Nucleoside diphosphate-linked moiety X-type motif 15 R139C genotypes impact 6-thioguanine nucleotide cut-off levels to predict thiopurine-induced leukopenia in Crohn’s disease patients

Table 1 Characteristics of the 411 Crohn’s disease patients included in this study

Characteristic	All patients	With leukopenia	Without leukopenia	P value
No. of subjects (%)	411	72 (17.5)	339 (82.5)	-
Gender
Male, n (%)	305 (74.0)	52 (17.0)	253 (83.0)	0.180
Female, n (%)	106 (26.0)	20 (18.9)	86 (81.1)
NUDT15 R139C
CC, n (%)	342 (80.4)	35 (10.2)	307 (89.8)	2.40 × 10-15
CT, n (%)	65 (17.9)	33 (50.2)	32 (49.8)
TT, n (%)	4 (1.7)	4 (100)	0
TPMT*3C				0.26
AA, n (%)	398 (96.8)	68 (17.1)	330 (82.9)
AG, n (%)	13 (3.2)	4 (30.8)	9 (69.2)
Age in years, median (range)	28 (12-70)	26(12-70)	27(12-60)	0.734
Medication
Azathiopurine	337 (82.0)	57 (17.3)	273 (82.7)	0.113
Mercaptopurine	74 (18.0)	14 (18.9)	60 (81.1)
Thiopurines dose, mg/kg per day, median (range)	1.7 (0.2-3.1)	1.5 (0.5-2.6)	1.7 (0.2-3.1)	0.030
CD
Ileal L1	34	6	28	0.495
Colorectal L2	21	6	15
Ileocolonic L3	292	48	244
Upper gastrointestinal L4	61	12	49
Co-medication	211	45	166	0.74
Corticosteroids	79	15	64
Thalidomide	51	13	38
Anti-TNF agent	64	13	51
5-ASA	4	0	4
Allopurinol	13	4	9

Patients carrying the nucleoside diphosphate-linked moiety X-type motif 155 R135C CT and TT genotypes were more likely to develop thiopurine-induced leukopenia (^bP < 0.01). NUDT15: Nucleoside diphosphate-linked moiety X-type motif 15; CD: Crohn’s disease.

Table 2 Relationship between concentrations of 6-thioguanine nucleotide and thiopurine-induced leukopenia in different nucleoside diphosphate-linked moiety X-type motif 15 R139C genotype groups among 411 patients according to receiver operating characteristic curves

NUDT15 genotype (No. of patients)	6TGNs (pmol/8 × 108 RBC)	P value	AUC	95%CI	Sensitivity (%)	Specificity (%)
CT + CC	≥ 474.7	0.071	0.57	(0.49-0.65)	34.7	82.6
CC (342)	< 474.7	9.4 × 10-5		(0.61-0.79)	60.0	73.3
	≥ 411.5		0.70
	< 411.5
CT (65)	≥ 319.2	0.039	0.65	(0.51-0.79)	42.4	96.9
	< 319.2

In subgroups, the area under the curve was increased from 0.57 to 0.65 and 0.70. Moreover, in the CT group, the specificity was as high as 96.9%, with a sensitivity of 42.4%, and in the CC group, the specificity was 73.3%, with a high sensitivity of 60.0%, compared with the values in the total samples. AUC: Area under the curve; NUDT15: Nucleoside diphosphate-linked moiety X-type motif 15; RBC: Red blood cells.

Table 3 Multivariable prediction model for thiouprine-induced leukopenia, including the nucleoside diphosphate-linked moiety X-type motif 1 R139C genotypes and 6-thioguanine nucleotide cut off levels

Category	Leukopenia		% of total	OR (95%CI)	P value
	Yes	No
NUDT15 R139C TT	4	0	4/4 (100%)	↑↑↑	-
NUDT15 R139C CT + 6TGN > 319.2	14	1	14/15 (93.3%)	225.0 (27.6-1836.2)	1.5 × 10-14
NUDT15 R139C CT + 6TGN < 319.2	19	31	19/50 (38.0%)	9.9 (4.5-21.6)	8.1 × 10-11
NUDT15 R139C CC + 6TGN > 411.5	21	82	21/103 (20.4%)	4.1 (2.0-8.5)	4.8 × 10-5
NUDT15 R139C CC + 6TGN < 411.5	14	225	14/239 (5.9%)	Reference	-
Total	72	339	72/411 (17.5%)

Patients carrying the TT allele, irrespective of the concentration of 6-thioguanine nucleotide (6TGN), were at the highest risk, as all of them developed leukopenia in this study. Patients with the CT genotype and a 6TGN concentration above the cut-off value of 319.2 pmol/8 × 10⁸ red blood cells (RBC) were at the second highest risk of developing leukopenia [OR 225.0 (95%CI: 27.6-1836.2)], followed by those carrying the CT genotype with a 6TGN concentration below 319.2 pmol/8 × 10⁸ RBC [OR = 9.9 (95%CI: 4.5-21.6)] and those carrying the CC genotype with a 6TGN concentration above 411.5 pmol/8 × 10⁸ RBC [OR 4.1 (95%CI: 2.0-8.5)]. NUDT15: Nucleoside diphosphate-linked moiety X-type motif 15; 6TGN: 6-thioguanine nucleotide.