Long term biweekly 1 mg oral vitamin B12 ensures normal hematological parameters, but does not correct all other markers of vitamin B12 deficiency. A study in patients with inherited vitamin B12 deficiency

Parenteral vitamin B₁₂ is considered the treatment of choice for vitamin B₁₂ deficiency, but also treatment with 1–2 mg daily oral vitamin B₁₂ is recommended.1,2 Recently, alternative regimes have been proposed, such as an oral dose of 1 mg vitamin B₁₂ daily for ten days, weekly for four weeks, and monthly or biweekly for life.3,4 One short-term study assessed this regime employing hematologic markers and total plasma cobalamins.4 It is unclear to what extent the patients included had a total or only a partial lack of active absorption of vitamin B₁₂.

In the present study, we examined the long-term efficacy of biweekly oral treatment with 1 mg vitamin B₁₂ by studying hematologic parameters, cobalamins, methylmalonic acid (MMA), total homocysteine (tHcy), and cobalamin saturated transcobalamin (holo-TC) in patients with congenital vitamin B₁₂ deficiency treated for at least five years, patients not following this treatment for at least one year, their biological parents, and healthy controls.

Patients (n=16) were unable to actively absorb vitamin B₁₂ because of defects in the cubilin or amnionless receptors (n=12) or inherited lack of intrinsic factor (IF) (n=4). Genotyping was available for 11 patients.5–7 Lack of vitamin B₁₂ absorption was recently confirmed in all 16 patients.7 After the initial diagnosis, all 16 patients except 2 (patients # 4,16) received 100 μg vitramin B₁₂ intramuscularly daily during the first week, every other day during the second week, twice a week until the hemoglobin had normalized, and every month thereafter. This treatment regime was changed to biweekly 1 mg oral treatment in 1996. Patients #4,16, diagnosed in 1997, received only oral treatment as indicated above after a loading dose of 1 mg oral vitamin B₁₂ daily for ten days and 0.5 mg oral vitamin B₁₂ daily for an additional ten days.3 Cobalamin (cyanocobalamin) (1 mg ampoule, Deva) was mixed with water or fruit juice and was self-administered orally. Blood sampling was performed two weeks after the last oral intake of vitamin B₁₂ in 2003. Four of the patients (#3, 4, 11, 17) initially followed the biweekly oral treatment as described above but did not receive any treatment with vitamin B₁₂ for at least one year prior to the study. We included parents of the patients who were all expected to be heterozygous for the inherited vitamin B₁₂ deficiency (n=19), and healthy controls (n=44) with no clinical evidence for vitamin B12 deficiency. Inclusion criteria were no known disorders related to vitamin B₁₂ deficiency, no chronic systemic disease and no medical treatment, including vitamin tablets, within the previous week.

Table 1A.Data on patients with congenital vitamin B₁₂ deficiency treated or not with oral vitamin B₁₂, their parents and healthy individuals (controls). Median and range is indicated, Table 1A.

Table 1B.Data for each of the included patients.

Figure 1.Biochemical indices in patients with congenital vitamin B₁₂ deficiency and in control groups. The median values for hematologic and vitamin B₁₂ indices are presented in 1) patients with congenital vitamin B₁₂ deficiency not treated biweekly with 1 mg oral vitamin B₁₂ for at least one year (n=4, Pt. −B12), 2) such patients treated biweekly with 1 mg oral vitamin B12 for at least five years (n=12, Pt. + B₁₂), 3) the obligate heterozygous biological parents (n=19), and 4) healthy controls (n=44). The dotted vertical lines represent upper or lower values of the reference interval calculated from values obtained for the control group. MCV; middle cell volume, MMA: methylmalonic acid, tHcy: total homocysteine, Holo-TC: cobalamin saturated transcobalamin.

Laboratory data and other information on all patients and controls are indicated in Tables 1A and 1B. The Research Ethics Committee of Hacettepe University Hospital approved the study protocol.

Cobalamins was measured on the Advia Centaur Analyzer (CV<10%). Serum holo-TC was measured by an in-house ELISA (CV<10%).8 MMA and tHcy were determined by gas chromatography–mass spectrometry after derivatization with methylchloroformate9 (CV < 4%). Hematologic parameters were measured using a Beckman Coulter.

All patients with congenital vitamin B₁₂ malabsorption showed an increase in hemoglobin and most of them showed a decrease in MCV between the time of diagnosis and the time of the current study (Table 1B). At the time of the study there was no difference in hematologic parameters (Table 1A) between patients with congenital vitamin B₁₂ malabsorption and the control groups. The four untreated patients had low serum cobalamins, and holo-TC concentrations, elevated tHcy and MMA (p<0.001) as compared to values obtained for the controls, but, unexpectedly, normal hematologic parameters (Table 1A, Figure 1).

For the 12 treated patients, no markers except for holo-TC (p<0.001) showed a significant difference to those of the control subjects and their biological parents (Table 1A). However, values not within normal range as calculated from controls was observed for some of the 12 treated patients; MMA>0.51 μmol/L (n=4), tHcy>22 μmol/L (n=1), cobalamin <126 pmol/L (n=2) and holo-TC<21 pmol/L (n=8).

The main findings of the present study on patients with congenital vitamin B₁₂ deficiency are that biweekly oral treatment with 1 mg vitamin B₁₂ ensures normal hematologic parameters, but does not correct all other markers of vitamin B₁₂ deficiency. Thus, vitamin B₁₂ deficiency may exist in this population without hematologic signs, as previously demonstrated in other populations.10

Studies by Gangorase et al.11 and subsequently by Altay and Cetin3 showed that anemia due to inherited vitamin B12 deficiency could be corrected by oral vitamin B₁₂. In the latter study, biweekly 1 mg oral vitamin B₁₂ treatment after a loading dose was sufficient for maintenance of normal hematologic parameters and cobalamin levels during a follow-up period of 12 months. Our study challenges the conclusion that biweekly 1 mg vitamin B₁₂ treatment is sufficient and questions hematologic parameters and plasma cobalamins as measures of inadequate vitamin B₁₂ status.

Elevated plasma concentrations of MMA and tHcy can be used as biochemical markers to aid in the diagnosis of vitamin B₁₂ deficiency and to monitor the response to cobalamin supplementation. In our study, more than 75% of the patients with congenital vitamin B₁₂ deficiency treated biweekly with 1 mg oral vitamin B₁₂ for more than five years had normal levels of MMA and tHcy, but only 33% had a normal holo-TC. This observation agrees with the view that holo-TC is an early marker of a suboptimal vitamin B12 homeostasis.12

In conclusion, biweekly treatment with 1 mg vitamin B₁₂ seems to normalize indices of vitamin B₁₂ status in some, but not all of the patients with congenital vitamin B₁₂ deficiency. We, therefore, believe that a more frequent intake of oral vitamin B₁₂ is required, but we question whether a daily dose of 1–2 mg vitamin B₁₂ is needed.

Acknowledgments

we warmly acknowledge the excellent technical assistance of Anna-Lisa Christensen and Jette Fisker Pedersen.

Footnotes

• Funding: this work was supported in part by a European Union demonstration project on the diagnostic utility of holo-TC (QLK3-CT-2002-01775).