Genetic Bases of VitaminB12 Deficiency: Impact of MTHFR, TCN-II and

GIF Polymorphisms on Vitamin B12 Level

MAZHAR SALIM AL ZOUBI

The Deanship of Scientific Research and Graduate Studies at Yarmouk University, Irbid, JORDAN

Abstract— Vitamin B12 deficiency is associated with serious health problems such as neurological disorders. In Jordan, few studies have

evaluated the level of vitamin B21 in the Jordanian population with different prevalence. Genetic predisposition, lifestyle, environment,

socioeconomic status, and geographic have been linked to vitamin B12 deficiency. Polymorphisms in the GIF, MTHFR, and Transcobalamins,

have been proposed to be associated with the level of vitamin B12. The aim of the current study was to evaluate the impact of certain

polymorphisms in MTHFR, TCN-II and GIF genes on the level of vitamin B12 in the Jordanian population. Polymorphic sites of the MTHFR

(c.677 C>T, rs1801133 and c.1286A>C, rs1801131), TCN2-776C>G (Arg259Pro) (rs1801198) and GIF-68 A>G (Q5R) genes were analyzed

by RFLP and DNA sequencing in a group of vitamin B12 deficient individuals (n = 100). The control group included 100 matching

individuals with a normal level of vitamin B12 (>200 ng/mL). Our results showed a significant association between the homologous variant of

the TCN2 gene (G776G) and MTHFR c.677C>T genes and vitamin B12 deficiency. On the other hand, The MTHFR c.1286A>C variant and

GIF variants did not show significant association with vitamin B12 deficiency. This study expounds the association of TCN2 and MTHFR

polymorphisms with cobalamin levels in a Jordanian population and highlights the necessity of further studies to elucidate the molecular basis

and impact of TCN2, GIF, and MTHFR gene polymorphisms on vitamin B12 deficiency and associated disorders.

Keywords— MTHFR, TCN-2, GIF, Polymorphisms, Vitamin B12 Deficiency.

Received: March 20, 2021. Accepted: December 6, 2021. Published: January 4, 2022.

1. Introduction

Cobalamin (Vitamin B12) is an essential vitamin for the

synthesis of methionine, DNA, red blood cells and the myelin

of the nerve cells [1-3]. Therefore, it is crucial to be obtained

from the natural sources such as meat, milk, and eggs [4].

Naturally, vitamin B12 deficiency is caused by malnutrition,

malabsorption or genetic predisposition and it takes up to 5

years to develop [5-7]. Vitamin B12 deficiency can lead to

serious pathology including megaloblastic anemia and certain

neurological disorders [8-12]. In Jordan, vitamin B12

deficiency is a serious health concern. However, few studies

have evaluated the level of vitamin B12 in the Jordanian

population with different prevalence [13-17].

Many factors have been proposed to be associated with the

deficiency of vitamin B12 including genetic predisposition,

lifestyle, environment, socioeconomic status and geography

[17-19]. For instance, certain polymorphisms in the gastric

intrinsic factor, MTHFR, and Transcobalamins have been

found to be related to the level of vitamin B12 [20-22].

Furthermore, in an interesting Chilean study, Cabrera et al.

reported that the deficiency of vitamin B12 is associated with

the UV light exposure [19].

Geographically, Jordan is a Middle East country, located in

Southwest Asia and northern of Tropic of Cancer. Despite the

small size of Jordan, the geography in Jordan is very diverse

and includes the lowest point on the earth (Dead Sea).

In this study, we aimed to evaluate the prevalence of vitamin

B12 deficiency, and genetic polymorphisms of TCN-2,

MTHFR and GIF genes in Jordanian population in different

geographical locations.

2. Materials and Methods

The study population included 2,880 Jordanian individuals

(890 men and 1990 women) from four governorates covering

three geographical locations in Jordan (Irbid, Karak, Maan,

and Tafilah). Blood samples were collected in EDTA tubes

after signing the informed consent form which was approved

by the research ethics committee at Yarmouk University. 200

samples (100 with vitamin B12 deficiency and 100 as a control

group) were selected for genetic study of the polymorphic

variation in three genes (TCN-2, MTHFR and GIF) including

four SNPs.

Genomic DNA extraction was performed by using

commercially availble kit from Qiagen (QIAamp® DNA

Blood Mini Kit (QIAGEN, Germany) According to the

manufactuer's instructyions. The last wash was removed and

the pellet mixed with 100 uL of TE buffer and stored at – 20°

PCR, RFLP and DNA sequencing were performed as

described before [23, 24].

3. Results

Univariate OR showed an increase in the risk of low vitamin

B12 with increasing age in men and women. Both univariate

OR and age-adjusted OR in men showed a significant decrease

in low vitamin B12 risk in the region of Tafela when compared

to Irbid. The similar significant lower risk was observed in

WSEAS TRANSACTIONS on BIOLOGY and BIOMEDICINE

DOI: 10.37394/23208.2022.19.2

Mazhar Salim Al Zoubi

E-ISSN: 2224-2902

Volume 19, 2022

women from Maan and Tafela. No significant change in risk

was found in women reporting pregnancy or newborns.

Our results showed a significant association between

homologous G776G genotype of the TCN2 gene and the low

level of vitamin B12 (p < 0.05). On the other hand, the

genotype distribution; A68G genotypes of the GIF gene did

not show significant association with the deficiency of vitamin

B12 (p = 0.2)

DNA sequencing analysis for the C677T polymorphisms of the

MTHFR gene showed that the frequency of homozygous CC

genotype is lower in the B12 deficient individualscompared to

the control group. Hence, the C677T genotypes frequencies

distribution revealed a significant difference in individuals

with vitamin B12 compared to controls. B12 deficient

individuals did not show any significant difference in the

genotypes frequencies distribution for the A1298C

polymorphisms in comparison with the control group.

4. Discussion

In the current study, we found a significant difference in B12

level between different geographical groups. The northern

population showed the lowest level of vitamin B 12 and the

highest percentage of deficient individuals in comparison with

the other groups. On the other hand, the southern populations

showed a higher level of vitamin B12 and lowest percentage of

vitamin B 12 deficiency. Our findings are consistent with

previous reports that underscored the health problem of

vitamin B12 deficiency in Jordan [17, 25-27]. The southern

population showed a higher level of vitamin B12 and a lower

percentage of deficiency. Therefore, we are suggesting the role

of other genetic, lifestyle, dietary and environmental factors

that could be associated with vitamin B12 level in Jordan.

Genetically, the results suggest that the homologous G776G

genotype of the TCN2 gene and MTHFR T677T genotype

have significant association with vitamin B12 level in a

Jordanian population. On the other hand, the A68G genotype

of the GIF gene and the 1298A>C polymorphisms of the

MTHFR gene did not show an association with the deficiency

of B12 showed no significant association with B12 deficiency.

Combination of the four geneotypes showed a higher

associoation between the tested polymorphisms and the

presence of vitamin B12 deficiency in the Joprdanian

population. Further studies are required to elucidate the impact

of TCN2, GIF and MTHFR genes polymorphisms on B12

indices and B12 associated disorders.

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Appendex

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DOI: 10.37394/23208.2022.19.2

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