Hereditary transcobalamin II deficiency: a 22 year follow up

"Progressive myoclonic ataxia and developmental/epileptic encephalopathy associated with a novel homozygous mutation in TCN2 gene"

BACKGROUND

Transcobalamin II (TCN2) defect is a rare metabolic disorder associated with a range of neurological manifestations, including mild developmental delay, severe intellectual disability, ataxia, and, in some cases, seizures. Cobalamin, an essential nutrient, plays a crucial role in central nervous system myelination.

CLINICAL PRESENTATION

We present a family with an index patient who exhibited progressive neurodevelopmental regression starting at 9 months of age, accompanied by myoclonic seizures, ataxia, and tremor. No significant hematological abnormalities were observed. Exome sequencing analysis identified a novel homozygous mutation, c.3G>A - P(Met1I), affecting the acceptor site of intron 4 of the TCN2 gene (chromosome 22: 31003321, NM_000355.4), leading to likely pathogenic variant potentially affecting translation. Following treatment with hydroxocobalamin, the patient demonstrated partial clinical improvement. He has a sibling with overt hematological abnormalities and subtle neurological abnormalities who is homozygous to the same mutation. Both parents are heterozygous for the same mutation.

CONCLUSIONS

In infants presenting with unexplained non-specific neurological symptoms, irrespective of classical signs of vitamin B12 deficiency, evaluation for TCN2 defect should be considered. Early diagnosis and appropriate management can lead to favorable outcomes.

High doses of oral folate and sublingual vitamin B12 in dialysis patients with hyperhomocysteinemia

INTRODUCTION

Folic acid and vitamin B12, alone or in combination have been used to reduce homocysteine (Hcy) levels in dialysis patients.

OBJECTIVES

We aimed to assess the efficacy of high doses of oral folate and vitamin B12 in reducing plasma Hcy levels after a 12-week treatment.

PATIENTS AND METHODS

Thirty-two dialysis patients aged 10-324 months screened for hyperhomocysteinuria. Then cases with hyperhomocysteinemia received oral folate 10 mg/day with sublingual methylcobalamin 1 mg/day for 12 weeks. In pre- and post-intervention phases plasma Hcy concentration, serum folate, and vitamin B12 levels were measured. Changes in plasma Hcy, serum folate, and vitamin B12 concentrations were analyzed by paired t tests, and P values < 0.05 were considered significant.

RESULTS

Eighteen (56.2%) patients had hyperhomocysteinuria. Vitamin B12 and folate levels were normal or high in all cases. Two patients were lost due to transplant or irregular drugs consumption. Plasma Hcy levels were reduced in all, and reached normal values in 50%. A statistically significant differences between first Hcy levels with levels after intervention was found (95% CI, 5.1-8.9, P = 0.0001).

CONCLUSION

Oral folate 10 mg/day in combination with sublingual vitamin B12, 1 mg/day can be considered as a favorable treatment for hyperhomocysteinemia in dialysis patients.

Update on transcobalamin deficiency: clinical presentation, treatment and outcome

Transcobalamin (TC) transports cobalamin from blood into cells. TC deficiency is a rare autosomal recessive disorder usually presenting in early infancy with failure to thrive, weakness, diarrhoea, pallor, anemia, and pancytopenia or agammaglobulinemia. It can sometimes resemble neonatal leukemia or severe combined immunodeficiency disease. Diagnosis of TC deficiency is suspected based on megaloblastic anemia, elevation of total plasma homocysteine, and blood or urine methylmalonic acid. It is confirmed by studying the synthesis of TC in cultured fibroblasts, or by molecular analysis of the TCN2 gene. TC deficiency is treatable with supplemental cobalamin, but the optimal type, route and frequency of cobalamin administration and long term patient outcomes are unknown. Here we present a series of 30 patients with TC deficiency, including an update on multiple previously published patients, in order to evaluate the different treatment strategies and provide information about long term outcome. Based on the data presented, current practice appears to favour treatment of individuals with TC deficiency by intramuscular injections of hydroxy- or cyanocobalamin. In most cases presented, at least weekly injections (1 mg IM) were necessary to ensure optimal treatment. Most centres adjusted the treatment regimen based on monitoring CBC, total plasma homocysteine, plasma and urine methylmalonic acid, as well as, clinical status. Finally, continuing IM treatment into adulthood appears to be beneficial.

Homocysteine and stroke prevention: have the trials settled the issue?

Recent publicity surrounding disappointing results of clinical trials of homocysteine lowering has led to the claim that 'homocysteine is dead'. However, there is strong evidence that elevated plasma total homocysteine is an important independent risk factor, and the highly plausible biological rationale is the following: total homocysteine increases coagulation, impairs endothelial function, increases oxidative stress and low density lipoprotein oxidation, and treatment with vitamins reverses these effects and halts progression of carotid plaque. Some studies have shown clinical benefit of vitamin therapy in coronary angioplasty and peripheral vascular disease. It has recently become apparent that vitamin B12 absorption is impaired in the elderly, and that metabolic B12 deficiency is much commoner than would be appreciated by statistical definitions of 'normal' serum B12; higher doses of B12 and perhaps other therapies such as betaine and thiols may be needed to achieve adequate reductions of total homocysteine. It remains likely that effective lowering of total homocysteine will reduce stroke and other vascular events.

Oral vitamin B(12) and high-dose folic acid in hemodialysis patients with hyper-homocyst(e)inemia

BACKGROUND

Hyper-homocyst(e)inemia is an independent risk factor for atherosclerotic vascular disease in patients with end-stage renal disease (ESRD), although optimal treatment remains unknown. This randomized, double-blind, placebo-controlled study was designed to measure the effect of high-dose oral vitamin B(12) and folic acid on predialysis total homocyst(e)ine levels in patients with ESRD.

METHODS

We studied 81 hemodialysis patients who had hyper-homocyst(e)inemia (>16 micromol/L) on varied doses of a multivitamin containing 1 mg of folic acid/day. After screening blood work, all patients were switched to daily multivitamin therapy, including 1 mg of folic acid for four weeks. For all patients, vitamin B(12), 1 mg/day, was added for an additional four weeks. Patients were then randomized to receive four weeks of 0, 5, or 20 mg of folic acid in addition to the multivitamin and vitamin B(12) (all given daily).

RESULTS

Screening homocyst(e)ine levels (mean 27.7 micromol/L) decreased by 19.2% after four weeks of treatment with a daily multivitamin containing 1 mg of folic acid (P < 0.001). Homocyst(e)ine levels were reduced further from 22.3 to 18.6 micromol/L (mean reduction 16.7%, 95% CI 11.8 to 21.6%, P < 0.001) after four weeks of therapy with vitamin B(12) (1 mg/day). There was no significant difference in mean reduction of homocyst(e)ine levels after therapy with high-dose folic acid compared with placebo (P = 0.35).

CONCLUSIONS

The optimal oral treatment of hyper-homocyst(e)inemia in hemodialysis patients consists of 1 mg of folic acid and 1 mg of oral vitamin B(12) daily. Whether this treatment will lower the risk of future atherosclerotic vascular events remains to be investigated.

Polyneuropathy due to cobalamin deficiency in the rat

In the present study, we investigated the peripheral nervous system (PNS) (both in terms of its ultrastructure and in terms of its function) of rats made cobalamin (Cbl)-deficient either through total gastrectomy or through prolonged feeding on a Cbl-deficient diet. In both these types of Cbl-deficient neuropathies we found: (a) ultrastructurally, intramyelin and endoneural edema, with no or minimal axonal damage in the PNS, in dorsal root ganglia, and the ventral and dorsal rootlets of the spinal cord; (b) electrophysiologically, a significant reduction in the nerve conduction velocity, consistent with that reported in (a); (c) morphometrically, a significant reduction in the density of myelinated fibers both in the sciatic nerve and in the peroneal nerve. All these pathological changes were reversed by chronic postoperative administration of Cbl into totally gastrectomized (TGX)-rats, hinting at the specificity of the damage itself in relation to the permanent Cbl-deficient status of the TGX-rats. No signs of segmental demyelination or remyelination were found. We also observed a turning of type I fibers into type II fibers in the soleus muscle of all our Cbl-deficient rats, however the Cbl deficiency had been induced. This muscular change was still present in TGX- and Cbl-treated rats, and it cannot be related to a malnutrition status, since it has been observed also in rats fed a Cbl-deficient diet. All these results demonstrate that Cbl deficiency strongly affects rat PNS within different parameters.