[Familial fragile X syndrome: A pedigree analysis].

OBJECTIVE

To investigate the clinical (including reproductive) manifestations and genetic characteristics of familial fragile X syndrome (FXS).

METHODS

We collected the clinical data about a case of familial FXS by inquiry, testicular ultrasonography, semen analysis, determination of sex hormone levels, and examinations of the peripheral blood karyotype and Y chromosome microdeletions. Using Southern blot hybridization, we measured the size of the CGG triple repeat sequence of the fragile X mental retardation-1 (FMR1) gene and determined its mutation type of the pedigree members with a genetic map of the FXS pedigree.

RESULTS

Among the 34 members of 4 generations in the pedigree, 3 males and 1 female (11.76%) carried full mutation and 9 females (26.47%) premutation of the FMR1 gene. Two of the males with full FMR1 mutation, including the proband showed a larger testis volume (>30 ml) and a higher sperm concentration (>250 ×10⁶/ml), with a mean sperm motility of 50.5%, a mean morphologically normal sperm rate of 17.5%, an average sperm nuclear DNA fragmentation index (DFI) of 18.5%, a low level of testosterone, normal karyotype in the peripheral blood, and integrity of the azoospermia factor (AZF) region in the Y chromosome. One of the second-generation females carrying FMR1 premutation was diagnosed with premature ovarian failure and another 3 with uterine myoma.

CONCLUSIONS

Some of the FXS males in the pedigree may present macroorchidism and polyzoospermia but with normal semen parameters. In the intergenerational transmission, premutation might extend to full mutation, with even higher risks of transmission and extension of mutation in males, especially in those with >80 CGG triple repeat sequences. Therefore, it is recommended that the couples wishing for childbearing receive genetic testing, clinical guidance, and genetic counseling before pregnancy and, if necessary, prenatal diagnosis and preimplantation genetic diagnosis.