MDDS is associated with mutations in the genes TK2, SUCLA2, RRM2B, DGUOK, POLG, TYMP, SUCLG1,  and TWNK.Myopathic MDS is strongly correlated to a variety of mutations in the gene TK2, seeing a reduction of TK2 activity to less than 32% in people with MDS found with the mutation. Because TK2 plays a key role in the mitochondrial salvage pathways of several deoxyribonucleoside triphosphates (dNTPs), a lowered activity would lead to less cycling of nucleotides. This lack of nucleotide recycling is detrimental since the mitochondria cannot synthesize entirely new deoxynucleotides, and the inner membrane of the mitochondria prevents the negatively charged nucleotides of the cytosol from entering.The SUCLA2 gene codes for the beta-subunit of SCS-A. This enzyme catalyzes the synthesis of succinate and coenzyme A into succinyl-CoA, but is also associated with the complex formed by nucleoside diphosphate kinase (NDPK) in the last step of the dNTP salvage pathway.The RRM2B gene, which is expressed in the cell nucleus, codes for one of two versions of the R2 subunit of ribonucleotide reductase, which generates nucleotide precursors required for DNA replication by reducing ribonucleoside diphosphates to deoxyribonucleoside diphosphates. The version of R2 encoded by RRM2B is induced by TP53, and is required for normal DNA repair and mtDNA synthesis in non-proliferating cells. The other form of R2 is expressed only in dividing cells.The DGUOK gene encodes for mitochondrial deoxyguanosine kinase (dGK), which catalyzes the phosphorylation of deoxyribonucleosides into nucleotides.
Hypocalciuria is a low level of calcium in the urine. It is a significant risk factor for predicting eclampsia in pregnancy. The most common causes for hypocalciuria is either thiazide diuretics or reduced dietary intake of calcium. The other cause is Familial hypocalciuric hypercalcemia (FHH). Low dietary sodium causes hypocalciuria. It is also common in patients with Gitelman syndrome. == References ==