IRIDA Phenotype in TMPRSS6 Monoallelic-Affected Patients: Toward a Better Understanding of the Pathophysiology

Genomics of iron refractory iron deficiency anemia phenotype reveals a spectrum of novel pathogenic biallelic and monoallelic TMPRSS6 variants and rare overlapping disorders

The study highlights genomic findings in a series of 13 IRIDA phenotype cases. All had microcytic hypochromic anemia with suboptimal oral iron response to two different oral iron preparations at 4-6 weeks and low-normal ferritin, low transferrin saturation, and inappropriately high hepcidin. Targeted NGS on a 26-gene iron panel revealed pathogenic TMPRSS6 variants in 5/13 (38 %) cases. In addition, 2 (15 %) cases revealed rare SMAD4 and TBXAS1 gene variants that can present with refractory anemia but were consistent with diagnosis of hereditary hemorrhagic telangiectasia and Ghosal hematodiaphyseal dysplasia respectively.

Common Single Nucleotide Polymorphism of TMPRSS6, an Iron Regulation Gene, Associated with Variable Red Blood Cell Indices in Deletional α-Globin Genotypes

Red blood cell (RBC) indices, including mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH), have been widely used for primary screening for thalassaemia (thal) syndromes. Recently, a single nucleotide polymorphism (SNP) rs855791 of TMPRSS6, an iron regulation gene involved in the substitution of a nucleotide between thymine (T) and cytosine (C) in exon 17 resulted in an amino acid change, p.Val736Ala (V736A), has been described to associate with RBC indices. The objective was to study the effects of common SNP V736A on RBC indices in deletional α-thal variations. SNP rs855791 genotypes were identified from 433 Thai volunteers, including 32.6% males and 67.4% females with an average age of 23.0 ± 8.7 years. These populations included individuals (82.4%) who had normal globin genotype (αα/αα, ββ) and α-thal carriers, which were divided into two subgroups, including α⁺-thal (-α/αα) (14.1%) and α^o-thal (--/αα) (3.5%). Among three SNP genotypes, the C allele gradually expressed higher MCV and MCH than those of the T allele in both α⁺- and α^o-thal traits. Importantly, SNP rs855791 of TMPRSS6 responded to α-globin deletions for sustaining RBC sizes and haemoglobinisation in α-thal carriers.