Cobalamin E defect, a rare inborn error of vitamin B12 metabolism: value of early diagnosis and treatment

Late-onset refractory hemolytic anemia in siblings treated for methionine synthase reductase deficiency: A rare complication possibly prevented by hydroxocobalamin dose escalation?

Methionine synthase reductase deficiency (cblE) is a rare autosomal recessive inborn error of cobalamin metabolism caused by pathogenic variants in the methionine synthase reductase gene (MTRR). Patients usually exhibit early-onset bone marrow failure with pancytopenia including megaloblastic anemia. The latter can remain isolated or patients may present developmental delay and rarely macular dysfunction. Treatment mostly includes parenteral hydroxocobalamin to maximize the residual enzyme function and betaine to increase methionine concentrations and decrease homocysteine accumulation. We report herein 2 cblE siblings diagnosed in the neonatal period with isolated pancytopenia who, despite treatment, exhibited in adulthood hemolytic anemia (LDH >11 000 U/L, undetectable haptoglobin, elevated unconjugated bilirubin) which could finally be successfully treated by hydroxocobalamin dose escalation. There was no obvious trigger apart from a parvovirus B19 infection in one of the patients. This is the first report of such complications in adulthood. The use of LDH for disease monitoring could possibly be an additional useful biomarker to adjust hydroxocobalamin dosage. Bone marrow infection with parvovirus B19 can complicate this genetic disease with erythroblastopenia even in the absence of an immunocompromised status, as in other congenital hemolytic anemias. The observation of novel hemolytic features in this rare disease should raise awareness about specific complications in remethylation disorders and plea for hydroxocobalamin dose escalation.

Ocular manifestations in patients with inborn errors of intracellular cobalamin metabolism: a systematic review

Inherited disorders of cobalamin (cbl) metabolism (cblA-J) result in accumulation of methylmalonic acid (MMA) and/or homocystinuria (HCU). Clinical presentation includes ophthalmological manifestations related to retina, optic nerve and posterior visual alterations, mainly reported in cblC and sporadically in other cbl inborn errors.We searched MEDLINE EMBASE and Cochrane Library, and analyzed articles reporting ocular manifestations in cbl inborn errors. Out of 166 studies a total of 52 studies reporting 163 cbl and 24 mut cases were included. Ocular manifestations were found in all cbl defects except for cblB and cblD-MMA; cblC was the most frequent disorder affecting 137 (84.0%) patients. The c.271dupA was the most common pathogenic variant, accounting for 70/105 (66.7%) cases. One hundred and thirty-seven out of 154 (88.9%) patients presented with early-onset disease (0-12 months). Nystagmus and strabismus were observed in all groups with the exception of MMA patients while maculopathy and peripheral retinal degeneration were almost exclusively found in MMA-HCU patients. Optic nerve damage ranging from mild temporal disc pallor to complete atrophy was prevalent in MMA-HCU.and MMA groups. Nystagmus was frequent in early-onset patients. Retinal and macular degeneration worsened despite early treatment and stabilized systemic function in these patients. The functional prognosis remains poor with final visual acuity < 20/200 in 55.6% (25/45) of cases. In conclusion, the spectrum of eye disease in Cbl patients depends on metabolic severity and age of onset. The development of visual manifestations over time despite early metabolic treatment point out the need for specific innovative therapies.

Delayed Diagnosis of Cobalamin E Defect in an Adolescent Patient

Cobalamin and its metabolites play a critical role in deoxyribonucleic acid synthesis. Disorders of cobalamin metabolism are rare and related with neurological and hematological problems. We report an adolescent patient with cobalamin E (CblE) defect presenting with megaloblastic anemia, mental retardation, cerebral atrophy, cortical visual impairment, white matter changes on brain magnetic resonance imaging, and hyperhomocysteinemia. Homozygous mutation at the c.245C>T in exon 3 of the MTRR gene was identified, which had been found to be related to CblE defect. He was treated with betaine, folic acid, vitamin B6, riboflavin, hydroxycobalamin (OH-B₁₂), and carnitine. During treatment, homocysteine levels decreased over time.

Alterations in methionine to homocysteine ratio in individuals with first-episode psychosis and those with at-risk mental state

BACKGROUND

Disturbance of the methionine (Met) cycle, which produces Met from homocysteine (Hcy), is suggested to be involved in several diseases, including psychiatric disorders. This study was aimed to investigate both levels of Met and Hcy in serum from individuals with first-episode psychosis (FEP) and individuals with at-risk mental state (ARMS).

METHOD

We measured serum Met and Hcy levels in individuals with FEP (n = 13) and ARMS (n = 30) using HPLC with fluorescence detection and LC-ESI-MS/MS. Met and Hcy levels in healthy controls (n = 41) were also measured. Differences between the 3 groups were analyzed by one-way analysis of variance (ANOVA) with Bonferroni correction.

RESULTS

Serum Met levels were decreased (p = 0.038) and Hcy levels were increased (p = 0.017) in the FEP group. Hcy levels were also significantly increased compared to the ARMS group (p = 0.016), while Met levels were not significantly different between the FEP and ARMS groups. A significant decrease in the Met to Hcy ratio (Met/Hcy) was observed in the FEP group compared to both the control (p = 4.58 × 10^-4) and ARMS (p = 8.07 × 10^-3) groups. Furthermore, Met/Hcy ratio was correlated with Positive and Negative Syndrome Scale, especially positive scores (p = 5.90 × 10^-5).

CONCLUSION

Taken together, these data indicate that a decrease in the serum Met/Hcy ratio may be a risk factor for developing psychosis during the transition from ARMS to FEP, and may prove to be a useful marker of the phase between ARMS and FEP.

Clinical onset and course, response to treatment and outcome in 24 patients with the cblE or cblG remethylation defect complemented by genetic and in vitro enzyme study data

BACKGROUND

The cobalamin E (cblE) (MTRR, methionine synthase reductase) and cobalamin G (cblG) (MTR, methionine synthase) defects are rare inborn errors of cobalamin metabolism leading to impairment of the remethylation of homocysteine to methionine.

METHODS

Information on clinical and laboratory data at initial full assessment and during the course of the disease, treatment, outcome and quality of life was obtained in a survey-based, retrospective study from physicians caring for patients with the CblE or CblG defect. In addition, data on enzyme studies in cultured skin fibroblasts and mutations in the MTRR and MTR gene were analysed.

RESULTS

In 11 cblE and 13 cblG patients, failure to thrive, feeding problems, delayed milestones, muscular hypotonia, cognitive impairment and macrocytic anaemia were the most frequent symptoms. Delay in diagnosis depended on age at first symptom and clinical pattern at presentation and correlated significantly with impaired communication abilities at follow-up. Eighteen/22 patients presented with brain atrophy or white matter disease. Biochemical response to treatment with variable combinations of betaine, cobalamin, folate was significant. The overall course was considered improving (n = 8) or stable (n = 15) in 96% of patients, however the average number of CNS symptoms per patient increased significantly over time and 16 of 23 patients were classified as developmentally delayed or severely handicapped. In vitro enzyme analysis data showed no correlation with outcome. Predominantly private mutations were detected and no genotype- phenotype correlations evident.

CONCLUSIONS

The majority of patients with the cblE and cblG defect show limited clinical response to treatment and have neurocognitive impairment.

Outcomes of four patients with homocysteine remethylation disorders detected by newborn screening

PURPOSE

We evaluated the clinical outcome in homocysteine remethylation disorders following newborn screening (NBS) and initiation of early specific treatment.

METHODS

Five patients with remethylation disorders were included in this study.

RESULTS

Two asymptomatic patients (one with cblG and one with cblE) were identified by NBS using an approach that combines a postanalytical interpretive tool (available on the Region 4 Stork (R4S) collaborative project website, http://www.clir-r4s.org) and a second-tier test for total homocysteine determination. Both the initial screening and the second-tier test are performed on the same blood spot, with no additional patient contact, resulting in no false-positive outcomes. Two additional patients with methylenetetrahydrofolate reductase deficiency were detected by NBS using low methionine as a marker. Although already symptomatic despite the early diagnosis, the latter two patients greatly improved with treatment and their outcomes are compared with that of another patient with methylenetetrahydrofolate reductase deficiency and significant morbidity who was diagnosed clinically at 3 months of age.

CONCLUSION

Early detection by NBS and timely and specific treatment considerably improve at least short-term outcomes of homocysteine remethylation disorders. When a remethylation disorder is suspected, group-specific treatment could be started prior to the completion of in vitro confirmatory testing because all disorders from this group require similar intervention.