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PDE6G
phosphodiesterase 6G
PDE6G is located on the long (q) arm of chromosome 17, at band 17q25.3. Arm ratio per GRCh38 - banding schematic.
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Overview
PDE6G encodes the gamma subunit of rod cyclic GMP phosphodiesterase (PDE6), a multi-subunit enzyme that plays a central role in vision. This protein acts as an inhibitory regulator, controlling the activity of the catalytic subunits of the phosphodiesterase complex in rod photoreceptor cells. Rod cells are specialised retinal neurons responsible for vision in dim light conditions.
When functioning normally, the PDE6G protein helps ensure that the phototransduction cascade - the process by which light is converted into electrical signals in the retina - operates efficiently. Pathogenic variants in PDE6G can impair this regulatory function, leading to progressive retinal degeneration. The gene is clinically significant in ophthalmology, particularly in the diagnosis and management of inherited retinal disorders.
What the gene does
The PDE6G protein serves as the inhibitory gamma subunit of rod photoreceptor phosphodiesterase, a heterotetrameric enzyme composed of two catalytic subunits and two gamma regulatory subunits. In darkness, the gamma subunits bind tightly to the catalytic subunits, preventing them from breaking down cyclic GMP (cGMP). This maintained level of cGMP keeps ion channels in the photoreceptor membrane open, allowing an influx of calcium and sodium ions.
When light strikes the retina, it triggers a cascade of molecular events. The activated visual pigment rhodopsin stimulates a G protein called transducin, which in turn causes the gamma subunits to release from the catalytic core of PDE6. This release allows the catalytic subunits to rapidly hydrolyse cGMP, causing ion channels to close and the photoreceptor cell to hyperpolarise, generating an electrical signal that is transmitted to the brain. The gamma subunit's inhibitory function is therefore essential for maintaining the dynamic range of the phototransduction system and for rapid adaptation to changing light conditions.
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Chromosome location
PDE6G is located on the long arm of chromosome 17 at position 25.3 (17q25.3). This chromosomal region lies near the telomere of chromosome 17. The gene spans a relatively compact genomic region and encodes a small protein of 87 amino acids, reflecting its specialised regulatory role within the photoreceptor phosphodiesterase complex.
Protein structure
The PDE6G protein is composed of 87 amino acids, making it one of the smaller regulatory proteins in the phototransduction pathway. A disordered region extends from amino acids 1 to 55, encompassing the majority of the protein. Intrinsically disordered regions in regulatory proteins often facilitate flexible binding interactions with partner proteins, allowing the gamma subunit to engage with and inhibit the catalytic core of the phosphodiesterase complex. The C-terminal portion of the protein is thought to contain key residues that mediate high-affinity binding to the catalytic subunits, though the precise structural determinants of inhibition remain an area of active investigation.
Key variants
Pathogenic variants in PDE6G typically follow an autosomal recessive inheritance pattern, meaning that affected individuals carry two altered copies of the gene. Loss-of-function variants that reduce or eliminate gamma subunit function can lead to uncontrolled phosphodiesterase activity, resulting in abnormally low cGMP levels and progressive degeneration of rod photoreceptors. The variant spectrum includes missense changes that disrupt binding to the catalytic subunits, as well as nonsense and frameshift variants that produce truncated, non-functional proteins.
Sample of pathogenic variants
4 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.146+1G>T | - | Pathogenic | ★☆☆☆ | Retinal dystrophy |
c.187+1G>T | - | Pathogenic | ★☆☆☆ | PDE6G-related disorders |
c.69dup | p.Arg24fs | Pathogenic | ★☆☆☆ | not provided |
c.97C>T | p.Arg33Ter | 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
Pathogenic variants in PDE6G are associated with autosomal recessive retinitis pigmentosa, a group of inherited retinal dystrophies characterised by progressive vision loss. Individuals with PDE6G-related retinitis pigmentosa typically experience night blindness in early childhood or adolescence, reflecting the loss of rod photoreceptor function. Over time, the degeneration may extend to cone photoreceptors, leading to tunnel vision and eventual loss of central vision. The severity and rate of progression can vary among affected individuals, even within families carrying the same pathogenic variants.
No disease links recorded for this gene in our reference set.
UK clinical status
PDE6G appears on multiple NHS Genomic Medicine Service gene panels, reflecting its clinical relevance for genetic testing in the UK. The gene holds green (high evidence) classification on the DDG2P panel for developmental disorders with genomic imbalance. It is also included in the Retinal disorders panel with green classification (R32 evidence level), indicating strong evidence for its role in inherited retinal disease. These panel memberships mean that PDE6G variants are routinely assessed in NHS diagnostic testing for patients presenting with retinal degeneration and related phenotypes.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the role of PDE6G in vision?
PDE6G encodes a regulatory subunit that controls the activity of rod photoreceptor phosphodiesterase, an enzyme critical for converting light signals into electrical signals in the retina. The protein acts as an inhibitor that is released during light exposure, allowing the enzyme to break down cyclic GMP and generate a visual signal.
How are PDE6G variants inherited?
Pathogenic variants in PDE6G typically follow an autosomal recessive pattern of inheritance. This means an individual must inherit two altered copies of the gene - one from each parent - to develop retinal disease. Parents who each carry one pathogenic variant are usually unaffected carriers.
What symptoms are associated with PDE6G-related retinal conditions?
Individuals with PDE6G-related retinitis pigmentosa often experience night blindness as an early symptom, reflecting the loss of rod photoreceptor function. Progressive vision loss, tunnel vision, and eventual loss of central vision may develop over time as the retinal degeneration advances.