Genes and pathways underpinning Klinefelter syndrome at the single-cell level

Klinefelter syndrome (KS) is the most frequent genetic anomaly in infertile males. Despite this, the molecular mechanisms involved in KS are poorly defined. Based on bulk transcriptome and single-cell RNA sequencing datasets with peripheral blood monocyte (PBMC) sample(s) from healthy and KS men, this study was designed to address critical genes and pathways correlated with the occurrence of KS. Through a comparison between control and KS samples, we obtained 5 hub genes, including two upregulated genes (XG and ITLN1) and three downregulated genes (DEFA4, BPI and MPO). Without exception, these five genes yielded an excellent discriminatory capacity for KS with an area under the receiver-operator-characteristic curve over 0.75. We also assessed between-group differences of immune cell infiltration using ssGSEA. Infiltrated degree of some immune cells such as CD56 bright NK cell was found to be positively associated with the expression of ITLN1 and XG. Through Kyoto Encyclopedia of Genes and Genomes enrichment, we identified PI3K/AKT pathway and neuroactive ligand-receptor interaction as upregulated pathways for KS. Gene set enrichment analysis together with gene set variation analysis confirmed upregulation of G2M checkpoint, mitotic spindle, and heme metabolism for KS. Furthermore, scRNA-seq data analysis was conducted to detect intercellular communication between different immune cell types, and a strong correlation was detected for macrophages, dendritic cells or NK cells with the other cell types. Collectively, we provided hub genes, pathways, immune cell infiltration degree, and cell-cell communication interactions for KS, warranting novel insights into the mechanisms of KS.