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RPS6KA3
ribosomal protein S6 kinase A3
RPS6KA3 is located on the short (p) arm of chromosome X, at band Xp22.12. Arm ratio per GRCh38 - banding schematic.
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Overview
RPS6KA3 is located on the X chromosome and encodes ribosomal protein S6 kinase A3, also known as RSK2. This enzyme belongs to a family of serine/threonine kinases that act as molecular switches in cellular signalling pathways. The protein coordinates responses to extracellular signals by phosphorylating downstream targets, thereby influencing gene expression and cellular behaviour.
The RPS6KA3 protein is particularly abundant in brain tissue, where it participates in synaptic plasticity - the ability of connections between nerve cells to strengthen or weaken over time. Research suggests this function is essential for converting short-term experiences into stable, long-term memories. Pathogenic variants in RPS6KA3 eliminate or severely reduce the protein's enzymatic activity, leading to neurological and skeletal manifestations.
What the gene does
RPS6KA3 encodes a dual-kinase enzyme that integrates signals from growth factors and other external stimuli into changes in cellular behaviour. The protein functions as part of the mitogen-activated protein kinase (MAPK) signalling cascade, where it acts as a downstream effector that phosphorylates numerous substrate proteins. These phosphorylation events regulate diverse processes including cell proliferation, differentiation, and survival decisions.
In neurons, the RPS6KA3 protein contributes to activity-dependent synaptic modifications that underpin learning and memory. Evidence suggests the kinase phosphorylates transcription factors and chromatin-modifying proteins, thereby altering gene expression programmes in response to neuronal activity. This molecular function connects immediate electrical events at synapses to longer-lasting structural and functional changes in neural circuits. The protein also appears to support nerve cell survival by modulating apoptotic pathways, though the precise mechanisms remain under investigation.
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Chromosome location
RPS6KA3 is located on the short arm of the X chromosome at position p22.12. This chromosomal region contains numerous genes, and its proximity to the centromere means it lies within a gene-dense area of the X chromosome. The genomic organisation of RPS6KA3 spans a substantial stretch of DNA, with the coding sequence distributed across multiple exons that undergo splicing to produce the mature messenger RNA.
Protein structure
The RPS6KA3 protein comprises 740 amino acids organised into functionally distinct domains. The N-terminal region begins with a Disordered segment spanning amino acids 1-38, which likely provides flexibility for protein-protein interactions. This is followed by Protein kinase 1, a catalytic domain extending from amino acids 68-327 that carries out phosphorylation reactions. An AGC-kinase C-terminal domain occupies positions 328-397, characteristic of the AGC kinase superfamily to which RPS6KA3 belongs. The protein contains a second catalytic region, Protein kinase 2, located at amino acids 422-679. This dual-kinase architecture allows the protein to integrate multiple signalling inputs and phosphorylate diverse substrate proteins with different sequence preferences.
Key variants
More than 125 pathogenic variants in RPS6KA3 have been documented in clinical databases, encompassing missense substitutions, nonsense changes, frameshift insertions and deletions, and splice-site alterations. These variants typically eliminate kinase activity or prevent production of functional protein. Because RPS6KA3 resides on the X chromosome, males carrying a single pathogenic variant generally display more severe manifestations than females, who possess a second X chromosome copy that may partially compensate.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Pathogenic variants in RPS6KA3 cause Coffin-Lowry syndrome, a rare X-linked condition characterised by intellectual disability, distinctive facial features, skeletal abnormalities, and progressive neurological complications. Affected males typically show moderate to severe cognitive impairment, while carrier females may exhibit milder learning difficulties. Some individuals with RPS6KA3 variants present with intellectual disability without the full spectrum of Coffin-Lowry syndrome features, a presentation sometimes described as X-linked intellectual disability. The phenotypic variability likely reflects the specific location and effect of each variant on protein function, as well as modifying genetic and environmental factors.
UK clinical status
RPS6KA3 appears on multiple NHS Genomic Medicine Service gene panels with green (definitive) evidence ratings. The gene is included in the DDG2P developmental disorders resource and features in specialist panels for Fetal anomalies (R21), Hydrocephalus (R86), Intellectual disability (R29), and IUGR and IGF abnormalities. These panel memberships reflect the established role of RPS6KA3 variants in causing recognisable neurodevelopmental and skeletal phenotypes that may be identified through prenatal imaging or postnatal clinical assessment.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
Why are males more severely affected by RPS6KA3 variants than females?
RPS6KA3 is located on the X chromosome. Males have only one X chromosome, so a single pathogenic variant eliminates RPS6KA3 function entirely. Females possess two X chromosomes, and the unaffected copy often provides partial compensation, resulting in milder or absent symptoms.
Can RPS6KA3 variants be detected through standard genetic testing?
Yes, RPS6KA3 variants can be identified through chromosomal microarray, exome sequencing, or targeted gene panels for intellectual disability and developmental disorders. The gene's inclusion on multiple NHS panels means testing is available through clinical genetics services when the phenotype suggests Coffin-Lowry syndrome or related presentations.
Do all RPS6KA3 variants cause Coffin-Lowry syndrome?
Most loss-of-function variants cause the full Coffin-Lowry syndrome spectrum in affected males, but some individuals present with isolated intellectual disability without prominent skeletal features. The relationship between specific variants and clinical presentation remains an area of ongoing research.
References
- Raymond FL. X linked mental retardation: a clinical guide. Journal of medical genetics. 2006. PMID: 16118346
- Delaunoy JP, Dubos A, Marques Pereira P. Identification of novel mutations in the RSK2 gene (RPS6KA3) in patients with Coffin-Lowry syndrome. Clinical genetics. 2006. PMID: 16879200
- Field M, Tarpey P, Boyle J. Mutations in the RSK2(RPS6KA3) gene cause Coffin-Lowry syndrome and nonsyndromic X-linked mental retardation. Clinical genetics. 2006. PMID: 17100996
- Guimiot F, Delezoide AL, Hanauer A. Expression of the RSK2 gene during early human development. Gene expression patterns : GEP. 2004. PMID: 14678837
- Zeniou M, Gattoni R, Hanauer A. Delineation of the mechanisms of aberrant splicing caused by two unusual intronic mutations in the RSK2 gene involved in Coffin-Lowry syndrome. Nucleic acids research. 2004. PMID: 14973203
- Hanauer A, Young ID. Coffin-Lowry syndrome: clinical and molecular features. Journal of medical genetics. 2002. PMID: 12362025
- Zeniou M, Ding T, Trivier E. Expression analysis of RSK gene family members: the RSK2 gene, mutated in Coffin-Lowry syndrome, is prominently expressed in brain structures essential for cognitive function and learning. Human molecular genetics. 2002. PMID: 12393804
- Delaunoy J, Abidi F, Zeniou M. Mutations in the X-linked RSK2 gene (RPS6KA3) in patients with Coffin-Lowry syndrome. Human mutation. 2001. PMID: 11180593