Loss-of-function mutations in SPEF2 cause multiple morphological abnormalities of the sperm flagella (MMAF)

Area of Science:

• Human Genetics
• Reproductive Biology
• Spermatozoa Morphology

Background:

• Multiple Morphological Abnormalities of the Sperm Flagella (MMAF) is a severe form of teratozoospermia leading to male infertility.
• Patients with MMAF exhibit spermatozoa with flagellar defects, including absent, short, coiled, bent, or irregular flagella.
• While mutations in several genes explain 30-50% of MMAF cases, further genetic causes require investigation.

Purpose of the Study:

• To identify novel genetic causes of the human MMAF phenotype.
• To investigate the role of the SPEF2 gene in human male infertility associated with MMAF.

Main Methods:

• Whole exome sequencing was performed on 42 patients with severe infertility and MMAF phenotype.
• Identified mutations in the SPEF2 gene were analyzed for their potential pathogenicity.
• Transmission electron microscopy (TEM), Western blot (WB), and immunofluorescence (IF) were used to assess sperm structure and protein levels.

Main Results:

• Four rare and potentially deleterious mutations (c.12delC, c.1745-2A > G, c.4102 G > T, c.4323dupA) in the SPEF2 gene were identified in two patients.
• TEM revealed disrupted axonemal structure and mitochondrial sheath defects in spermatozoa from affected patients.
• WB and IF analyses showed significantly decreased SPEF2 protein levels in patient spermatozoa.

Conclusions:

• Loss-of-function mutations in the SPEF2 gene are a cause of the MMAF phenotype in humans.
• SPEF2 plays a critical role in maintaining normal sperm tail structure and function.
• This finding expands the genetic basis of male infertility and teratozoospermia.