Abstract

BACKGROUND Cryptozoospermia is defined, according to WHO criteria, as the absence of spermatozoa in fresh semen preparations but the presence of rare spe matozoa after centrifugation. Identifying candidate genes and their clinical phenotypes is essential for understanding its etiology and developing targeted therapies. METHODS Whole-exome sequencing (WES) was performed on 503 oligozoospermic and 516 azoospermic infertile patients to identify candidate variants associated with severe male infertility. Functional studies, including protein expression, subcellular localization, and interaction assays, were conducted in vitro, and assisted reproductive outcomes were analyzed. RESULTS We identified a compound heterozygous CHTF18 variant (NM_022092: c.538G > A [p. Val180Met] and c.1434delG [p. Leu481Serfs*3]) in a cryptozoospermic patient exhibiting a high proportion of aneuploid sperm. The missense variant (c.538G > A) was rare (< 0.001% population frequency) and predicted to disrupt protein function by in silico tools. The frameshift variant (c.1434delG) was predicted to introduce premature truncation and a loss-of-function effect. In vitro studies suggested altered subcellular localization of mutant CHTF18 proteins and possible effects on interactions with known binding partners. Despite severe cryptozoospermia, the patient achieved a successful pregnancy and live birth via intracytoplasmic sperm injection (ICSI). CONCLUSIONS These findings support CHTF18 as a candidate gene associated with cryptozoospermia and suggest that biallelic CHTF18 variants may contribute to spermatogenic failure by altering CHTF18 protein localization and interactions within the CHTF18-RLC complex. Further cases and in vivo validation are required to strengthen this gene-disease association.