Glycyl-tRNA is integral to protein translation and attaches glycine to its cognate RNA.Many different mutations have been found in CMT2D patients and it remains unclear how mutations in GARS1 cause CMT2D. However, it is thought that mutant glycyl-tRNA synthetase (GlyRS) interferes with transmembrane receptors, causing motor disease and that mutations in the gene could disrupt the ability of GlyRS to interact with its cognate RNA, disrupting protein production. The GARS1 mutations present in CMT2D cause a deficient amount of glycyl-tRNA in cells, preventing the elongation phase of protein synthesis. Because elongation is a key step in protein production, ribosomes are unable to continue protein synthesis at glycine sites. GARS1 mutations also stall initiation of translation. Glycine addition failure causes a stress response that further stalls protein production, preventing initiation of translation. By stalling elongation and initiation of translation, CMT2D mutations in the GARS1 gene cause translational repression, meaning that overall translation is inhibited.GARS1-associated axonal neuropathy is progressive, meaning that it worsens over time. Unknown mechanisms are thought to cause the chronic neurodegeneration resulting from the aberrant GlyRS; however, one theory for disease is VEGF-deficiency. Mutant GlysRS interferes with neuronal transmembrane receptors, including neuropilin 1 (Nrp1) and vascular endothelial growth factor (VEGF), causing neuropathy. GARS-CMT2D mutations alter GlyRS and allow it to bind to the Nrp1 receptor, interfering with the normal binding of Nrp1 to VEGF.
The term hypogonadism usually means permanent rather than transient or reversible defects, and usually implies deficiency of reproductive hormones, with or without fertility defects. The term is less commonly used for infertility without hormone deficiency. There are many possible types of hypogonadism and several ways to categorize them. Hypogonadism is also categorized by endocrinologists by the level of the reproductive system that is defective. Physicians measure gonadotropins (LH and FSH) to distinguish primary from secondary hypogonadism. In primary hypogonadism the LH and/or FSH are usually elevated, meaning the problem is in the testicles (hyper-gonatropic hypogonadism); whereas in secondary hypogonadism, both are normal or low, suggesting the problem is in the brain (hypo-gonatropic hypogonadism). Affected system
Hypogonadism resulting from defects of the gonads is referred to as hypergonadotropic hypogonadism or primary hypogonadism. Examples include Klinefelter syndrome and Turner syndrome. Mumps is known to cause testicular failure, and in recent years has been immunized against in the US. A varicocele can reduce hormonal production as well. Hypogonadism resulting from hypothalamic or pituitary defects is termed hypogonadotropic hypogonadism (HH), secondary hypogonadism, or central hypogonadism (referring to the central nervous system).Examples of hypothalamic defects include Kallmann syndrome. Examples of pituitary defects include hypopituitarism and pituitary hypoplasia. An example of a hypogonadism resulting from the lack of hormone response is androgen insensitivity syndrome, where there are inadequate receptors to bind the testosterone, resulting in varying clinical phenotypes of sexual characteristics despite XY chromosomes.