In patients of such disorders, dietarily restricting the amino acid(s) to prevent the formation of these catabolic intermediates has a therapeutic or even entirely preventative effect. This demonstrates that the pathology is due to a toxic accumulation of enzyme substrates rather than the loss of downstream products. Here, we provide an overview of amino acid metabolic disorders from the perspective of the ‘toxic metabolites’ themselves, including their mechanism of toxicity and whether they are involved in the pathology of other disease contexts as well. In the research literature, there is often evidence that such metabolites play a contributing role in multiple other nonhereditary (and more common) disease conditions, and these studies can provide important mechanistic insights into understanding the metabolite-induced pathology of the inborn disorder. Furthermore, therapeutic strategies developed for the inborn disorder may be applicable to these nonhereditary disease conditions, as they involve the same toxic metabolite. We provide an in-depth illustration of this cross-informing concept in two metabolic disorders, methylmalonic acidemia and hyperammonemia, where the pathological metabolites methylmalonic acid and ammonia are implicated in other disease contexts, such as aging, neurodegeneration, and cancer, and thus there are opportunities to apply mechanistic or therapeutic insights from one disease context towards the other. Additionally, we expand our scope to other metabolic disorders, such as homocystinuria and nonketotic hyperglycinemia, to propose how these concepts can be applied broadly across different inborn errors of metabolism and various nonhereditary disease conditions.

Central nervous system-targeted adeno-associated virus gene therapy in methylmalonic acidemia

Methylmalonic acidemia (MMA) is a severe metabolic disorder most commonly caused by a mutation in the methylmalonyl-CoA mutase (MMUT) gene. Patients with MMA experience multisystemic disease manifestations and remain at risk for neurological disease progression, even after liver transplantation. Therefore, delivery of MMUT to the central nervous system (CNS) may provide patients with neuroprotection and, perhaps, therapeutic benefits. To specifically target the brain, we developed a neurotropic PHP.eB vector that used a CaMKII neuro-specific promoter to restrict the expression of the MMUT transgene in the neuraxis and delivered the adeno-associated virus (AAV) to mice with MMA. The PHP.eB vector transduced cells in multiple brain regions, including the striatum, and enabled high levels of expression of MMUT in the basal ganglia. Following the CNS-specific correction of MMUT expression, disease-related metabolites methylmalonic acid and 2-methylcitrate were significantly (p < 0.02) decreased in serum of treated MMA mice. Our results show that targeting MMUT expression to the CNS using a neurotropic capsid can decrease the circulating metabolite load in MMA and further highlight the benefit of extrahepatic correction for disorders of organic acid metabolism.

Metabolic ageing drives tumour progression

Gomes et al. show that age-dependent upregulation of levels of the metabolite methylmalonic acid (MMA) in serum from healthy donors can promote tumour progression in mice via SOX4-dependent regulation of cell fate decisions.

Vitamin B12 Status Upon Short-Term Intervention with a Vegan Diet-A Randomized Controlled Trial in Healthy Participants.

Vegans are at an increased risk for certain micronutrient deficiencies, foremost of vitamin B12. Little is known about the short-term effects of dietary change to plant-based nutrition on vitamin B12 metabolism. Systemic biomarkers of vitamin B12 status, namely, serum vitamin B12 and holotranscobalamin, may respond quickly to a reduced intake of vitamin B12. To test this hypothesis, 53 healthy omnivore subjects were randomized to a controlled unsupplemented vegan diet (VD, n = 26) or meat-rich diet (MD, n = 27) for 4 weeks. Vitamin B12 status was examined by measurement of serum vitamin B12, holotranscobalamin (holo-TC), methylmalonic acid (MMA) and total plasma homocysteine (tHcy). Holo-TC decreased significantly in the VD compared to the MD group after four weeks of intervention, whereas metabolites MMA and tHcy were unaffected. Body weight remained stable in both groups. VD intervention led to a significant reduction of cholesterol intake, and adequate profiles of nutrient and micronutrient status. Lower intake of vitamin B12 was observed in VD, which was mirrored by a lower concentration of serum vitamin B12 and reduced holo-TC after 4 weeks. Plasma holo-TC may be a fast-responding biomarker to monitor adequate supply of vitamin B12 in plant-based individuals.

Functional vitamin B12 deficiency in advanced malignancy: implications for the management of neuropathy and neuropathic pain.

Treatment of neuropathic pain and chemotherapy-induced peripheral neuropathy (CIPN) in patients with malignancy is often unsuccessful. Functional vitamin B12 deficiency, defined by elevated levels of the B12-dependent metabolites, methylmalonic acid (MMA), and/or homocysteine, despite normal B12 values, may cause neuropathy and is associated with disorders linked to increased oxidative stress. Since both cancer and neurotoxic antineoplastic agents increase oxidative stress, a role for functional B12 deficiency in CIPN was considered. A retrospective record review of 241 cancer subjects evaluated by the adult palliative care service for B12 deficiency in a university-based cancer center between October 2008 and September 2012 with measurement of B12, MMA, and/or homocysteine levels was performed. B12 values were elevated (>900pg/ml) in 30% and low (≤300pg/ml) in 17% of subjects tested. Elevated MMA (>250nmol/l) and homocysteine (>12.1μmol/l) levels occurred in 38 and 23% of subjects respectively and at least one metabolite was increased in 54% of evaluable subjects. Even when B12 values were ≥1500pg/ml (n=36), increased MMA and homocysteine values occurred in 31 and 23% of subjects, respectively. B12 therapy decreased MMA values in all four subjects studied and improved neurologic findings in the three subjects tested. Functional vitamin B12 deficiency is common in subjects with advanced malignancy. Further studies are needed to determine if this disorder is a risk factor for CIPN and if B12 therapy has a role in the management and/or prevention of neuropathy and neuropathic pain in this population.

Vitamin B12-responsive neuropathies: A case series

Objectives: Neuropathies often accompany vitamin B12 deficiency. Since many neuropathies are linked to oxidative stress and since B12 has both antioxidant and neurotrophic properties, B12 may also be effective treatment in non-deficient subjects. Thus, the characteristics and predictors of B12-responsive neuropathies and their relationship to disorders associated with increased oxidative stress (oxidant risks) were examined.Methods: Retrospective review of 78 subjects with neurological abnormalities treated with B12 and evaluated by the measurement of B12 and the B12-dependent metabolites, methylmalonic acid (MMA), and homocysteine.Results: Sixty-five subjects had neurological improvement (83%), including 35 with other known causes of neuropathy. Only two responders had B12-responsive macrocytosis. Pretherapy B12, MMA, and homocysteine values were normal in 72, 33 and 54% of responders, with all three normal in 23%. Moreover, B12 therapy did not significantly decrease elevated MMA and homocysteine levels in 20 and 37%, respectively, of responders tested but did decrease both metabolites in 75% of evaluable non-responders. At least one oxidant risk was present in 41 of the 46 responders with normal B12 levels (89%). Oral therapy was effective, but parenteral B12 improved responses in four subjects.Discussion: B12-responsive neuropathies are thus (1) common even when confounding disorders are present; (2) dissociated from the presence of hematological abnormalities; (3) dissociated from the presence of B12-responsive metabolical abnormalities; and (4) associated with the presence of oxidant risks when B12 levels are normal. Since no predictors of responses to B12 therapy were identified, empiric trials with parenteral B12 should be considered in appropriate subjects.

Functional cobalamin (vitamin B12) deficiency: role of advanced age and disorders associated with increased oxidative stress.

Functional cobalamin (Cbl; vitamin B12) deficiency (that is, high levels of the Cbl-dependent metabolites, methylmalonic acid (MMA) and homocysteine (HCys), despite normal serum Cbl values) is common in the elderly and is associated with neurocognitive abnormalities, but its cause is unknown. As only reduced Cbls are metabolically active, the possibility that functional Cbl deficiency is associated with disorders having biomarkers indicative of increased oxidative stress (oxidant risks) was considered. A retrospective record review of community-dwelling adults evaluated over a 12-year period for Cbl deficiency in a primary care setting who had serum Cbl values ⩾400 pg/ml (n=170). When no oxidant risks were present, older subjects (⩾70 years) had higher metabolite values than younger individuals (<70 years). MMA values were even higher in the elderly when one oxidant risk was present and in younger subjects when two or more oxidant risks were present. Even at Cbl levels ⩾800 pg/ml, MMA values were increased in 73% of elderly subjects with at least one oxidant risk. HCys values were also higher in both age groups when at least two oxidant risks were present. Cyanocobalamin therapy decreased MMA and HCys values in 86 and 76% of subjects, respectively, with nonresponders more likely to have two or more oxidant risks. Functional Cbl deficiency is associated with disorders marked by increased oxidative stress particularly in the elderly; it occurs even when Cbl levels are high and is not consistently corrected with high-dose cyanocobalamin therapy. Thus, current approaches to recognizing and managing this disorder may be inadequate.

Advanced Age As a Risk Factor for Folate-Induced Cobalamin (Cbl) Deficiency

Abstract 5268 Folate therapy can induce or exacerbate neuro-cognitive changes in patients with clinically significant Cbl deficiency. High serum folate (sFol) values in subjects with low Cbl levels have also been associated with increases in the Cbl-dependent metabolite, methylmalonic acid (MMA) as well as with hematologic, neuro-cognitive and fetal abnormalities, raising concerns about the use of both folate supplements and folate-fortified grains. However, in a more recent study of young adults, MMA values were unaffected by high sFol values. Significantly, advanced age is also linked to increased MMA values even when Cbl values are normal. Thus, a retrospective study was performed of 91 non-diabetic subjects with normal renal function and low-normal Cbl values (201–300 pg/ml) who were evaluated for Cbl deficiency in an ambulatory care setting over a 10 year period to determine if age is a significant determinant of the metabolic interaction of sFol and Cbl when Cbl levels are within the normal reference range. In older individuals (≥60 yrs) with low-normal serum Cbl values, the geometric mean MMA value was significantly higher (401 nmol/l; n=11) when sFol values were elevated (&gt;20 ng/ml) than when sFol values were normal (298 nmol/l; n=35)(p&lt;0.025). In contrast, in younger subjects, mean MMA values were similar in both high and normal sFol groups (302 nmol/l; n=15 vs 270 nmol/l; n=30)(p=0.52). There was no correlation between MMA and sFol when sFol values were within the normal range in either age group (r≤0.07). Finally, when sFol levels were elevated, Cbl therapy significantly decreased MMA values in 8 of 9 younger subjects (89%) and in all 7 older individuals (100%) studied. It is concluded that: 1) MMA values are increased when sFol levels are elevated and Cbl values are low-normal but this effect is age-dependent; 2) the effect of sFol on MMA is not progressive but occurs only at sFol values above the normal range; and 3) Cbl therapy decreases MMA values in almost all subjects regardless of pretreatment sFol values. Since these findings may have clinical significance, caution in the use of folate supplements is advised. Disclosures: No relevant conflicts of interest to declare.

Oxidant Stress as a Cause of Clinically Significant “Functional” Cobalamin (Cbl) Deficiency

Many patients (pts) with Cbl-responsive disorders identified in the ambulatory care setting have reversible neurologic abnormalities associated with increased levels of the Cbl-dependent metabolites, methylmalonic acid (MMA) and homocysteine (HCys), despite normal serum Cbl values. However, no mechanism to explain these findings has been proposed. Since this picture resembles both the CblC mutation (where reduction of CblCo(III) to CblCo(II) is impaired) and nitrous oxide exposure (which inactivates methionine synthase by oxidation of CblCo(I)), a pathophysiologic role for oxidant stress leading to “Functional” Cbl deficiency was considered. Thus, a retrospective review was performed of 39 pts with Cbl-responsive hematologic or neurologic disorders seen during a 14 yr period for the presence of 6 factors associated with increased oxidant stress: advanced age (>69 yrs); diabetes mellitus; cigarette abuse; alcohol abuse; renal insufficiency; and the presence of active inflammatory disorders. Pts were classified as Cbl-Deficient (Group A: serum Cbl <201 pg/ml; N=9); Possibly Cbl-Deficient (Group B: serum Cbl=201–300 pg/ml with MMA >250 nmol/l; N=12); and “Functional” Cbl Deficiency (Group C: serum Cbl >300 pg/ml with MMA >250 nmol/l; N=18). HCys values were increased (>12.1 μmol/l) in 67%, 75% and 50% of evaluable pts in Groups A, B and C respectively. Reversible neurologic abnormalities occurred in 44% of Group A pts, 67% of Group B pts and 100% of Group C pts. In Group C pts, 83% of cases had at least 2 oxidant risk factors. In contrast, only 22% of Group A pts had 1 risk factor and only 11% had 2 risk factors (p<0.002 vs Group C). Similarly, at least 1 oxidant risk factor was present in 67% of Group B pts (p<0.02 vs Group A) but only 17% had 2 risk factors (p<0.001 vs Group C). Moreover, within Group B, only 1 of 4 pts with serum Cbl values of 201–250 pg/ml had 1 oxidant risk factor (25%), while 7 of 8 pts with serum Cbl values of 251–300 pg/ml had at least 1 risk factor (88%)(p<0.03). Finally, when all 207 pts screened for Cbl deficiency during this period who had serum Cbl values >300 pg/ml were reviewed, MMA values were found to be >250 nmol/l in 81 of them (40%). At least 1 oxidant risk factor was present in 77% of the 81 pts with high MMA values but in only 20% of the 126 pts with normal MMA values (p<0.001). HCys levels were also increased in 42 of the 78 pts with high MMA values studied (54%) and Cbl therapy significantly decreased MMA and HCys values in 83% and 85% respectively of evaluable pts in this population. In contrast, only 11% of the 126 pts with normal MMA values had high HCys levels (p<0.001). It is concluded that “Functional” Cbl-deficiency isassociated with disorders known to induce oxidant stress;more commonly encountered as a cause of elevated metabolite levels and neurologic abnormalities than classic Cbl Deficiency; andoften responds to Cbl therapy.Taken together, these data suggest a cumulative effect of oxidant risk factors at higher serum Cbl values leading first to increases in MMA and then to clinically significant neurologic abnormalities. Thus, Cbl inactivation may play a role in the development of neuropathy when high risk individuals experience inflammatory illnesses or are exposed to prooxidant drugs and a possible prophylactic or therapeutic role for reduced Cbl vitamers should be considered.

Laboratory Investigation of Vitamin B12Deficiency

Vitamin B 12 deficiency is not uncommon, particularly in certain patient populations such as elderly, neuropsychiatric, and psychiatric patients. Historically, presentation of vitamin B 12 deficiency was recognized as megaloblastic anemia, which is now rarely seen in Western society. Hematological changes, including macrocytic anemia, are a more well-known symptom, but are not always present or are revealed later in the disease course. However, the advances over the last few decades, from the use of the obsolete Schilling test and total serum vitamin B 12 level to newer methods such as holo-transcobalamin II, the metabolites methylmalonic acid and homocysteine, antibody testing, and gastrin levels, have created a more accurate diagnosis of the disease. Total serum vitamin B 12 level, though sometimes misleading, remains a mainstay of clinical diagnosis. In this work, we will discuss vitamin B 12 deficiency, various diagnostic tests, and an algorithm used in the investigation of vitamin B 12 deficiency.

Serum levels of total homocysteine, homocysteine metabolites and of advanced glycation end-products (AGEs) in patients after renal transplantation.

Hyperhomocysteinemia has been described as an independent risk factor for cardiovascular diseases (CVD) influencing patient outcome. Advanced glycation end-products (AGEs) are involved in the pathogenesis of vascular damage in uremia. This study was undertaken to assess whether high serum levels of total homocysteine (tHcy) with its metabolites methylmalonic acid (MMA), methylcitric acid (MCA) and cystathionine (CYSTA) as well as elevated serum concentrations of the AGEs pentosidine and Nepsilon-carboxymethyllysine (CML) are independent risk factors for CVD, left ventricular hypertrophy (LVH) or hypertension as well as kidney dysfunction in renal transplant recipients (RTR). Serum levels of tHCy, MMA, MCA and CYSTA were measured by a gas chromatographic-mass spectrometric assay, pentosidine by HPLC and CML using an ELISA assay. All measured parameters were significantly higher in RTRs than in healthy subjects (p < 0.0001). The levels of pentosidine and CML as well as of tHcy and its metabolites correlated significantly with each other, but not with those ofMMA and CYSTA. Significant correlations were also found between pentosidine and tHcy, MMA or MCA as well as between CML, MMA and MCA, respectively. Acute or chronic rejection did not influence these values. No significant differences were observed between patients with or without CVD or with hypertension. In RTRs with LVH, only the tHcy levels were significantly higher than in those RTRs without LVH (p = 0.006). Logistic regression analysis revealed an independent influence of tHcy on the presence of LVH. These results may indicate an association between high tHcy values and LVH. Further investigation is needed to determine whether a reduction of tHcy and Hcy metabolites and/or AGE serum concentrations would significantly improve patient outcome after undergoing renal transplantation.

Is low-dose oral cobalamin enough to normalize cobalamin function in older people?

To investigate whether the use of low-dose oral cobalamin (Cbl) supplements by older persons, as frequently found in multivitamin preparations, affects their Cbl serum concentrations and function, determined by measurements of the serum Cbl-related metabolites methylmalonic acid (MMA), homocysteine (HCYS), and methylcitric acid (MCTR). Cross-sectional study. Community. Two hundred forty-two independent, active, community-living, older adult volunteers recruited from community events and activities for seniors. We systematically collected data on vitamin supplement intake, diet, medications, and medical and surgical history. Serum was obtained for Cbl, MMA, HCYS, and MCTR, and creatinine and hematological parameters. Serum levels of Cbl were significantly higher in subjects on oral Cbl supplements (2-37.5 microg/day). Similarly, serum levels of the metabolites MMA, HCYS, and MCTR were also lower in subjects on Cbl supplementation. Intake of low-dose oral supplements of Cbl significantly reduced the odds of low Cbl levels or high MMA. The relationship between Cbl supplement dosage and the biochemical parameters was dose dependent. Oral Cbl (2-37.5 microg/day) intake by community-dwelling healthy older adults is associated with higher serum levels of Cbl and improved or normalized Cbl function, as indicated by lower concentrations of the metabolites MMA, HCYS, and MCTR. Use of low-dose oral Cbl replacement therapy might be sufficient to prevent Cbl deficiency in a large proportion of this population.

Peripheral Neuropathy Due to Cobalamin Deficiency.

Vitamin B12, or cobalamin (Cbl), deficiency can produce a number of neurologic complications, including myelopathy, peripheral neuropathy, optic neuropathy, and dementia. The myelopathy, combined systems disease, is probably the most well known manifestation, and is usually readily recognized. The frequency with which peripheral neuropathy is the sole presenting feature of Cbl deficiency is a point of controversy. The prevalence and the clinical and electrophysiologic features of Cbl deficiency peripheral neuropathy have not been well characterized. In addition, there is evidence that the commonly used assays of serum Cbl are not adequately sensitive. Testing the serum metabolites methylmalonic acid and homocysteine can increase the identification of Cbl deficient patients. Treatment with parenteral Cbl injections may not produce improvement of neurologic deficits, but might prevent worsening. In some patients with Cbl deficiency, oral Cbl may be an effective therapy.

Homocysteine, cystathionine, methylmalonic acid and B-vitamins in patients with renal disease.

Moderate hyperhomocysteinemia is very frequent in renal patients. Aside from homocysteine (HCY) itself, the metabolites methylmalonic acid (MMA) and cystathionine (CYS) supply further information about disturbances in HCY metabolism. In two groups of renal patients, transplant and hemodialysis patients, we measured HCY, MMA and CYS and evaluated their diagnostic value for impaired HCY metabolism due to vitamin deficiency and renal insufficiency. We investigated serum samples from 63 transplant patients and 38 patients undergoing hemodialysis. HCY, MMA and CYS were assayed by gas chromatography-mass spectrometry, vitamin B6 by HPLC, B12 and folate by chemiluminescence immunoassay. The determination of HCY, MMA, and CYS in renal patients provides specific information about intracellular disturbances of HCY metabolism. The frequency of increased metabolite levels in renal patients was much higher than the frequency of lowered vitamin concentrations in serum. Furthermore, the metabolite levels in transplant patients were only moderately increased, whereas they were strongly increased in patients on hemodialysis (HCY 19.2 vs. 28.8 micromol/l, MMA 292 vs. 1025 nmol/l, CYS 733 vs. 2711 nmol/l). Our findings may support the use of MMA determination in the diagnosis of vitamin B12 deficiency in renal patients. Compared to vitamin B12 deficiency, renal dysfunction itself appears to cause only a modest elevation in serum MMA. Regression analysis revealed that the moderate elevation of HCY and CYS in transplant patients is mainly a consequence of impaired remethylation of HCY to methionine with activated transsulfuration, whereas the mildly elevated MMA level is attributable to renal dysfunction. In patients on hemodialysis, all three metabolites were markedly elevated, indicating a strongly disturbed HCY metabolism. Based on a backward regression, we discovered that the HCY metabolism was strongly disturbed by renal insufficiency and vitamin deficiency. The markedly elevated HCY level was mainly attributable to functional vitamin B12 deficiency indicated by high MMA, and the strong CYS elevation was due to renal dysfunction and inhibition of this pathway by low levels of vitamin B6. In conclusion, besides HCY, the determination of MMA and CYS levels supports an early diagnosis of B-vitamin deficiency in renal patients. MMA is a more sensitive indicator of intracellular vitamin B12 deficiency than vitamin B12 in serum.

Folate Nutrition and Older Adults: Challenges and Opportunities

Folate fortification of bread and grains has been directed to prevent neural tube birth defects. Research has also challenged previous concepts of folate nutritional status and suggested that folate may play a role in reducing the risk of vascular disease. Although folate status of many elderly people is adequate according to traditional, hematologic criteria, some elderly persons have elevated blood concentrations of the metabolite homocysteine, which indicates subclinical deficiency of folate or vitamin B-12. Higher homocysteine concentrations, even within the normal range, are associated with increased risk of vascular disease. Elderly people with better folate and vitamin B-12 status have lower homocysteine concentrations and may have lower risk for vascular disease. Although the new folate fortification rules provide the benefit of increasing folate in the food supply, they could be a risk for the elderly because excess folate intake can mask vitamin B-12 deficiency, thereby delaying diagnosis. Elderly people have a higher prevalence of vitamin B-12 deficiency as a result of absorption problems. Those deficient in vitamin B-12 should be treated to prevent irreversible neurologic damage. Modern approaches to screening the elderly include using higher cutoff points for serum vitamin B-12 and obtaining blood concentrations of the metabolite methylmalonic acid, which is elevated in deficiency of vitamin B-12 but not folate. To examine current folate intake and food sources, food frequency questionnaires were administered to 308 elderly volunteers aged 65 to 94 years. Mean (±standard error) folate intake from food was 299.6±5.8 μg/day. Supplements (median dose=400 μg/day) were consumed by 47% of participants. Only 3.2% of the sample had total folate intake greater than 1,000 μg/day, the recommended upper limit, and these were taking high-dose folate supplements (≥800 μg/day). Breakfast cereals provided 25.6% of folate intake; vegetables, 23.2%; fruit, 20.8%; refined breads/grains, 6.7%; dark bread, 5.0%; legumes/nuts, 5.9%; dairy products, 5.8%; meat/poultry/fish/eggs, 5.1%; other, 1.9%. Mean folate intake would increase 16.5% if enriched bread and grains were fortified. Such fortification could help some persons to lower serum homocysteine concentration and vascular disease risk. Dietitians should be aware of modern protocols for screening the elderly for vitamin B-12 deficiency. J Am Diet Assoc. 1997;97:167–173.

Current concepts in the diagnosis of cobalamin deficiency

Intellectual satisfaction derived from making a correct diagnosis is heightened by the knowledge that treatment, free of side effects, can prevent further progression of disease and may even reverse some or all of the disease manifestations. The paradigm for this situation in neurology has been the disease pernicious anemia (PA), with its associated deficiency of cobalamin (Cbl) leading, if untreated, to progressive spinal cord degeneration, neuropathy, and cerebral complications. There was a time when an astute clinician might have considered that the diagnosis of PA or other causes of Cbl deficiency was relatively simple and treatment straightfor-ward. A patient experiencing neurologic complaints, often affecting sensory and motor function in the lower extremities, would have been found to have macrocytic anemia. To confirm the suspicion, the patient might have had a smooth tongue, prematurely graying hair, lemon-yellow skin, and a family history of anemia requiring monthly ``vitamin shots.'' The diagnosis would have been confirmed by a serum Cbl determination followed by treatment with vitamin cyanocobalamin (vitamin B12; B12). Despite, or perhaps because of, a number of advances in our understanding of Cbl metabolism, we more frequently encounter patients with unusual or atypical clinical and laboratory features who have underlying Cbl deficiency. Subacute combined degeneration of the spinal cord, neuropathy, and other classic manifestations of Cbl deficiency in the nervous system are often easy to recognize, but we now know that there are many atypical presentations. [1-4] Some patients have neurologic syndromes without anemia or macrocytosis, whereas others have a normal serum Cbl level, yet are found to have other biochemical evidence of Cbl deficiency such as raised levels of the metabolites methylmalonic acid and homocysteine. Appropriate investigation is critical, because early treatment affords the possibility of excellent recovery. What are the reasons for this seeming change from …