A truncating mutation in EPOR leads to hypo-responsiveness to erythropoietin with normal haemoglobin

Abstract

The cytokine erythropoietin (EPO), signalling through the EPO receptor (EPO-R), is essential for the formation of red blood cells. We performed a genome-wide association study (GWAS) testing 32.5 million sequence variants for association with serum EPO levels in a set of 4187 individuals. We detect an association between a rare and well imputed stop-gained variant rs370865377[A] (p.Gln82Ter) in EPOR, carried by 1 in 550 Icelanders, and increased serum EPO levels (MAF = 0.09%, Effect = 1.47 SD, P = 3.3 × 10^-7). We validated these findings by measuring serum EPO levels in 34 additional pairs of carriers and matched controls and found carriers to have 3.23-fold higher EPO levels than controls (P = 1.7 × 10^-6; P _combined = 1.6 × 10^-11). In contrast to previously reported EPOR mutations, p.Gln82Ter does not associate with haemoglobin levels (Effect = -0.045 SD, P = 0.32, N = 273,160), probably due to a compensatory EPO upregulation in response to EPO-R hypo-responsiveness.

Fig. 1

Flowchart depicting the study design. rs370865377[A] (p.Gln82Ter) is the top marker based on corrected P value (P_Corrected = 0.064). Its significance was P = 3.3 × 10⁻⁷ in the GWAS discovery phase. In the replication phase P = 1.7 × 10⁻⁶ and the combined P = 1.6 × 10⁻¹¹. WGS whole-genome sequenced

Fig. 2

Associations of sequence variants with serum EPO levels at the EPOR locus. The mutation p.Gln82Ter in EPOR is labelled as a purple diamond, other variants are coloured according to correlation (r²) with that marker (legend at top-left). –log₁₀P values are shown along the left y-axis and correspond to the variants depicted in the plot. The right y-axis shows calculated recombination rates at the chromosomal location, plotted as a solid blue line. No other correlated sequence variants had a more significant corrected P value than p.Gln82Ter based on variant annotation; none of the highly correlated variants were coding

Fig. 3

Serum EPO concentration of 34 carriers of rs370865377[A] and 34 non-carriers matched by sex, sample collection date, and age at sampling date. Measurements were performed by ELISA. The bottom and top of each box represent the first and third quartiles, the line inside the box is the median and whiskers represent the ±1.5 times the interquartile range. EPO serum levels are plotted on the log-scaled y-axis. The median value of serum EPO concentration of carriers was 3.23-fold higher (median = 22.1 IU L⁻¹; Q1 = 14.1; Q3 = 30.0) than that of non-carriers (median = 6.8 IU L⁻¹; Q1 = 5.4; Q3 = 9.0) (P = 1.7 × 10⁻⁶)

Fig. 4

Schematic diagram of the EPO-R protein product (NP_000112.1) depicting relative location of the N-terminal p.Gln82Ter and reported C-terminal truncating mutations. Y454 and Y456 show strongest affinity to negative regulatory agents and are lost in the reported C-terminal truncating mutations^{, , –, ,} . Functional regions are represented with colours