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.