ABSTRACT: Abstract Cysteine and homocysteine (Hcy), both sulfur?containing amino acids (AAs), produced from methionine another sulfur?containing amino acid, which is converted to Hcy and further converted to cysteine. This article aims to highlight the link between cysteine and Hcy, and their mechanisms, important functions, play in the body and their role as a biomarker for various types of diseases. So that using cysteine and Hcy as a biomarker, we can prevent and diagnose many diseases. This review concluded that hyperhomocysteinemia (elevated levels of homocysteine) is considered as toxic for cells and is associated with different health problems. Hyperhomocysteinemia and low levels of cysteine associated with various diseases like cardiovascular diseases (CVD), ischemic stroke, neurological disorders, diabetes, cancer like lung and colorectal cancer, renal dysfunction?linked conditions, and vitiligo. Cysteine and homocysteine, both sulfur?containing amino acids (AAs) produced from methionine another sulfur?containing amino acid, which is converted to homocysteine and further converted to cysteine. The aim of this article is to highlight the link between cysteine and homocysteine, and their mechanisms, important functions, play in the body and their role as a biomarker for various different types of diseases. Hyperhomocysteinemia (elevated levels of homocysteine) is considered as toxic for cells and is associated with different health problems. Not only hyperhomocysteinemia but also low levels of cysteine in most cases is used as a biomarker for various diseases like cardiovascular diseases (CVD), ischemic stroke, neurological disorders, diabetes, cancer like lung and colorectal cancer, renal dysfunction?linked conditions, and vitiligo.
