Association between genotype and clinical phenotype in children with primary hemophagocytic lymphohistiocytosis

Objective: To investigate the association between genotype and clinical phenotype in children with primary hemophagocytic lymphohistiocytosis (HLH). Methods: Clinical data of 38 children with primary HLH at Beijing Children's Hospital from November 2015 to October 2020 were analyzed retrospectively. According to whether destructive mutation site, familial HLH (FHL) or non-familial HLH, degranulation pathway and non-degranulation pathway were detected in them, these patients were divided into different groups. Clinical characteristics, laboratory tests and functional tests were analyzed in different groups. Wilcoxon test or chi-square test were used for comparison between groups. Results: Among 38 cases, there were 23 males and 15 females. The age of onset was 2.5 (0.1-13.7) years. PRF1 (13/38, 34%) and UNC13D (12/38, 32%) gene mutations had the highest detectable rate. Correlation analysis between genotypes and phenotypes suggested that patients in destructive mutation sites group (n=25) had a younger age of onset than that in non-destructive mutation sites group (n=13) (1.0 (0.1-9.0) vs. 4.0 (0.4-13.4) years, Z=-2.711, P=0.005). The incidence of central nervous system involvement and convulsion was higher in patients in familial HLH group (n=26) than that in non-familial HLH group (n=12)(62% (16/26) vs. 2/12, χ²=6.631, P=0.015; 54% (14/26) vs. 2/12, χ²=4.656, P=0.040). The levels of soluble CD25, bilirubin, interferon γ (IFN-γ) and interleukin 10 (IL-10) were higher in degranulation pathway impairment group than that in the non-degranulation pathway impairment group (38 444 (2 393-44 000) vs.15 304 (1 620-36 937) ng/L,Z=2.634,P=0.008; 23.5 (6.3-126.4) vs. 6.0 (3.6-31.0) μmol/L, Z=2.992, P=0.003; 20.7 (0-248.7) vs. 11.9 (2.6-21.0) ng/L, Z=2.156, P=0.031; 20.7 (4.3-2 500.0) vs. 11.8 (4.0-88.0) ng/L, Z=2.210, P=0.027). However, the levels of neutrophils, ferritin and lactate dehydrogenase (LDH) in degranulation pathway impairment group were lower in the non-degranulation pathway impairment group (0.5 (0.1-8.0)×109vs. 1.0 (0.9-2.3)×109/L, Z=-3.197, P=0.001; 1 133 (78-10 452) vs. 3 048 (630-37 900) μg/L, Z=-2.407, P=0.016; 410 (188-1 254) vs. 599 (389-3 147) U/L, Z=-2.489, P=0.013). Conclusions: PRF1 and UNC13D gene mutations are most common in primary HLH. Patients with destructive gene mutations have a younger age of onset. Patients with familial HLH are more likely to have central nervous system involvement and convulsions. The levels of sCD25, bilirubin, IFN-γ and IL-10 are higher in the degranulation pathway patients.