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OPHN1
oligophrenin 1
OPHN1 is located on the long (q) arm of chromosome X, at band Xq12. Arm ratio per GRCh38 - banding schematic.
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Overview
OPHN1 is located on the X chromosome and encodes oligophrenin-1, a protein essential for establishing and maintaining normal neuronal architecture during brain development. The gene is classified as polygenic in clinical carrier panels, reflecting its role in complex neuropsychiatric phenotypes. The protein regulates the formation and stabilisation of dendritic spines, the tiny protrusions on nerve cells where most excitatory synapses form. Disruption of OPHN1 function can lead to altered brain connectivity, affecting learning, memory, and behaviour. The gene is recognised across multiple NHS Genomic Medicine Service panels for intellectual disability, epilepsy, and cerebellar disorders.
What the gene does
Oligophrenin-1 functions as a regulatory protein controlling the activity of Rho family GTPases, molecular switches that orchestrate the cytoskeleton within nerve cells. The protein's GAP (GTPase-activating protein) activity accelerates the conversion of active, GTP-bound Rho proteins to their inactive GDP-bound state, thereby modulating the actin filaments that give dendritic spines their shape. By fine-tuning these cytoskeletal dynamics, oligophrenin-1 influences spine morphology, synaptic plasticity, and the strength of connections between neurones. The protein also participates in intracellular signalling pathways that govern neuronal migration and differentiation during development. Evidence suggests oligophrenin-1 localises to synapses and interacts with other postsynaptic scaffolding proteins, integrating structural and functional aspects of synaptic transmission. Its regulatory role appears particularly important during critical windows of brain maturation, when neural circuits are refined through experience and activity.
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Chromosome location
OPHN1 resides on the long arm of the X chromosome at band Xq12. The gene spans approximately 340 kilobases of genomic DNA and contains 25 exons that are transcribed and spliced to produce the mature messenger RNA encoding oligophrenin-1. Its X-chromosomal position means that males, who carry only one X chromosome, are more vulnerable to the functional consequences of pathogenic variants, while females may exhibit variable expression depending on X-inactivation patterns. The chromosomal region surrounding OPHN1 contains several other genes involved in neurological development.
Protein structure
Oligophrenin-1 is an 802-amino-acid protein with a modular domain architecture that underlies its regulatory functions. The N-terminal region includes a PH domain (pleckstrin homology domain) spanning amino acids 265-368, which binds phosphoinositide lipids in cell membranes and targets the protein to specific subcellular compartments. The central Rho-GAP domain (amino acids 380-564) catalyses GTPase activation, directly modulating Rho family protein activity. Multiple disordered regions are distributed across the C-terminal half of the protein (amino acids 569-588, 607-666, 680-770, and 783-802), which likely mediate flexible protein-protein interactions and regulatory modifications. This combination of structured catalytic domains and disordered segments allows oligophrenin-1 to integrate diverse cellular signals and respond dynamically to the changing needs of developing synapses.
Key variants
Pathogenic variants in OPHN1 have been identified across the gene's coding sequence, including missense changes that disrupt catalytic activity, nonsense mutations leading to truncated protein, and deletions removing entire exons. Because OPHN1 is X-linked, hemizygous variants in males typically result in more severe phenotypes, while heterozygous females may show milder or variable features depending on patterns of X-chromosome inactivation. The variant spectrum reflects loss of normal protein function, with many changes affecting the critical GAP or PH domains.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1138+1G>A | - | Pathogenic | ★★☆☆ | X-linked intellectual disability-cerebellar hypoplasia syndrome |
c.1246C>T | p.Gln416Ter | Pathogenic | ★★☆☆ | X-linked intellectual disability-cerebellar hypoplasia syndrome |
c.1489C>T | p.Arg497Ter | Pathogenic | ★★☆☆ | X-linked intellectual disability-cerebellar hypoplasia syndrome |
c.1789C>T | p.Arg597Ter | Pathogenic | ★★☆☆ | not provided |
c.468_471del | p.Lys156fs | Pathogenic/Likely pathogenic | ★★☆☆ | Abnormality of the nervous system |
c.1026-2A>G | - | Pathogenic | ★☆☆☆ | X-linked intellectual disability-cerebellar hypoplasia syndrome |
c.2048del | p.Lys683fs | Pathogenic | ★☆☆☆ | X-linked intellectual disability-cerebellar hypoplasia syndrome |
c.568G>T | p.Glu190Ter | Pathogenic | ★☆☆☆ | not provided |
c.813T>A | p.Tyr271Ter | Pathogenic | ★☆☆☆ | X-linked intellectual disability-cerebellar hypoplasia syndrome |
c.826G>T | p.Glu276Ter | Pathogenic | ★☆☆☆ | not provided |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Variants in OPHN1 are primarily associated with neuropsychiatric and neurodevelopmental conditions. The gene features on multiple NHS panels including intellectual disability, early onset or syndromic epilepsy, cerebellar hypoplasia, and hereditary ataxia. Affected individuals may present with cognitive impairment, seizures, delayed motor milestones, and structural brain abnormalities such as cerebellar underdevelopment. The phenotypic spectrum can vary considerably, even within families, reflecting the complexity of brain development and the influence of additional genetic and environmental factors.
No disease links recorded for this gene in our reference set.
UK clinical status
OPHN1 holds green (high-evidence) status on several NHS Genomic Medicine Service panels, reflecting its established role in neurological conditions. It appears on the Intellectual Disability panel (R29), Early Onset or Syndromic Epilepsy panel (R59), Cerebellar Hypoplasia panel, Hereditary Ataxia panel (including the adult-onset ataxia panel, R54), Ataxia and Cerebellar Anomalies narrow panel, DDG2P (Developmental Disorders Genotype-to-Phenotype database), and the Fetal Anomalies panel (R21). This broad representation underscores the gene's relevance across multiple NHS clinical pathways for inherited neurological disorders.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
Why is OPHN1 important for brain development?
Oligophrenin-1 regulates the structural scaffolding of dendritic spines, the primary sites where neurones receive signals from other cells. Proper spine formation is essential for establishing functional neural circuits during development, and disruption of this process can impair learning, memory, and overall cognitive function.
How does the X-chromosomal location of OPHN1 affect inheritance?
Because OPHN1 is on the X chromosome, males with a pathogenic variant typically show more pronounced features, as they have only one copy of the gene. Females with one altered copy may have milder symptoms or be unaffected, depending on which X chromosome is active in different cells throughout the body.
What types of specialists might be involved in managing conditions linked to OPHN1?
Individuals with OPHN1-related conditions often benefit from multidisciplinary care including neurologists, clinical geneticists, developmental paediatricians, epilepsy specialists, and allied health professionals such as speech and occupational therapists. The specific team depends on the individual's presentation and needs.