Here, the data from our human sperm bank showed that, other than three-generation family history analysis, specific gene testing and whole exome sequencing can be used for the genetic testing of sperm donors.
In China, sperm donor eligibility at sperm banks is determined in part by infectious disease screening and family history risk assessment. Routine testing for genetic disease is becoming increasingly important as part of the donor selection process due to the rising number and expanding availability of genetic tests. Meanwhile, recipients’ demands for sperm donor genetic testing are also increasing, which has influenced donor screening and selection at human sperm banks. Unlike sperm banks in the United States, reasons for presenting for the use of sperm donor in China can only be that current partner has fertility issues. Therefore, lots of recipients who do not unacceptable sperm donors may also have genetic diseases. However, the sperm donor screening guidelines do not describe how genetic tests published by the Chinese Ministry of Health in 2003 , which are currently in effect , should be performed.
That at the base of criteria for sperm donor screening in China, sperm donors whose semen parameters up to standard would undergo further physical and laboratory examinations, including three-generation family history analysis, karyotype analysis and so on. In addition, our sperm bank has increased the screening of thalassemia and G6PD for qualified sperm donors. Thalassemia is considered one of the most common genetic disorders resulting from globin chain synthesis impairment because of the mutation or deletion of globin gene, such as α- and β-thalassemia, with a high frequency in Southeast Asia . In recent years, large-scale surveys for thalassemia have been conducted in different parts of China, and its prevalence remains high[12, 13]. A prevalence map based on a geographic information system (GIS) showed that the geographic distribution of thalassemia was highest in the south of China, including Guangdong, Guangxi, Guizhou, Yunnan and so on, and decreased from south to north . In the present study, we used blood routine testing to screening of thalassemia related gene carriers in qualified sperm donors, if blood routine results showed a decrease in mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), accompanied by an increase in red cell count (RBC), we would think that the sperm donors were suspected thalassemia related gene carriers, whom would be eliminated. Because of less globin production, the thalassemia RBC showed microcytic and hypochromic, MCV, MCH and RBC were valuable indicators for screening thalassemia related gene carriers [15–17]. However, MCV, MCH and RBC cannot discriminate between α- and β-thalassemia, and cannot discover heterozygous thalassemia related gene carriers. Even so, 2.4% of sperm donors (80/3231) were suspected thalassemia related gene carriers, which was significantly lower than another study in Hunan province that analyzed by using Next-Generation Sequencing. G6PD deficiency is one of the most common X-linked enzymopathies caused by G6PD gene variants, and G6PD deficiency is a common genetic disease in China. The incidence of G6PD deficiency in China is also characterized by a high to low gradient distribution from the south to north regions . In the present study, we used RDT to diagnosis G6PD deficiency in qualified sperm donors, which can accurately identify hemizygous males and homozygous females. The data showed that 1.4% of sperm donors (56/3231) were G6PD deficiency whom would be eliminated. The overall prevalence of G6PD deficiency in China was 2.10% at the national level, and in Hunan province was 1.13% , which was similar to our results. Therefore, through the interpretation of blood routine and RDT results of sperm donors, it can make a preliminary screening of thalassemia and G6PD deficiency, and improve the laboratory examination of sperm donor genetic testing.
As early as 2010, all sperm banks in the United States have conducted some degree of genetic testing on their sperm donor applicants as part of the screening process. Furthermore, cystic fibrosis (CF) carrier screening, hemoglobin evaluation, and chromosome analysis are performed routinely for the majority of donor applicants . CF is one of the most common severe AR diseases in the white population, with an approximate incidence of 1 in 2500 live births . However, it is least common in Africans and Asians . Therefore, CF carrier screening is not available at human sperm banks in China. Our data show that sperm donor carrier screening for the thalassemia-related genes was the most requested by recipients. Meanwhile, recipient requests for sperm donor carrier screening for G6PD genes were only second to that for thalassemia. 1.9% of 154 donors (3/154) as carrier variants in α-Like or β-Like globin genes, although thalassemia and G6PD deficiency have been preliminary screened. This also shows while MCV, MCH and RBC were valuable indicators for screening thalassemia related gene carriers, genetic testing is the gold standard for diagnosing thalassemia related gene carriers. The incidence of genetic disease varies in different regions in China. Hence, genetic testing of sperm donors should be performed with targeted genetic disease-related genes of the different regions. In particular, donors of semen for external use in the Guangxi and Guangdong provinces in south China, which have a high incidence of thalassemia and G6PD deficiency, should be tested for the α-like, β-like globin genes and G6PD gene.
In the present study, carrier genetic testing was performed using NGS, which was first used in infertile couples wishing to conceive through ART in 2015. In the clinical dataset, 2161 samples (84%) tested positive, with an average carrier burden of 2.3 variants per sample. Five percent of the couples wishing to conceive through ART were carriers for the same mutation; genetic screening prevented the birth of 1.25% of genetically affected babies born after ART . Carrier genetic testing can be applied to couples wishing to conceive through ART, as well as ART with sperm or oocyte donors, to avoid serious monogenic genetic diseases . Comparison with the Exome Aggregation Consortium (ExAC) East Asian and European populations showed that the carrier frequency of disease-related genes identified at the Translational Medicine Center of the Children’s Hospital of Fudan University is much more similar to that of the East Asian population than the European population. The difference in carrier frequency among populations should not be ignored and makes it necessary to establish a Chinese-specific panel for genetic testing . In the present study, we performed whole exome sequencing carrier screening, which included more than 5000 genes associated with more than 7000 disorders in OMIM. We tested 43 sperm donors, with an average carrier pathogenic/likely pathogenic variant of 2.58 per sample. Forty-five cycles of preassigned donor–recipient matches were identified, 25 clinical pregnancies were achieved, and 18 offspring was delivered. Although the data are based on a limited number of participants, the results provide the carrier frequencies for many recessive disorders. Here, we found that, for many of the studied genes, the carrier frequencies for some of the most common recessive disorders, such as GJB2-related DFNB1 nonsyndromic hearing loss and deafness, citrullinemia argininosuccinate synthase deficiency, late-onset Alzheimer disease, and AR mental retardation, are higher than that previously reported [26–29]. This is not unexpected, as previous studies on carrier frequencies were based on known mutations, whereas here we explored the entire coding region of most genes. In addition, eight of 43 donors (18.6%) were carriers of pathogenic or likely pathogenic variants in GJB2; the frequency therefore was approximately 1 in 5. Meanwhile, in special gene testing, three of 17 donors (17.6%) also as carrier variants in GJB2. However, as different GJB2 pathogenic variants are associated with various phenotypes of hearing loss. For instance, both c.109G > A homozygotes and compound heterozygous c.109G > A variants of GJB-2 indicate a significantly higher risk of developing hearing loss. Conversely, heterozygous c.109G > A variants alone do not increase the risk of hearing loss . In the present study, five of 8 variants were heterozygous c.109G > A variants, that do not increase the risk of hearing loss. Although the carrier frequencies of GJB2 should not be over-interpreted, the frequency of GJB2 variants should be a concern in sperm donors in China.
Whole exome sequencing and specific gene carrier screening are powerful tools, especially for certain high-risk ethnic populations. However, there is considerable debate within the sperm banking community as to which tests should be included in the donor application process, in part because genetic testing is expensive and adds considerably to the cost of qualifying as a sperm donor. Nonetheless, there is no guideline in China on the proper use of sperm samples after genetic testing, which also limits the application of genetic screening in sperm banks in China. However, many inherited risks cannot be detected before donor qualification even when a thorough genetic family history evaluation has been performed. Hence, genetic testing for sperm donors can improve the quality of donor screening effectively and reduce the genetic risks for the offspring. Meanwhile, genetic testing was required not only for sperm donors but also for recipients, aid a successful and healthy pregnancy. In additions, it is important that human sperm banks engage the services of genetics professionals so that their clients have access to counseling about their family’s medical histories and the value and limitations of genetic testing and its role in reducing the risk of birth defects in future offspring.
Our study has some limitations: we did not perform genetic testing of the donors’ offspring, as congenital abnormalities were not reported therein. Furthermore, our study is not based on the all general population wishing to conceive, as the study group consisted of sperm donors who were young men. Although 321 qualified sperm donors underwent genetic testing, a larger cohort would provide more information. More studies of this type are needed.
This is the first study to investigate genetic testing of donor specimens from a sperm bank in China. Our results are significant for sperm donors, recipients, and future offspring. The data clearly illustrate that the significant risks presented by donors include inherited susceptibility for AR and undiagnosed AD disorders, and suggest that used blood routine and RDT can make a preliminary screening of sperm donors, and special gene testing be performed for sperm donors according to the regional incidence of specific genetic diseases. Meanwhile, whole exome sequencing can be used as a supplementary application in sperm donor genetic testing, and aid a successful and healthy pregnancy. However, industry guidelines must be modified to incorporate its use.