Taking a frequency of 1 in 20,000-25,000 males, De la Chappelle syndrome (46, XX male) is a rare syndrome which exists in different clinical categories with ambiguous genitalia or partially to fully mature male genitalia, in combination with complete or incomplete masculinization. A case of SRY-negative XX male is reported with complete masculinization but with infertility. The patient was mature enough to have full genitalia with descended but small testes and no signs of undervirilization. There were 14 markers in the quantitative fluorescent polymerase chain reaction (QF-PCR): amelogenin gene, presented on X and Y chromosomes allows for the determination of the Y/X ratio (AMEL marker), TAF9B gene presented on chromosomes X and 3 permits the determination of X/chromosome 3 ratio (TAF9B marker or T3 marker), ten non-polymorphic Y-specific markers (SRY, sY84 and sY86 in AZFa region, sY127 and sY134 in AZFb region, sY254, sY255, sY1191, sY1192 and sY1291 in AZFc region), and co-amplification of DAZ/DAZL and CDY2/CDY1 fragments that permit determination of the DAZ, CDY1 and CDY2 gene copy number. The study resulted that there were only two peaks of markers: AMELX/Y marker produced a peak area ratio of 1:0 and T3 with the ratio of 2:2, indicating the presence of two X chromosomes in this case. The absence of the Y chromosome was confirmed when repeating peripheral blood culture for chromosome: there are 46 chromosomes with XX constitution. The first reported case in Mekong Delta, Vietnam is reported of a SRY-negative 46, XX male with normal male phenotype and infertility.

At present, quantitative fluorescent - polymerase chain reaction (QF-PCR) technology is widely being used in prenatal diagnosis of some common genetic syndromes such as Down syndrome, Patau syndrome and Edwards syndrome. The advantages of this technique are its high accuracy, rapid test results and wide applicability. It has used this technique to detect AZF (Azoospermia factor) micro-deletions by Devyser's kit at Tu Du Hospital, Ho Chi Minh City. The novelty of the study was to create a kit with 14 genetic markers and to develop a QF-PCR protocol to detect some common genetic causes in men seeking medical for their infertility with the sperm concentration of ≤ 5 million/ml. We conducted an evaluation in reliability in order to confirm whether the QF-PCR results from the set-up protocol were accurate and reliable. We developed the research on the application of QF-PCR to test for the DNA samples of patients. They were 10 normal reproductive men, 2 patients with Klinefelter syndrome, 4 patients with AZFc micro-deletions, 1 female with normal reproduction. Cordially, we used a sample of water to control the experiment. The results have shown that the kit with 14 genetic markers and the built-in QF-PCR protocol for detecting some common genetic causes in men seeking medical care for their infertility were accurate 100% compared to multiplex-PCR and peripheral blood lymphocyte cultures. The study results are important for identifying some common genetic causes in men seeking medical care for their infertility and helping doctors build the most inferior treatment regimens for their patients. 

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