RPE65 Gene Testing From TDL (UK) at Chughtai Lab

RPE65 Gene Testing From TDL (UK) at Chughtai Lab

The RPE65 gene testing from TDL (UK) at Chughtai Lab represents a pinnacle of advanced molecular diagnostics, offering patients in Pakistan access to world-class genetic analysis for inherited retinal dystrophies. The RPE65 gene, located on chromosome 1p31, encodes the retinal pigment epithelium-specific 65 kDa protein, also known as retinoid isomerohydrolase. This vital enzyme is primarily expressed in the retinal pigment epithelium (RPE), a specialized monolayer of cells situated beneath the photoreceptor cells of the retina. The RPE65 protein plays an indispensable role in the visual cycle, a complex biochemical pathway that regenerates visual pigments after they have been exposed to light. Specifically, RPE65 catalyzes the conversion of all-trans-retinyl esters to 11-cis-retinol, which is the precursor to 11-cis-retinal. This chromophore binds to opsin proteins to form rhodopsin in rod cells and cone opsins in cone cells, enabling phototransduction—the process by which light is converted into electrical signals that the brain interprets as vision.

When mutations occur in the RPE65 gene, the production of functional retinoid isomerohydrolase is severely compromised or entirely halted. This disruption leads to a critical shortage of 11-cis-retinal, preventing the regeneration of visual pigments and causing a toxic accumulation of retinyl esters within the retinal pigment epithelium. Over time, this biochemical failure results in the progressive degeneration of photoreceptor cells, leading to severe, early-onset visual impairment and, in many cases, complete blindness. Mutations in the RPE65 gene are inherited in an autosomal recessive pattern, meaning an individual must inherit two mutated copies of the gene (one from each parent) to develop the clinical disease. The most common clinical phenotypes associated with biallelic RPE65 mutations are Leber Congenital Amaurosis type 2 (LCA2) and early-onset Retinitis Pigmentosa type 20 (RP20). Identifying these mutations through genetic testing is of paramount clinical importance, particularly with the advent of voretigene neparvovec-rzyl (Luxturna), an FDA-approved gene therapy designed specifically to deliver a functional copy of the RPE65 gene to retinal cells, halting disease progression and restoring functional vision in eligible patients.

To provide this highly specialized test, Chughtai Lab, Pakistan’s leading diagnostic network, collaborates with The Doctors Laboratory (TDL) in the United Kingdom. TDL is a premier provider of laboratory medicine, renowned for its state-of-the-art molecular genetics department. Through this international partnership, Chughtai Lab facilitates the seamless collection, processing, and international transport of patient specimens under strict cold chain conditions. The genetic analysis is performed at TDL UK using advanced Next-Generation Sequencing (NGS) technology, which sequences the entire coding region and adjacent intron-exon boundaries of the RPE65 gene to identify pathogenic variants, insertions, deletions, or splice-site mutations with exceptional clinical sensitivity and specificity.

Clinical Procedure: What to Expect

Patient Preparation

Proper patient preparation is essential to ensure the integrity of the genetic sample and the accuracy of the clinical correlation. Patients undergoing RPE65 gene testing from TDL (UK) at Chughtai Lab should observe the following guidelines:

• No Fasting Required: There is no requirement for fasting prior to the blood draw. Patients may eat and drink normally before the procedure.
• Informed Consent: Genetic testing requires formal, written informed consent. The patient, or a parent/legal guardian in the case of minors, must read, understand, and sign the genetic consent form provided by Chughtai Lab.
• Clinical Documentation: Patients must provide detailed clinical history, including previous ophthalmic reports, electroretinography (ERG) results, optical coherence tomography (OCT) scans, and visual field assessments. This clinical context is invaluable for the interpreting geneticists at TDL UK.
• Family History: If other family members have been diagnosed with inherited retinal dystrophies or have undergone genetic testing, a copy of their genetic reports or a detailed family pedigree should be submitted along with the sample.
• Medication Review: Patients do not need to discontinue any routine ophthalmic or systemic medications prior to the test, but all current medications should be documented on the clinical requisition form.

During the Procedure

The collection and handling of the specimen for RPE65 gene testing follow a rigorous protocol to ensure international transport compliance and sample viability:

• Sample Collection: A certified phlebotomist at Chughtai Lab will perform a standard venipuncture to collect a whole blood sample. The blood is drawn into a sterile EDTA (ethylenediaminetetraacetic acid) tube, typically identified by a lavender/purple top.
• Patient Experience: The venipuncture is a quick, minimally invasive procedure lasting only a few minutes. Patients may feel a mild pinch or stinging sensation as the needle is inserted, but the discomfort is minimal and temporary.
• Sample Labeling and Barcoding: Immediately after collection, the tube is labeled with the patient’s unique identification details, barcode, and date of collection to prevent any risk of sample misidentification.
• Cold Chain Logistics: The collected blood sample is processed and prepared for international shipping. Chughtai Lab maintains a strict, temperature-controlled cold chain, packaging the specimen in specialized diagnostic transport containers to ensure it remains stable during transit from Pakistan to TDL UK.
• Laboratory Analysis: Upon arrival at TDL UK, genomic DNA is extracted from the blood sample. Next-Generation Sequencing (NGS) is employed to analyze the RPE65 gene. Any detected variants are cross-referenced with international genetic databases and classified according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

When is a RPE65 Gene Testing Performed?

1. Diagnosis of Leber Congenital Amaurosis (LCA)

Leber Congenital Amaurosis is a severe, early-onset inherited retinal dystrophy characterized by profound visual impairment from birth or early infancy. Infants with LCA often present with wandering nystagmus (involuntary, rapid eye movements), sluggish or absent pupillary light reflexes, and a tendency to rub their eyes repeatedly (known as the Franceschetti’s oculo-digital sign). Physicians request RPE65 gene testing to confirm a clinical suspicion of LCA type 2, allowing for a definitive molecular diagnosis that distinguishes it from other genetic causes of childhood blindness.

2. Investigation of Early-Onset Retinitis Pigmentosa

Retinitis Pigmentosa is a group of progressive retinal degenerations that primarily affect rod photoreceptors, followed by the gradual loss of cone photoreceptors. Patients with RPE65-related Retinitis Pigmentosa (RP20) typically experience severe night blindness (nyctalopia) in early childhood, followed by a progressive constriction of their peripheral visual field, resulting in “tunnel vision.” Ophthalmic examination may reveal characteristic bone-spicule pigmentary deposits in the retina, optic disc pallor, and retinal vessel attenuation. Genetic testing is performed to identify the underlying RPE65 mutation, providing a clear genetic etiology for the progressive visual loss.

3. Screening for Luxturna Gene Therapy Eligibility

The development of voretigene neparvovec-rzyl (Luxturna) has revolutionized the management of inherited retinal dystrophies. Luxturna is an adeno-associated virus vector-based gene therapy indicated for the treatment of patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy who possess sufficient viable retinal cells. Because this therapy is gene-specific, physicians must order RPE65 gene testing to confirm the presence of pathogenic mutations in both alleles before a patient can be considered a candidate for this life-altering treatment.

4. Genetic Counseling and Family Planning

As an autosomal recessive disorder, parents of an affected child are typically asymptomatic obligate carriers of a single mutated RPE65 allele. When a pathogenic mutation is identified in a family member, RPE65 gene testing is performed on parents, siblings, or partners to determine carrier status. This information is critical for genetic counseling, enabling families to understand the inheritance pattern, assess the recurrence risk (which is 25% for each subsequent pregnancy between two carrier parents), and make informed family planning decisions.

5. Differential Diagnosis of Unexplained Childhood Blindness

In many cases, children presenting with severe visual impairment or atypical retinal findings may undergo a battery of clinical tests without achieving a definitive diagnosis. RPE65 gene testing serves as a powerful diagnostic tool to resolve ambiguous clinical presentations. By identifying or ruling out mutations in the RPE65 gene, clinicians can narrow down the differential diagnosis, avoid unnecessary diagnostic procedures, and establish a precise prognosis for the patient’s visual trajectory.

What Does a RPE65 Gene Testing Detect?

The RPE65 gene testing from TDL (UK) at Chughtai Lab is designed to detect a wide spectrum of genetic variations within the RPE65 gene. The molecular analysis can identify:

• Pathogenic homozygous mutations (the same mutation on both alleles)
• Compound heterozygous mutations (different mutations on each of the two alleles)
• Heterozygous carrier status (a mutation on only one allele)
• Missense mutations resulting in single amino acid substitutions
• Nonsense mutations introducing premature stop codons
• Frameshift mutations caused by small insertions or deletions (indels)
• Splice-site mutations disrupting normal pre-mRNA splicing
• Large genomic deletions or duplications affecting the RPE65 locus
• Variants of Uncertain Significance (VUS) requiring clinical correlation
• Known pathogenic variants associated with Leber Congenital Amaurosis
• Known pathogenic variants associated with Retinitis Pigmentosa
• Novel, previously undescribed mutations in the coding regions
• Synonymous variants that do not alter the amino acid sequence
• Intronic variants located near exon-intron boundaries
• Promoter region variants affecting gene expression
• Polymorphisms with no clinical significance (benign variants)
• Likely pathogenic variants with high probability of causing disease
• Likely benign variants with low probability of causing disease
• Biallelic mutations confirming eligibility for gene therapy
• Absence of mutations, ruling out RPE65-related retinal dystrophy

Turnaround Time and Report Access at Chughtai Lab

Because the RPE65 gene testing is a highly specialized molecular analysis performed in collaboration with The Doctors Laboratory (TDL) in the United Kingdom, the turnaround time reflects the complexity of international logistics and advanced genetic sequencing. Typically, results are available within 3 to 4 weeks from the date of sample collection at Chughtai Lab. This timeframe includes the secure transport of the specimen to London, DNA extraction, Next-Generation Sequencing, bioinformatic analysis, and clinical interpretation by consultant geneticists at TDL UK.

Once the analysis is complete, the comprehensive genetic report is transmitted securely back to Chughtai Lab. Patients and their referring physicians can access the report conveniently through Chughtai Lab’s online portal or the Chughtai Lab mobile application. A physical copy of the report can also be collected from any Chughtai Lab diagnostic center. The report provides a detailed breakdown of the identified genetic variants, their classification according to ACMG guidelines, and a clinical interpretation of the findings in relation to the patient’s symptoms.

RPE65 Gene Testing Findings Overview

Structure / Parameter Evaluated	Normal Findings	Possible Abnormal Findings
RPE65 Coding Regions (Exons 1-14)	No pathogenic or likely pathogenic variants detected.	Pathogenic homozygous or compound heterozygous mutations identified.
Splice Junctions	Intact consensus splice sequences; normal mRNA splicing.	Splice-site mutations disrupting normal pre-mRNA splicing and protein translation.
Variant Classification	Only benign or likely benign polymorphisms observed.	Presence of Pathogenic, Likely Pathogenic, or Variants of Uncertain Significance (VUS).
Allelic Status	Wild-type (two normal copies of the RPE65 gene).	Biallelic mutations (homozygous or compound heterozygous) or single heterozygous carrier state.
Gene Dosage (CNV)	Normal copy number (two copies present, no deletions or duplications).	Heterozygous or homozygous deletions or duplications of one or more exons.
Isomerase Activity (Inferred)	Normal retinoid isomerohydrolase activity; intact visual cycle.	Deficient or absent isomerase activity, leading to visual pigment depletion.
Therapeutic Actionability	Not eligible for RPE65-specific gene therapy.	Eligible for voretigene neparvovec-rzyl (Luxturna) if viable retinal cells are present.

Note: Diagnostic findings should always be interpreted by a qualified healthcare professional together with the patient’s symptoms, medical history, physical examination, laboratory investigations, previous imaging studies, and other relevant clinical information. Additional investigations or specialist consultation may be recommended depending on the findings.

Why Choose Chughtai Lab for RPE65 Gene Testing?

• International Collaboration: Partnered with The Doctors Laboratory (TDL) UK, ensuring world-class genetic sequencing and interpretation.
• Strict Cold Chain Management: Advanced logistical protocols to maintain sample integrity during international transit.
• Accredited Network: Chughtai Lab operates under stringent quality control standards, with ISO 15189 certified facilities.
• Convenient Sample Collection: Available across an extensive network of collection centers in all major cities of Pakistan.
• Secure Online Reports: Easy and quick access to genetic reports via the Chughtai Lab website and mobile app.
• Patient-Focused Care: Dedicated support staff to assist with genetic consent forms and clinical documentation.
• Professional Reporting: Comprehensive genetic reports classified according to international ACMG guidelines.
• Commitment to Accurate Diagnosis: Helping clinicians and patients in Pakistan access cutting-edge precision medicine.