Genetics
Coffin–Lowry syndrome is an X-linked disorder resulting from loss-of-function mutations in the RPS6KA3 gene, which encodes RSK2 (ribosomal S6 kinase 2). Multiple mutations have been identified in RPS6KA3 that can give rise to the disorder, including missense mutations, nonsense mutations, insertions and deletions. Individuals with CLS rarely have affected parents, suggesting that most incidents arise from de novo mutations in the germline. The lack of an inheritance pattern may be due to the fact that affected individuals are unlikely to parent children. In 20–30% of cases, however, there is a family history of disease. In these cases, the disorder is typically inherited from the maternal parent. Because RPS6KA3 is located on the X chromosome, males (who possess only one copy of the X chromosome) display more severe symptoms than females. Affected females usually possess one mutated copy of the RPS6KA3 gene and one wild type copy. Random inactivation of one copy of the X chromosome in females mitigates the impact of possessing a mutant allele. Occasionally females are born with two mutated alleles. In these cases the symptoms are as severe as in males with the disease. Cell physiology
Mutations in the RPS6KA3 gene can result in expression of an RSK2 protein (ribosomal S6 kinase 2) with reduced or absent kinase function. RSK2 is a downstream component of the MAPK (mitogen-activated protein kinase) cascade that is itself a kinase. RSK2 phosphorylates cellular proteins (including histone H3, and CREB), which regulate eukaryotic gene expression.
Azacitidine, sold under the brand name Vidaza among others, is used for the treatment of myelodysplastic syndrome, myeloid leukemia, and juvenile myelomonocytic leukemia. It is a chemical analog of cytidine, a nucleoside in DNA and RNA. Azacitidine and its deoxy derivative, decitabine (also known as 5-aza-2′-deoxycytidine) were first synthesized in Czechoslovakia as potential chemotherapeutic agents for cancer.The most common adverse reactions in children with juvenile myelomonocytic leukemia include pyrexia, rash, upper respiratory tract infection, and anemia. Medical uses
Azacitidine is indicated for the treatment of myelodysplastic syndrome, for which it received approval by the U.S. Food and Drug Administration (FDA) on May 19, 2004. In two randomized controlled trials comparing azacitidine to supportive treatment, 16% of subjects with myelodysplastic syndrome who were randomized to receive azacitidine had a complete or partial normalization of blood cell counts and bone marrow morphology, compared to none who received supportive care, and about two-thirds of patients who required blood transfusions no longer needed them after receiving azacitidine.Azacitidine is also indicated for the treatment of myeloid leukemia and juvenile myelomonocytic leukemia. Mechanism of action
Azacitidine is a chemical analogue of the nucleoside cytidine, which is present in DNA and RNA. It is thought to have antineoplastic activity via two mechanisms – at low doses, by inhibiting of DNA methyltransferase, causing hypomethylation of DNA, and at high doses, by its direct cytotoxicity to abnormal hematopoietic cells in the bone marrow through its incorporation into DNA and RNA, resulting in cell death.