Homozygous mutations in <i>SPEF2</i> induce multiple morphological abnormalities of the sperm flagella and male infertility.

Abstract

Male infertility due to multiple morphological abnormalities of the sperm flagella (MMAF) is a genetically heterogeneous disorder. Previous studies revealed several MMAF-associated genes, which account for approximately 60% of human MMAF cases. The pathogenic mechanisms of MMAF remain to be illuminated. We conducted genetic analyses using whole-exome sequencing in 50 Han Chinese probands with MMAF. Two homozygous stop-gain variants (c.910C>T (p.Arg304*) and c.3400delA (p.Ile1134Serfs*13)) of the <i>SPEF2</i> (<i>sperm flagellar 2</i>) gene were identified in two unrelated consanguineous families. Consistently, an Iranian subject from another cohort also carried a homozygous <i>SPEF2</i> stop-gain variant (c.3240delT (p.Phe1080Leufs*2)). All these variants affected the long <i>SPEF2</i> transcripts that are expressed in the testis and encode the IFT20 (intraflagellar transport 20) binding domain, important for sperm tail development. Notably, previous animal studies reported spontaneous mutations of <i>SPEF2</i> causing sperm tail defects in bulls and pigs. Our further functional studies using immunofluorescence assays showed the absence or a remarkably reduced staining of SPEF2 and of the MMAF-associated CFAP69 protein in the spermatozoa from <i>SPEF2</i>-affected subjects. We identified <i>SPEF2</i> as a novel gene for human MMAF across the populations. Functional analyses suggested that the deficiency of SPEF2 in the mutated subjects could alter the localisation of other axonemal proteins.