Hypogonadotroper Hypogonadismus aufgrund eines IHH oder Kallmann-Syndroms beim Mann

MECHANISMS IN ENDOCRINOLOGY: Aberrations of the X chromosome as cause of male infertility

Male infertility is most commonly caused by spermatogenetic failure, clinically noted as oligo- or a-zoospermia. Today, in approximately 20% of azoospermic patients, a causal genetic defect can be identified. The most frequent genetic causes of azoospermia (or severe oligozoospermia) are Klinefelter syndrome (47,XXY), structural chromosomal abnormalities and Y-chromosomal microdeletions. Consistent with Ohno's law, the human X chromosome is the most stable of all the chromosomes, but contrary to Ohno's law, the X chromosome is loaded with regions of acquired, rapidly evolving genes, which are of special interest because they are predominantly expressed in the testis. Therefore, it is not surprising that the X chromosome, considered as the female counterpart of the male-associated Y chromosome, may actually play an essential role in male infertility and sperm production. This is supported by the recent description of a significantly increased copy number variation (CNV) burden on both sex chromosomes in infertile men and point mutations in X-chromosomal genes responsible for male infertility. Thus, the X chromosome seems to be frequently affected in infertile male patients. Four principal X-chromosomal aberrations have been identified so far: (1) aneuploidy of the X chromosome as found in Klinefelter syndrome (47,XXY or mosaicism for additional X chromosomes). (2) Translocations involving the X chromosome, e.g. nonsyndromic 46,XX testicular disorders of sex development (XX-male syndrome) or X-autosome translocations. (3) CNVs affecting the X chromosome. (4) Point mutations disrupting X-chromosomal genes. All these are reviewed herein and assessed concerning their importance for the clinical routine diagnostic workup of the infertile male as well as their potential to shape research on spermatogenic failure in the next years.

[Genetic aspects of fertility disorders]

Genetic disorders of fertility can occur at the level of gonadal differentiation or function, germ cell production or function, and the genital ducts. In gonadal dysgenesis, the differentiation of testes or ovaries is impaired. Gonadal dysgenesis can be caused by chromosome aberrations or monogenetic defects in XY or XX gonadal dysgenesis. For the biosynthesis of sexual hormones, a normal development of the gonads and an intact hypothalamic-pituitary-gonadal axis is necessary. Disorders of steroid hormone synthesis are associated with an increased or diminished production of sexual hormones. Clinical and genetic aspects of adrenogenital syndrome are discussed here. Mutations of the androgen receptor cause a spectrum of androgen insensitivity ranging from women with female external genitalia through patients with genital ambiguity to men with infertility. Disturbed spermatogenesis is heterogeneous and can be the result of chromosome aberrations such as Klinefelter syndrome or structural aberrations as translocations and microdeletions of the Y chromosome. Premature ovarian failure is characterized by amenorrhea and hypergonadotropic hypogonadism before 40 years of age. Beside nongenetic factors, premature ovarian failure can be caused by chromosome aberrations or monogenetic defects. Disorders of the genital ducts such as anomalies of the müllerian ducts in females and of the wolffian ducts in males can be associated with sterility or infertility.