Analysis Of TMPRSS6 Polymorphisms In Patients With Iron Deficiency Anemia Partially Responsive To Oral Iron Treatment

Iron Refractory Iron Deficiency Anemia (IRIDA) is an autosomal recessive form of iron deficiency anemia (IDA) caused by mutations in TMPRSS6 gene, and characterized by unresponsiveness to oral iron supplementation and low effectiveness of parenteral iron administration (Finberg 2009). So far 50 cases from 32 families have been reported and 40 mutations have been identified (De Falco 2013). Although mutations are extremely rare, recent insights have revealed that highly frequent polymorphisms of TMPRSS6 gene may influence iron absorption, being associated with increased risk of IDA (An 2012).

Between January 2009 and May 2013, 88 subjects (11 males, 77 females) with mean age 39+/-14 years were referred to the Hereditary Anemia Centre of “Fondazione IRCCS Ca’ Granda, Ospedale Maggiore Policlinico di Milano” for persistent IDA poorly responsive to oral iron. All the patients (pts) were investigated for celiac disease, gastrointestinal bleeding, and HP infection. Hematological parameters, iron status, inflammatory markers, and thyroid function were tested. Sequence variation in TMPRSS6 gene was evaluated by PCR and direct sequencing in genomic DNA isolated from peripheral lymphocytes. Thalassemia trait was suspected and investigated in 27/88 (31%) pts (3 males, 24 females) using HPLC and genetic analysis of globin chains. Fifty healthy donors (15 females, 35 males) with mean age 28±9 yrs were used as control group.

Frequency of SNP-120, SNP-113, P33P, K253E, Y418Y, D521D, Δ_15accc and V739Y results significantly different between pts and controls. Association study revealed that in pts homozygosis for V736A is frequently associated with homozygosis for D521D and Y739Y, while polymorphic alleles F5F, P33P, K253E, S361S, Δ_15accc are linked to V736A trans-allele. Based on the observation that homozygosis for V736A is not present in healthy control, we analyzed the hematological parameters in anemic pts homozygotes, heterozygotes, and wild type for V736A. No significant differences were found (table 1). Considering only the thalassemia pts, the combination of thalassemia trait and V736A is associated with a more severe anemia (Hb 10.3±1.4 g/dL, MCV 62.9±6.7 fL median ferritin 30 ng/mL), requiring blood transfusion in particular circumstances (pregnancy, surgery). Moreover, one new variant (H448R) was identified in a pt with IDA requiring parenteral iron supplementation. Two rare variants, A719T and V795I (estimated frequency 0.000/1 and 0.004/9), were detected respectively in two sisters, causing the IRIDA phenotype only in one, and in two patients, who require parenteral iron therapy.

Several TMPRSS6 polymorphisms are more frequent in anemic pts than in healthy donors, suggesting their role in the refractoriness to oral iron. No significant differences were observed in hematological data related to V736A genotype. This is not surprising because all the pts were previously treated with iron therapy, which contribute to partially reduce the degree of anemia. In this study we found peculiar haplotypes, a new variant (H448R) and two rare variants (A719T and V795I), which may account for impairment in TMPRSS6 activity. Further studies are necessary to clarify the role of TMPRSS6 polymorphysms, which will allow identifying individuals at risk for more severe IDA, particularly in thalassemia pts, driving to correct diagnosis and management of iron supplementation, sparing to the patient inadequate therapeutic choices and diagnostic procedures.

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