3.1 Identification of three novel mutations of SLC26A8 in infertile patients with teratozoospermia
In our study, three individuals (patient A, patient B, and patient C) were consulted for primary infertility, and then carried out semen analysis (Table 1). The sperm count of three individuals was basically normal, but of a high percent of morphological abnormalities in sperm. Then we performed WES on the three patients to evaluate the potential genetic causes for their sterile phenotype. Consequently, three latently detrimental heterozygous mutations of SLC26A8 strikingly attracted our attention (Figure 1). The heterozygous frameshift mutations of c.1570_1571del [p.A524*] detected in patient A and c. 306del [p.G103Afs*9] detected in patient C were absent in the general population databases (Table 1). A heterozygous missense mutation of c.2191G>A [p.V731I] was found in patient B and is estimated extremely low allele frequency in public databases (Table 1). Moreover, the site of this missense variant is 100% conserved across several species (Figure S1a).
According to the report of Dirami T et al. , the heterozygous alterations of SLC26A8 contributed to human asthenozoospermia (Dirami et al., 2013). To confirm the patients’ phenotype in detail, we collected their sperm samples to carry out the exhausting morphologic examination. We observed serious frequencies of pyriform-head sperm in patient A, and round-head anomalies in sperm from patient B as well as coiled-tail sperm from patient C under Papanicolaou staining (Figure 2a) and SEM further confirmed that sperm of the patients possessed aberrant head or irregular flagella (Figure 2b). Furthermore, irregular ultrastructure either on the head or flagella was also observed in the spermatozoa of the three patients by transmission electron microscopy (TEM) (Figure 2c). The nucleus in most sperm of patient A was irregular, and patient B showed the larger sperm head with unconsolidated chromatin (Figure 2c). And disorganization of mitochondria helices was detected in the sperm flagella of patient C (Figure 2c). Together, the three patients carrying the heterozygous SLC26A8 mutations showed typical teratozoospermia.