Mutations and Polymorphisms of the FSH Receptor (FSHR) Gene Clinical Implications in Female Fecundity and Molecular Biology of FSHR Protein and Gene

The portion of chromosome 2, including the gene codifying the receptor of FSH (FSHR gene), can display point mutations that cause variations in the amino acid sequence of the receptor protein (FSHR protein). Some of these structural changes affect the receptor functional properties that may be enhanced (activating mutations) or impaired (inactivating mutations). Activating mutations confer to FSHR a higher responsiveness to FSH, making it constitutively active even in the absence of the ligand, or render it able to nonspecifically respond to other tropic hormones (e.g., TSH). Inactivating mutations reduce the receptor's function up to a total block, altering either the formation of the receptor-ligand complex, or FSH signal transduction. FSHR inactivating mutations may cause primary or secondary amenorrhea, infertility, and premature ovarian failure (POF), whereas activating mutations can predispose to ovarian hyperstimulation syndrome (OHSS) as a consequence of exogenous FSH administration, or with a spontaneous onset. Beside point mutations, FSHR gene polymorphisms at specific sites (e.g., codons 307 and 680) may influence FSHR protein responsiveness to exogenous FSH, and finally affect the effectiveness of in vitro fertilization (IVF) treatment as well as the likelihood of developing a severe OHSS as a consequence of superovulation. This review summarizes the current knowledge about the FSHR gene mutations and polymorphisms, illustrating in the first part their clinical consequences for female reproductive function. In the second part, it describes the techniques to study the FSHR gene sequence, and gives more details about the molecular biology of FSHR protein, of FSHR gene and its mutations.