HIPK4 is a novel gene associated with teratozoospermia and male infertility

Are pathogenic variants in homeodomain-interacting protein kinase (HIPK4) associated with sperm head abnormalities that cause male infertility?

HIPK4 is a novel candidate gene associated with sperm head defects and human male infertility.

Numerous genes have been described in which pathogenic variants cause male infertility due to multiple morphological abnormalities of the sperm flagella (MMAF), but the genetic basis of sperm head defects is less well understood.

This study included four infertile brothers displaying varying degrees of quantitatively and/or qualitatively impaired spermatogenesis, their parents, and their fertile brother. We also queried the Male Reproductive Genomics (MERGE) cohort comprising exome/genome sequencing data of >3300 men.

We performed exome sequencing in all five brothers and their parents. To characterize sperm phenotypes, we carried out standard semen analysis, immunofluorescence staining, and transmission electron microscopy (TEM). Further, we evaluated the impact of the HIPK4 variant in cell culture experiments using HEK293T cells.

By analysing the exome data, we could not identify a common genetic cause in all four affected brothers. However, one of the affected brothers was compound heterozygous for two loss-of-function variants in DNAH17 (c.1076_1077dup p.(Lys360*) and c.7752+2T>A p.?), associated with markedly reduced sperm motility and MMAF. The variants' pathogenicity was further validated by TEM of flagellar cross sections revealing an outer dynein arm defect and axonemal disruption. In contrast, his three infertile brothers were homozygous for the start-loss variant c.1A>G in HIPK4. This gene is expressed during spermiogenesis and is reportedly involved in sperm head shaping in mice. Heterologous expression of (partial) HIPK4 variant cDNA showed that translation was being initiated at an alternative in-frame start codon located 35 amino acids downstream, resulting in an N-terminally truncated protein p.(Met1_Glu35del). The truncated HIPK4 protein lacks parts of its kinase domain and shows reduced protein stability. Corresponding with published mouse models, all three brothers displayed 100% abnormal sperm head morphology with variable defects. Importantly, one brother affected by HIPK4 variants fathered a child after successful ICSI, demonstrating a successful treatment option for HIPK4-related teratozoospermia. No further men from the MERGE cohort were affected by biallelic HIPK4 variants. Taken together, HIPK4 is an autosomal recessive candidate gene in which pathogenic variants are associated with sperm head defects and male infertility.

The reported variants in DNAH17 and HIPK4 have been published in ClinVar.

Independent replication is required to assess the phenotypic spectrum and the reproductive outcome associated with biallelic HIPK4 variants and to formally establish the gene-disease relationship for male infertility.

This study raises awareness of the significant genetic heterogeneity of male infertility. The described family highlights that distinct genetic causes may underlie a seemingly similar phenotype. Exome sequencing of families is helpful to efficiently disentangle individual causes among affected family members.

N.N., J.R., H.O., S.L., C.F., and F.T. were supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Clinical Research Unit 'Male Germ Cells' (CRU326, project number 329621271). R.T.-W., N.N., J.R., H.O., and F.T. were supported by the Federal Ministry of Research, Technology and Space (BMFTR) as part of the project ReproTrack.MS (grant 01GR2303). S.A.K. was supported by the DFG Clinician Scientist programme CareerS Münster (project number 493624047). A.S.G. was supported by the Medical Faculty Münster via an Innovative Medical Research (IMF) grant (GA-122104).

The authors declare no conflicts of interest.