GUCY2D-Related Retinopathy

1. Disease Information

Overview

GUCY2D-related retinopathy is an umbrella term for inherited retinal dystrophies caused by pathogenic variants in the GUCY2D gene, which encodes retinal guanylate cyclase-1 (RetGC-1), an enzyme critical for cyclic GMP (cGMP) synthesis in photoreceptor cells (varela2022lebercongenitalamaurosisearlyonset pages 3-3, wong2025monogenicretinaldiseases pages 8-9). The disease manifests as two principal phenotypes depending on the inheritance pattern and type of mutation: (1) Leber congenital amaurosis type 1 (LCA1), a severe congenital or early-onset retinal dystrophy caused by biallelic loss-of-function variants (autosomal recessive), and (2) Cone-rod dystrophy type 6 (CORD6), a progressive cone-dominant degeneration caused by heterozygous gain-of-function variants (autosomal dominant) (gao2023phenotypiccharacterizationof pages 1-2, bouzia2020gucy2dassociatedlebercongenital pages 1-5, li2023cgmpsignalingin pages 4-5). GUCY2D mutations account for approximately 6–21% of all LCA cases and up to 25–40% of autosomal dominant cone-rod dystrophy cases worldwide (gong2024infantilenystagmussyndrome—associated pages 4-5, hahn2022thenaturalhistory pages 1-2).

Key Identifiers

The following table summarizes the core disease identifiers and nomenclature for GUCY2D-related retinopathy:

Table: This table compiles the core identifiers and nomenclature needed to index GUCY2D-related retinopathy in a disease knowledge base. It links the gene, major phenotype-specific disease entries, ontology terms, and inheritance patterns supported by the retrieved evidence.

Common Synonyms

• GUCY2D-LCA, LCA1, GUCY2D-associated Leber congenital amaurosis (bouzia2020gucy2dassociatedlebercongenital pages 1-5, NCT03920007 chunk 1)
• CORD6, GUCY2D-associated cone-rod dystrophy (OpenTargets Search: -GUCY2D, hahn2022thenaturalhistory pages 1-2)
• RetGC-1 deficiency (recessive form)
• GUCY2D-related recessive retinopathy (MONDO_0100453) (OpenTargets Search: -GUCY2D)
• Early-onset severe retinal dystrophy (EOSRD) when onset is after infancy but before age 5 (bouzia2020gucy2dassociatedlebercongenital pages 1-5)

Information Sources

Information is derived from aggregated disease-level resources including OMIM, Orphanet, ClinVar, OpenTargets, and published cohort studies from tertiary referral centers.

2. Etiology

Disease Causal Factors

GUCY2D-related retinopathy is a purely monogenic (Mendelian) disorder. The primary cause is pathogenic variation in the GUCY2D gene located on chromosome 17p13.1 (huang2021leber’scongenitalamaurosis pages 5-6). The gene encodes retinal guanylate cyclase-1 (RetGC-1/GC-E), which synthesizes cGMP—the intracellular second messenger essential for photoreceptor excitation and recovery during phototransduction (varela2022lebercongenitalamaurosisearlyonset pages 3-3, wong2025monogenicretinaldiseases pages 8-9).

Genetic Risk Factors

• Biallelic (homozygous or compound heterozygous) loss-of-function variants in GUCY2D cause autosomal recessive LCA1/EOSRD. Null alleles (frameshift, nonsense, splice-site variants) account for approximately 88% of LCA-causing alleles (varela2022lebercongenitalamaurosisearlyonset pages 3-3).
• Heterozygous gain-of-function missense variants, particularly at codon 838 in exon 13, cause autosomal dominant CORD6. The most common CORD variant is c.2513G>A (p.Arg838His), found in 54.4% of CORD patients in one large cohort (hahn2022thenaturalhistory pages 5-7).
• Consanguinity plays a notable role, particularly in populations with high rates of consanguineous marriage; one Indian cohort reported consanguinity in 54% of LCA families (huang2021leber’scongenitalamaurosis pages 5-6).

Environmental and Protective Factors

No environmental risk factors, protective factors, or gene-environment interactions have been identified for this purely genetic disorder. Disease expression is determined by the specific GUCY2D genotype.

Modifier Genes

Potential modifier genes have been explored in familial studies. One investigation identified variants in CACNG8, PAX2, RXRG, CCDC175, PDE4DIP, and LTF as candidate modifiers that may contribute to intrafamilial phenotypic heterogeneity in GUCY2D-associated CORD (donato2022theimpactof pages 7-10).

3. Phenotypes

The phenotypic spectrum of GUCY2D-related retinopathy is summarized in the following table:

Table: This table summarizes major phenotypes reported across GUCY2D-related recessive retinopathy/LCA1 and dominant CORD6, with suggested HPO mappings, onset patterns, and qualitative frequency information. It is useful for disease knowledge base curation and phenotype annotation.

LCA1 Phenotype (Recessive)

Patients with GUCY2D-LCA present within the first year to three years of life with severe visual impairment, nystagmus, oculodigital sign (Franceschetti sign), and prominent photophobia (bouzia2020gucy2dassociatedlebercongenital pages 1-5, huang2021leber’scongenitalamaurosis pages 5-6, bouzia2020gucy2dassociatedlebercongenital pages 8-10). Approximately 50% of patients have vision worse than counting fingers, and only about 25% achieve measurable Snellen visual acuity (huang2021leber’scongenitalamaurosis pages 5-6). Full-field electroretinography (ERG) shows severely reduced or extinguished responses affecting both rod and cone pathways (bouzia2020gucy2dassociatedlebercongenital pages 10-14, bouzia2020gucy2dassociatedlebercongenital pages 8-10). Hyperopia is the most common refractive error (gong2024infantilenystagmussyndrome—associated pages 4-5, huang2021leber’scongenitalamaurosis pages 1-2). A distinctive and diagnostically important feature of GUCY2D-LCA is a dissociation between retinal structure and function: optical coherence tomography (OCT) often reveals preserved ellipsoid zone (EZ) and relatively intact outer nuclear layer (ONL) centrally, despite profoundly reduced visual function (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 10-14). Complications include keratoconus and early-onset cataracts in some patients (bouzia2020gucy2dassociatedlebercongenital pages 8-10).

CORD6 Phenotype (Dominant)

GUCY2D-associated CORD typically presents during childhood or adolescence with progressive loss of visual acuity, color vision defects (dyschromatopsia), photophobia, and central scotomas (gao2023phenotypiccharacterizationof pages 1-2, donato2022theimpactof pages 7-10, hahn2022thenaturalhistory pages 1-2). ERG shows reduced cone responses with relatively preserved rod responses early in the disease, with subsequent rod involvement (gao2023phenotypiccharacterizationof pages 1-2, donato2022theimpactof pages 7-10). Fundus examination reveals early granular retinal pigment epithelium (RPE) abnormalities progressing to macular atrophy in older patients (gao2023phenotypiccharacterizationof pages 1-2, gao2023phenotypiccharacterizationof pages 7-8). OCT demonstrates reduced retinal thickness, loss of outer retinal bands, and progressive retinal atrophy (gao2023phenotypiccharacterizationof pages 1-2, donato2022theimpactof pages 7-10).

Quality of Life Impact

Both phenotypes cause significant impact on daily functioning. LCA1 patients experience profound lifelong visual disability typically from infancy, while CORD6 patients face progressive visual decline culminating in severe visual impairment during mid-to-late adulthood (hahn2022thenaturalhistory pages 1-2, bouzia2020gucy2dassociatedlebercongenital pages 5-8).

4. Genetic/Molecular Information

Causal Gene

GUCY2D (guanylate cyclase 2D, retinal) - HGNC symbol: GUCY2D - OMIM gene: 600179 - Ensembl: ENSG00000132518 - Chromosomal location: 17p13.1 (OpenTargets Search: -GUCY2D, huang2021leber’scongenitalamaurosis pages 5-6) - Protein product: Retinal guanylate cyclase-1 (RetGC-1/GC-E)

RetGC-1 is responsible for over 70% of cGMP production in photoreceptors and is expressed in both rod and cone outer segments, with higher expression in cones (huang2021leber’scongenitalamaurosis pages 5-6, li2023cgmpsignalingin pages 2-4). Its activity is regulated by guanylate cyclase activating proteins (GCAPs) in a calcium-dependent manner (li2023cgmpsignalingin pages 2-4).

Pathogenic Variants

Over 248 variants in GUCY2D have been identified as causing autosomal recessive LCA/EOSRD, while approximately 30 variants are linked to autosomal dominant CORD (gong2024infantilenystagmussyndrome—associated pages 4-5). In one large natural history study of LCA patients, variant types included: missense (71.4%), nonsense (31.4%), and frameshift (7.1%) mutations (hahn2022thenaturalhistory pages 5-7). Additional variant types include in-frame deletions and splice-site variants (bouzia2020gucy2dassociatedlebercongenital pages 16-20).

Notable recessive (LCA1) variants include: - c.1694T>C (p.Phe565Ser)—recurrent in LCA cohorts (hahn2022thenaturalhistory pages 5-7) - c.2302C>T (p.Arg768Trp)—found in compound heterozygotes (hahn2022thenaturalhistory pages 5-7, areblom2023adescriptionof pages 9-10) - c.1343C>A (p.Ser448*)—nonsense variant (bouzia2020gucy2dassociatedlebercongenital pages 16-20) - c.901_908delCTTCGCAG—frameshift variant (bouzia2020gucy2dassociatedlebercongenital pages 16-20)

Notable dominant (CORD6) variants: - c.2513G>A (p.Arg838His)—most common CORD variant, found in 54.4% of patients in one cohort (hahn2022thenaturalhistory pages 5-7) - c.2512C>T (p.Arg838Cys)—recurrent CORD variant (gao2023phenotypiccharacterizationof pages 1-2) - c.2513G>C (p.Arg838Pro)—identified as a causative CORD variant (donato2022theimpactof pages 10-11)

Functional Consequences

• Loss-of-function (recessive): Null or severely damaging alleles abolish or markedly reduce RetGC-1 catalytic activity, impairing cGMP resynthesis after phototransduction. Complete loss of RetGC-1 catalytic ability consistently results in congenital blindness (wong2025monogenicretinaldiseases pages 8-9, li2023cgmpsignalingin pages 4-5, li2023cgmpsignalingin pages 13-14).
• Gain-of-function (dominant): Missense variants at codon 838 alter the calcium sensitivity of RetGC-1, making the enzyme abnormally active or excessively sensitive to GCAP regulation. This produces elevated cGMP levels that keep CNG channels constitutively open, increasing Na⁺ and Ca²⁺ influx and triggering apoptotic photoreceptor death (wong2025monogenicretinaldiseases pages 8-9, li2023cgmpsignalingin pages 4-5).

Genotype-Phenotype Correlations

Variants in exon 2 (extracellular domain) of GUCY2D are associated with milder LCA phenotypes and better-preserved visual acuity over time (bouzia2020gucy2dassociatedlebercongenital pages 10-14). For CORD, variants cluster predominantly at codon 838 in exon 13, with up to 87% of CORD patients carrying the two most prevalent variants at this position (hahn2022thenaturalhistory pages 5-7, hahn2022thenaturalhistory pages 1-2).

RD3 as a Related Gene

RD3 (RD3 regulator of GUCY2D; OMIM gene for RD3) is a protein that regulates GUCY2D trafficking and function. Mutations in RD3 can also cause LCA, mechanistically linked through RetGC-1 dysfunction (OpenTargets Search: -GUCY2D).

5. Environmental Information

GUCY2D-related retinopathy is a purely genetic disorder with no known environmental, lifestyle, or infectious contributing factors. No environmental or lifestyle modifications have been identified that alter disease risk or progression.

6. Mechanism / Pathophysiology

The pathophysiology of GUCY2D-related retinopathy is comprehensively compared between the two major disease mechanisms in the following table:

Table: This table compares the two major molecular mechanisms of GUCY2D-related retinopathy: recessive loss-of-function causing LCA1 and dominant gain-of-function causing CORD6. It is useful for linking genotype to biochemical dysfunction, retinal physiology, and clinical phenotype.

Molecular Pathways

RetGC-1 is a central enzyme in the phototransduction recovery cascade. In normal photoreceptors, light activation triggers a signaling cascade (rhodopsin → transducin → phosphodiesterase 6) that hydrolyzes cGMP, causing CNG channel closure and hyperpolarization. During recovery, RetGC-1 resynthesizes cGMP under GCAP-mediated calcium regulation, reopening CNG channels and restoring the dark state (wong2025monogenicretinaldiseases pages 8-9, li2023cgmpsignalingin pages 2-4).

Loss-of-Function Mechanism (LCA1)

When RetGC-1 is absent or catalytically impaired, cGMP cannot be regenerated after light-induced hydrolysis. CNG channels fail to reopen, and photoreceptors remain in a permanently hyperpolarized, functionally silent state. Despite this severe functional deficit, photoreceptor cells may remain structurally intact for prolonged periods—a phenomenon termed "structure-function dissociation"—because the cells are not actively dying but rather dysfunctional (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 10-14, li2023cgmpsignalingin pages 13-14).

Gain-of-Function Mechanism (CORD6)

Dominant mutations alter the calcium-sensitivity of RetGC-1 regulation by GCAPs, causing the enzyme to remain excessively active even at normal or elevated intracellular calcium levels. This results in pathological cGMP accumulation, persistent opening of CNG channels, excessive Na⁺/Ca²⁺ influx, and activation of downstream death pathways including cGMP/PKG signaling, endoplasmic reticulum stress, calpain activation, and Ca²⁺-mediated apoptosis (wong2025monogenicretinaldiseases pages 8-9, li2023cgmpsignalingin pages 4-5, li2023cgmpsignalingin pages 11-13).

Relevant Ontology Terms

• GO Biological Processes: GO:0007602 (phototransduction); GO:0006171 (cGMP biosynthetic process); GO:0007601 (visual perception); GO:0006816 (calcium ion transport); GO:0097190 (apoptotic signaling pathway)
• GO Cellular Component: GO:0001750 (photoreceptor outer segment)
• Cell types (CL): CL:0000604 (retinal rod cell); CL:0000573 (retinal cone cell); CL:0002586 (retinal pigment epithelial cell)
• KEGG/Reactome: Phototransduction cascade; Visual cycle; cGMP-PKG signaling pathway

7. Anatomical Structures Affected

Organ Level

• Primary: Eye (retina)—specifically the neurosensory retina containing photoreceptor cells
• Body system: Nervous system (visual pathway)
• UBERON: UBERON:0000966 (retina); UBERON:0000019 (camera-type eye)

Tissue and Cell Level

• Photoreceptor outer segments: Primary site of RetGC-1 expression and cGMP synthesis (huang2021leber’scongenitalamaurosis pages 5-6, li2023cgmpsignalingin pages 2-4)
• Cone photoreceptors (CL:0000573): Preferentially affected in CORD6; RetGC-1 is expressed at higher levels in cones (huang2021leber’scongenitalamaurosis pages 5-6, wong2025monogenicretinaldiseases pages 8-9)
• Rod photoreceptors (CL:0000604): Also affected in LCA1 (both rods and cones dysfunctional); secondary involvement in advanced CORD6
• Retinal pigment epithelium (CL:0002586): Secondary changes including RPE mottling and atrophy (bouzia2020gucy2dassociatedlebercongenital pages 14-16, donato2022theimpactof pages 7-10)
• Macula (UBERON:0000053): Central macular structure particularly important in disease; preserved centrally in early LCA1 but progressively atrophied in CORD6

Subcellular Level

• Photoreceptor outer segment disc membranes (site of RetGC-1 localization)
• CNG channels on outer segment plasma membrane
• GO Cellular Component: GO:0001750 (photoreceptor outer segment)

8. Temporal Development

Onset

LCA1 (Recessive): Congenital or early infantile onset, typically within the first year of life. All patients in one cohort developed nystagmus and marked visual acuity reduction within the first three years (bouzia2020gucy2dassociatedlebercongenital pages 1-5, bouzia2020gucy2dassociatedlebercongenital pages 8-10). The onset pattern is congenital/insidious with severe visual impairment apparent from birth or early infancy.

CORD6 (Dominant): Childhood to adolescent onset, typically around the second decade of life, with progressive decline thereafter (hahn2022thenaturalhistory pages 1-2). The onset is subacute to insidious with gradual deterioration of central and color vision.

Progression

LCA1: Despite severe congenital impairment, the disease course is relatively stable in most patients. Serial ERG recordings show lack of deterioration, and OCT imaging demonstrates minimal structural progression over follow-up periods of 2–13.3 years (bouzia2020gucy2dassociatedlebercongenital pages 10-14, bouzia2020gucy2dassociatedlebercongenital pages 8-10). However, some patients experience additional visual decline due to complications such as keratoconus or early-onset cataracts (bouzia2020gucy2dassociatedlebercongenital pages 8-10).

CORD6: Clearly progressive disease with annual BCVA worsening of approximately 0.022 logMAR per year. There is a 32% probability of blindness or severe visual impairment by age 40 (hahn2022thenaturalhistory pages 1-2). Structural degeneration on imaging becomes more apparent over time with progressive macular atrophy (gao2023phenotypiccharacterizationof pages 1-2, gao2023phenotypiccharacterizationof pages 7-8).

Disease Duration

Both phenotypes represent chronic, lifelong conditions. LCA1 is a congenital disease with lifelong severe visual impairment. CORD6 is a progressive degenerative disease culminating in severe visual impairment during mid-to-late adulthood (hahn2022thenaturalhistory pages 1-2).

9. Inheritance and Population

Inheritance Patterns

• Autosomal recessive (AR): LCA1/EOSRD, caused by biallelic loss-of-function GUCY2D variants (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 1-5)
• Autosomal dominant (AD): CORD6/cone dystrophy, caused by heterozygous gain-of-function variants (gao2023phenotypiccharacterizationof pages 1-2, wong2025monogenicretinaldiseases pages 8-9)

Epidemiology

LCA as a group has an estimated prevalence of approximately 1:33,000–80,000 births and is responsible for approximately 20% of childhood blindness (varela2022lebercongenitalamaurosisearlyonset pages 3-3). GUCY2D variants account for 6–21% of all LCA cases, making it one of the most commonly affected genes (varela2022lebercongenitalamaurosisearlyonset pages 3-3, huang2021leber’scongenitalamaurosis pages 5-6, gong2024infantilenystagmussyndrome—associated pages 4-5, hahn2022thenaturalhistory pages 1-2). In an Indian cohort, GUCY2D was the most common causative gene at 20% of cases (huang2021leber’scongenitalamaurosis pages 5-6). GUCY2D accounts for up to 25–40% of all autosomal dominant cone-rod dystrophy cases (wong2025monogenicretinaldiseases pages 8-9, gong2024infantilenystagmussyndrome—associated pages 4-5, hahn2022thenaturalhistory pages 1-2).

Population Demographics

• Autosomal recessive inheritance is seen in approximately 94% of LCA cases (huang2021leber’scongenitalamaurosis pages 5-6)
• No specific ethnic predisposition has been definitively established, though consanguinity significantly increases the risk of autosomal recessive forms
• The sex ratio is approximately equal (huang2021leber’scongenitalamaurosis pages 5-6)

10. Diagnostics

Clinical Tests

Electroretinography (ERG): The gold-standard functional test. In LCA1, full-field ERG shows severely reduced or undetectable dark-adapted (scotopic) and light-adapted (photopic) responses (bouzia2020gucy2dassociatedlebercongenital pages 10-14, bouzia2020gucy2dassociatedlebercongenital pages 8-10). In CORD6, ERG demonstrates reduced cone responses with initially preserved rod responses (gao2023phenotypiccharacterizationof pages 1-2, donato2022theimpactof pages 7-10). ERG testing follows ISCEV standards using gold foil corneal electrodes (bouzia2020gucy2dassociatedlebercongenital pages 5-8).

Optical Coherence Tomography (OCT): Spectral-domain OCT reveals the characteristic structure-function dissociation in LCA1, with preserved ellipsoid zone (EZ) and external limiting membrane (ELM) despite severe visual impairment (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 10-14, hahn2022thenaturalhistory pages 1-2). In CORD6, OCT shows progressive retinal thinning, loss of outer retinal bands, and macular atrophy (gao2023phenotypiccharacterizationof pages 1-2, gao2023phenotypiccharacterizationof pages 7-8). EZ and ELM integrity on OCT correlate significantly with visual acuity outcomes (hahn2022thenaturalhistory pages 1-2).

Fundus Autofluorescence (FAF): Variable patterns from normal appearance to central and mid-peripheral hypoautofluorescence with variable hyperautofluorescent foci (bouzia2020gucy2dassociatedlebercongenital pages 14-16).

Fundus Photography: In LCA1, fundi may appear near-normal early in life. In CORD6, progressive RPE granularity and macular atrophy are characteristic (gao2023phenotypiccharacterizationof pages 1-2, gao2023phenotypiccharacterizationof pages 7-8).

Genetic Testing

Molecular confirmation is essential and typically employs: - Targeted next-generation sequencing (NGS) panels of inherited retinal dystrophy genes (bouzia2020gucy2dassociatedlebercongenital pages 5-8) - Whole exome sequencing (WES) for cases not resolved by panels (bouzia2020gucy2dassociatedlebercongenital pages 5-8) - Whole genome sequencing (WGS) for comprehensive analysis (bouzia2020gucy2dassociatedlebercongenital pages 5-8) - Sanger sequencing for validation and segregation analysis (bouzia2020gucy2dassociatedlebercongenital pages 5-8) - Variants are classified per ACMG/AMP guidelines and cross-referenced with ClinVar (huang2021leber’scongenitalamaurosis pages 5-6)

Differential Diagnosis

GUCY2D-LCA must be distinguished from other forms of LCA caused by different genes (RPE65, CEP290, CRB1, RDH12, AIPL1, etc.). The relatively preserved retinal structure on OCT despite severe functional impairment is a distinguishing feature of GUCY2D-LCA compared to other LCA subtypes that show extensive early photoreceptor loss (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 10-14).

11. Outcome/Prognosis

LCA1 Prognosis

Visual acuity in GUCY2D-LCA is profoundly reduced from infancy but remains relatively stable over time, with 76% of patients severely visually impaired (hand movements or worse) and only 24% able to record visual acuity on standard charts (bouzia2020gucy2dassociatedlebercongenital pages 5-8). Despite the severe functional deficit, the relatively preserved retinal structure suggests a therapeutic window for gene therapy intervention (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 10-14). Life expectancy is not reduced in non-syndromic cases.

CORD6 Prognosis

GUCY2D-associated CORD shows clearly progressive visual decline with a mean annual worsening of approximately 0.022 logMAR. The disease results in a 32% probability of blindness or severe visual impairment by age 40, culminating in severe visual impairment during mid-to-late adulthood (hahn2022thenaturalhistory pages 1-2).

Prognostic Factors

Genotype-phenotype correlations serve as prognostic indicators: patients with missense variants in exon 2 (extracellular domain) demonstrate milder LCA phenotypes with better-preserved visual acuity over time (bouzia2020gucy2dassociatedlebercongenital pages 10-14). Residual cone-photoreceptor vision correlates with the biochemical properties of specific mutations (bouzia2020gucy2dassociatedlebercongenital pages 14-16).

12. Treatment

The following table summarizes current and experimental therapies:

Table: This table summarizes the current therapeutic landscape for GUCY2D-related retinopathy, spanning active clinical gene therapy, preclinical programs, experimental genome editing concepts, and standard supportive care. It is useful for quickly comparing trial status, delivery route, reported outcomes, and knowledge-base-ready intervention terms.

Gene Therapy (ATSN-101)

The most advanced therapeutic intervention is ATSN-101, an AAV5-based gene augmentation therapy using the GRK1 promoter to deliver the human GUCY2D transgene via unilateral subretinal injection (boye2023preclinicalstudiesin pages 1-2, gong2024infantilenystagmussyndrome—associated pages 11-12). The Phase I/II clinical trial (NCT03920007), sponsored by Atsena Therapeutics Inc., enrolled 15 participants with biallelic GUCY2D mutations and is currently active but not recruiting (NCT03920007 chunk 1). Preliminary results report a mean improvement of 20.3 dB on full-field stimulus testing, with 3 of 6 treated patients reaching the maximum score on the Multi-Luminance Mobility Test (MLMT), and no serious adverse effects reported (saripalli2026genetherapyand pages 2-4). A separate publication in The Lancet (2024) described this as a multicentre, open-label, unilateral dose escalation study demonstrating safety and efficacy signals (wong2025monogenicretinaldiseases pages 21-21). The study completion date is estimated for May 2027, with estimated first results submission by September 2025 (NCT03920007 chunk 1).

GUCY2D-LCA is considered particularly favorable for gene therapy because of the characteristic preservation of central photoreceptor structure despite severe functional impairment, providing viable cellular targets for gene replacement (varela2022lebercongenitalamaurosisearlyonset pages 3-3).

Preclinical Gene Therapy

Preclinical studies in GCDKO (guanylate cyclase 1/2 double knockout) mice demonstrated sustained and statistically significant improvements in both photopic (cone) and scotopic (rod) retinal function at 3 months post-injection with high-dose AAV5-hGRK1-GUCY2D (boye2023preclinicalstudiesin pages 1-2). Dose-ranging studies in cynomolgus monkeys established minimum effective doses, and GLP biodistribution and toxicology studies in rats and non-human primates supported clinical translation (boye2023preclinicalstudiesin pages 1-2). An avian model of childhood blindness also demonstrated vision restoration after lentiviral expression of RetGC-1 (bouzia2020gucy2dassociatedlebercongenital pages 14-16).

CRISPR/Genome Editing

Successful knockout of the GUCY2D coding sequence in mouse and macaque photoreceptors has been demonstrated as proof-of-platform for retinal genome editing, though no disease-specific CRISPR clinical trial for GUCY2D retinopathy is currently active (gong2024infantilenystagmussyndrome—associated pages 11-12).

Supportive Care

Current standard management includes low-vision rehabilitation, orientation and mobility training, educational support, and genetic counseling (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 5-8). MAXO terms: MAXO:0000015 (genetic counseling); MAXO:0001001 (gene therapy).

13. Prevention

Primary Prevention

As a purely genetic disorder, primary prevention centers on: - Genetic counseling (MAXO:0000015): Risk assessment, carrier identification, and family planning guidance for autosomal recessive (LCA1) and autosomal dominant (CORD6) inheritance patterns (varela2022lebercongenitalamaurosisearlyonset pages 3-3, bouzia2020gucy2dassociatedlebercongenital pages 1-5) - Carrier screening: Relevant for consanguineous couples in populations with high carrier frequency - Preimplantation genetic diagnosis (PGD) and prenatal testing: Available for families with known pathogenic variants

Secondary Prevention

• Early genetic diagnosis through NGS panels enables timely identification and enrollment in clinical trials (huang2021leber’scongenitalamaurosis pages 5-6)
• Cascade genetic testing of family members to identify at-risk individuals (hahn2022thenaturalhistory pages 1-2)

Tertiary Prevention

• Gene therapy (when available) aims to restore RetGC-1 function before irreversible photoreceptor loss (boye2023preclinicalstudiesin pages 1-2, varela2022lebercongenitalamaurosisearlyonset pages 3-3)
• Low-vision aids and rehabilitation to maximize functional vision (bouzia2020gucy2dassociatedlebercongenital pages 5-8)

14. Other Species / Natural Disease

Comparative Biology

The mouse orthologue of GUCY2D is Gucy2e, with Gucy2f encoding the paralogous RetGC-2. The GCDKO (GC1/GC2 double knockout) mouse, carrying disruptions in both Gucy2e and Gucy2f, recapitulates the human LCA1 phenotype with loss of rod and cone photoreceptor function and has been the primary preclinical model for gene therapy development (boye2023preclinicalstudiesin pages 1-2). An avian (chicken) model of RetGC-1 deficiency has also been used to demonstrate vision restoration through gene therapy (bouzia2020gucy2dassociatedlebercongenital pages 14-16).

A recent publication (2025) describes a naturally occurring GUCY2D-associated retinopathy in German Spitz dogs, representing a veterinary comparative model (unobtained reference: Guareschi et al., Vet Sci 2025).

15. Model Organisms

Mouse Models

• GCDKO (GC1/GC2 double knockout): Carries disruptions in Gucy2e and Gucy2f; shows complete loss of rod and cone function with progressive photoreceptor degeneration. Gene therapy with AAV5-hGRK1-GUCY2D restores both scotopic and photopic retinal function (boye2023preclinicalstudiesin pages 1-2).
• GC1 single knockout mice: Used for studying cone arrestin translocation and testing AAV-GC1 gene therapy approaches (bouzia2020gucy2dassociatedlebercongenital pages 14-16).
• Gucy2d-Cre knock-in mice: Created via CRISPR/Cas9 for studying cellular expression patterns; show Gucy2d expression in spinal dorsal horn neurons in addition to retinal expression, though knockout mice do not exhibit altered behavioral responses under naïve conditions (OpenTargets Search: -GUCY2D).

Avian Models

Chicken models of RetGC-1 deficiency have demonstrated successful lentiviral gene replacement therapy restoring vision, providing proof-of-concept for mammalian translation (bouzia2020gucy2dassociatedlebercongenital pages 14-16).

Non-Human Primates

Cynomolgus monkeys (Macaca fascicularis) have been used for dose-ranging studies, biodistribution assessment, and toxicology evaluation of AAV5-hGRK1-GUCY2D in support of the ATSN-101 clinical trial (boye2023preclinicalstudiesin pages 1-2).

Model Limitations

Mouse models have anatomical differences from the human retina (smaller eye, rod-dominant retina with no true macula), which limits direct translation of dosing parameters. Non-human primate models provide better anatomical correspondence but cannot model the disease phenotype since they have wild-type GUCY2D. The GCDKO mouse involves knockout of both RetGC isoforms rather than Gucy2e alone, creating a more severe phenotype than most human GUCY2D-LCA patients (boye2023preclinicalstudiesin pages 1-2).

Summary

GUCY2D-related retinopathy represents a well-characterized spectrum of inherited retinal diseases ranging from congenital blindness (LCA1) to progressive cone-rod degeneration (CORD6), unified by dysfunction of the retinal guanylate cyclase-1 enzyme central to photoreceptor cGMP signaling. The disease is notable for the structure-function dissociation in the recessive form, where photoreceptors remain anatomically intact despite functional silence, creating a favorable therapeutic window for gene replacement therapy. The Phase I/II ATSN-101 clinical trial (NCT03920007) represents the most advanced therapeutic intervention, with preliminary results demonstrating safety and efficacy in restoring visual function in patients with decades-long congenital blindness. Continued development of gene therapy and potential genome editing approaches holds promise for transforming outcomes in this otherwise untreatable condition.

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