There are two major pathways of deficiency of CoQ in humans: reduced biosynthesis, and increased use by the body. Biosynthesis is the major source of CoQ. Biosynthesis requires at least 15 genes, and mutations in any of them can cause CoQ deficiency. CoQ levels also may be affected by other genetic defects (such as mutations of mitochondrial DNA, ETFDH, APTX, FXN, and BRAF, genes that are not directly related to the CoQ biosynthetic process). Some of these, such as mutations in COQ6, can lead to serious diseases such as steroid-resistant nephrotic syndrome with sensorineural deafness.