Study of Serine Supplementation to Protect Vision in MacTel (SEErine)

Phase 3 Study of Serine Supplementation to Protect Vision in MacTel

The goal of this clinical trial is to look at the efficacy and safety of giving oral serine (an amino acid) on the progression of structural and functional changes of the retina in people with MacTel type 2. The main questions it aims to answer are:

• Does serine slow the progression of MacTel?
• Is long-term serine supplementation safe in people with MacTel? Researchers will compare serine to a placebo (a look-alike substance that contains no drug) to see if serine works to slow the progression of MacTel.

Participants will:

• Take serine or a placebo twice a day for 24 months
• Visit the clinic once every 6 months for eye exam, eye imaging and blood tests
• Keep a diary of their symptoms, missed doses, and changes in medications

Study Overview

• Status: Not yet recruiting
• Conditions: Macular Telangiectasia Type 2 (MacTel)
• Intervention / Treatment: Drug: L-serine; Other: Placebo

Detailed Description

Macular telangiectasia type 2 (MacTel) is a bilateral, slowly progressive retinal neurodegenerative disease characterized by photoreceptor loss, vascular abnormalities, and gradual decline in visual function.

Alterations in serine metabolism and the accumulation of toxic deoxysphingolipids have been implicated in the pathophysiology of MacTel. Oral serine supplementation has been proposed as a potential approach to modify this metabolic pathway and reduce the formation of potentially neurotoxic metabolites.

This study is a randomized, double-masked, placebo-controlled, parallel-group clinical trial designed to evaluate the effect of oral serine supplementation on disease progression in participants with macular telangiectasia type 2.

Participants will undergo a screening evaluation to determine eligibility. Eligible participants will be adults aged 18 years or older with a confirmed diagnosis of MacTel through the Natural History Observation Registry (NHOR) study. Participants must meet all eligibility criteria. Eligibility and assignment of the study eye will be determined by review of the images taken at screening. If both eyes are eligible, both eyes may be included as study eyes. A minimum of 110 participants will complete the study.

At the baseline visit, participants will be randomized in a 1:1 ratio to receive either oral serine or placebo. Randomization will be stratified by diabetes status to ensure balanced distribution of participants with and without type 2 diabetes between treatment groups. Participants, investigators, study staff, and outcome assessors will remain masked to treatment assignment throughout the study.

Participants will receive their assigned study treatment for 24 months. In-person study visits will occur every 6 months, with telephone contacts between visits to assess treatment compliance and adverse events. Retinal structure, visual function, and participant safety will be monitored throughout the 24-month treatment period. A follow-up telephone contact will occur approximately 4 weeks after discontinuation of study treatment.

Data will be collected on both eyes of each participant; however, only eyes designated as study eyes and meeting eligibility criteria will be included in the primary efficacy analysis.

The primary objective of the study is to evaluate the effect of serine supplementation compared with placebo on the progression of photoreceptor loss in MacTel. Secondary objectives include the effect of serine supplementation on further structural retinal changes and visual function as well as the assessment of safety and tolerability of long-term oral serine supplementation in this population.

• Study Type: Interventional
• Enrollment (Estimated): 120
• Phase: Phase 3

Contacts and Locations

Study Locations

• Australia
  • New South Wales
    • Sydney, New South Wales, Australia, 2000
      • Save Sight Institute
      • Principal Investigator: Elisa Cornish, MD
      • Contact: Emily Study Coordinator; Phone Number: 61-2-9382-7309; Email: emily.luu@sydney.edu.au
  • Victoria
    • Melbourne, Victoria, Australia, 3002
      • Cerulea- RVEEH
      • Principal Investigator: Robyn Guymer, MD
      • Contact: Carla Study Coordinator, MD; Phone Number: 61-3-9959-0081; Email: cabbott@cera.org.au
• Germany
  • Bonn, Germany, 53127
    • University of Bonn
    • Principal Investigator: Kristina Pfau, MD
    • Contact: Kristin Raming, MD; Phone Number: 49-228-287-5647; Email: Kristin.Raming@ukbonn.de
  • Freiburg im Breisgau, Germany, 79106
    • University of Freiburg, Department of Ophthalmology
    • Principal Investigator: Felicitas Bucher, MD
    • Contact: Wiebke Study Coordinator; Phone Number: 49-761-270-40231; Email: Wiebke.hoch@uniklinik-freiburg.de
    • Contact: Christine Study Coordinator; Phone Number: 49-761-270-40237; Email: christine.kremer@uniklinik-freiburg.de
  • Münster, Germany, 48145
    • St. Franziskus Hospital
    • Principal Investigator: Clemens Lange, MD
    • Contact: Elke Study Coordinator; Phone Number: 0251-935-2758; Email: elke.attenberger@uveitis-zentrum.de
• Netherlands
  • Nijmegen, Netherlands, 6525GA
    • Radboud University Medical Center
    • Contact: Asha Study Coordinator; Phone Number: 24-36-13212; Email: asha.kalisingh@radboudumc.nl
    • Principal Investigator: Suzanne Yzer, MD
• United Kingdom
  • London, United Kingdom, EC1V 2PD
    • Moorfields Eye Hospital
    • Principal Investigator: Cathy Egan, MD
    • Contact: Rabiah Study Coordinator; Phone Number: 02072533411; Email: rabiah.abbassaud@nhs.net
  • Oxford, United Kingdom, OX3 9DU
    • Oxford Eye Hospital
    • Principal Investigator: Samantha De Silva, MD
    • Contact: Alexina Study Coordinator; Phone Number: 01865 231053; Email: alexina.fantato@ouh.nhs.uk
• United States
  • California
    • La Jolla, California, United States, 92093
      • Hamilton Glaucoma Center- UCSD
      • Contact: Veronica Study Coordinator; Phone Number: 858-822-1896; Email: vrubio@health.ucsd.edu
      • Principal Investigator: Chrisopher Toomey, MD, PhD
  • Michigan
    • Ann Arbor, Michigan, United States, 48105
      • University of Michigan, Kellogg Eye Center
      • Principal Investigator: Grant Comer, MD
      • Contact: Maddie Study Coordinator; Phone Number: 734-936-0138; Email: maboss@med.umich.edu
      • Contact: Courtney Study Coordinator; Phone Number: 734-936-9798; Email: cosoto@med.umich.edu
  • Ohio
    • Cleveland, Ohio, United States, 44122
      • Retina Associates of Cleveland, Inc.
      • Principal Investigator: LAWRENCE SINGERMAN, MD
      • Contact: Diane Study Coordinator; Phone Number: 244 216-831-5704; Email: dew@retina-assoc.com
  • Utah
    • Salt Lake City, Utah, United States, 84132
      • University of Utah Health Care, Moran Eye Center
      • Principal Investigator: Paul Bernstein, MD, PhD
      • Contact: Barbara Study Coordinator; Phone Number: 801-581-6459; Email: barbarahart@hsc.utah.edu
      • Contact: Kimberley Study Coordinator; Phone Number: 858-584-6265; Email: Kimberley.wegner@hsc.utah.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria

• Be able to read, comprehend, and agree to conditions as explained in the informed consent document and provide written informed consent;
• Be at least 18 years of age;
• Enrolled or enrolling in the Natural History Observation and Registry Study (NHOR) and confirmed with MacTel type 2 by the Reading Center in at least one eye*;
• Participant has clear ocular media (both eyes) for sufficient image quality;
• Participant must have steady fixation in the foveal or parafoveal area;

• Female participants of childbearing potential must agree to use a highly effective method of contraception from the time consent is signed until six days after treatment discontinuation (this is due to a lack of safety data on use of L-serine in pregnant and breastfeeding women; and to allow for medication wash out post treatment discontinuation). Highly effective methods of contraception include:

  (i)Combined hormonal contraception associated with inhibition of ovulation, (ii) progesterone only hormonal contraception associated with inhibition of ovulation (iii) Intrauterine devices, (iv) surgical sterilization such as bilateral tubal occlusion or vasectomized partner or (v) true abstinence (refraining from heterosexual intercourse during the entire period associated with the study treatments, and the reliability of sexual abstinence is in line with the usual lifestyle of the subject)

• Willing and able to comply with study protocol and follow-up visits
• Agree to unconditional use of their donated samples, images and/or data;
• Be able to fast for at least 10 hours prior to blood specimen collection;
• Have a minimum area of total EZ loss of 0.16 mm2 in the study eye. The Reading Center will determine the exact size once images are uploaded.
• Participant has a BCVA of better than or equal to 20/100 Snellen equivalent (>/= 50 letters) using Early Treatment Diabetic Retinopathy Study (ETDRS) charts at a starting distance of 4 meters in the study eye.

Exclusion Criteria:

• Unable to undergo the study procedures or unavailable for follow up visits;
• Unwilling to agree to blanket consent for use of the acquired data, including human biological specimens and images;
• Participant is pregnant, breastfeeding or planning a pregnancy during the study time period;
• Participant has taken serine or glycine supplements in the last 3 months;
• Participant is currently taking or has been taking Fibrates such as fenofibrate, clofibrate, ciprofibrate, bezafibrate, gemfibrozil within the last 3 months;
• Participant has known allergy or hypersensitivity to serine or rice;
• Participant is currently taking or has been taking tamoxifen, chloroquine (or hydroxychloroquine) and/or other retinotoxic substances; for a total period of 6 months
• Participant has uncontrolled type 1 or type 2 diabetes (defined as an HbA1c level of 9% or higher at screening (with or without medication);
• Participant has uncontrolled hypo- or hyperthyroidism, defined as TSH-levels of below 0.4mU/L or above 4.0mU/L at screening with or without treatment;
• Participant is undergoing chemotherapy, radiation therapy or other treatments for active cancer;
• Participant has significant kidney disease or an estimated glomerular filtration rate <50 ml/min/1.73m2 at screening;
• Participant has an active and/ or chronic liver disease (including viral hepatitis, autoimmune liver disease, hemochromatosis, homozygous alpha1-antitrypsin deficiency and Wilson disease, primary biliary cirrhosis, primary sclerosing cholangitis) or poor liver function as estimated by transaminases (ALT/AST) or gamma glutamyl transferase (GGT) or alkaline phosphatase or bilirubin above 2xULN (upper limit of normal) at screening;
• Participant is currently enrolled in another clinical treatment trial or participated in one within the last 30 days;
• Participant has previously received a CNTF device ("Encelto"; either eye) or has intentions of receiving a CNTF device in either eye during the duration of this study;
• Participant shows signs of retinal diseases other than MacTel (including central serous chorioretinopathy, severe non-proliferative or proliferative diabetic retinopathy, diabetic macular edema, age-related macular degeneration, preretinal membrane) that, in the judgment of the investigator, may confound the diagnosis, procedures or outcome of the study (either eye);
• Participant has a diagnosis of uncontrolled glaucoma with intraocular pressure of >30 mm Hg (despite current pharmacological or non-pharmacological treatment; either eye);
• Participant has evidence of pathologic myopia in either eye;
• Participant has significant corneal or media opacities in either eye;
• Participant has any of the following lens opacities: cortical opacity > standard 3, posterior subcapsular opacity > standard 2, or a nuclear opacity > standard 3 as measured on the Age-Related Eye Disease Study (AREDS) clinical lens grading system (either eye);
• Participant has undergone lens removal in the previous 3 months or YAG laser within the last 4 weeks, in either eye;
• Participant has a chronic requirement (eg, ≥ 4 weeks at a time) for ocular medications (vitamins, supplements and artificial tears are permitted) and/or has a diagnosed disease that, in the judgment of the examining physician, may be vision threatening or may affect the primary outcome in the study eye;
• Participant has had previous ocular treatments that in the judgment of the investigator may complicate the evaluation of the central retina (including vitreo-retinal surgeries, central laser treatments, including central non-damaging retinal laser therapy (either eye); previous peripheral laser treatments or cryotherapy are NOT exclusionary;
• Participant has ever received any periocular or intravitreal injections (including intravitreal anti-vascular endothelial growth factor (anti-VEGF), periocular or intravitreal corticosteroid injections) in the study eye OR participant has received any periocular or intravitreal injections in the fellow eye within the past 3 months
• Participant has evidence of previously active or currently active intraretinal neovascularization or subretinal neovascularization (SRNV), in either eye; subretinal or sub-RPE fibrovascular proliferation or disciform scars (subretinal fibrosis) in either eye are exclusionary;
• Participant has evidence of intraretinal hyperreflectivity** as evaluated by OCT in the study eye;
• Participant has a full thickness macular hole (FTMH) within the foveal area (ETDRS field 1) with a diameter of >400um at its narrowest point and outer retinal atrophy in the study eye;
• Amblyopia in the study eye; or
• Participant is allergic to fluorescein dye, and the clinical site does not have an OCT-A
• Participant has, in the opinion of the Investigator, any physical or mental condition that would increase the patient's risk of participation in the study or may interfere with the study procedures, evaluations and outcome assessments.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: L-serine; Participant receives oral L-serine	Drug: L-serine; L-serine powder administered twice daily
Placebo Comparator: Placebo; Participant receives placebo	Other: Placebo; Placebo powder administered twice daily

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
EZ loss	Mean rate of change in the total area of EZ loss (IS/OS; macular photoreceptor loss) from Baseline (BL) through Month 24 (M24), as assessed using SD-OCT in the study eye(s).	Baseline through Month 24

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
EZ loss at different time points	Mean rate of change in the area of EZ loss (IS/OS; macular photoreceptor loss) from BL through Month 12 (M12) in the study eye(s) and through M12 and M24 in the fellow eye, as assessed using SD-OCT	Baseline through Month 12 and 24
Changes in Disease Severity	Changes in disease severity (stages, according to Chew et al) in study eye(s), and fellow eye, from BL to M24	Baseline through Month 24
Retinal Sensitivity Loss	Mean change in retinal sensitivity loss as measured by Macular Integrity Assessment (MAIA) from BL to M24 in study eye(s), and fellow eye	Baseline through Month 24
Reading Speed	Mean change in monocular and binocular reading speed assessed using International Reading Speed Texts (IReST) cards from BL through M24 in the study eye(s), and fellow eye	Baseline through Month 24
Contrast Sensitivity	Mean change in monocular contrast sensitivity from BL to M24 in the study eye(s) and fellow eye as assessed by Pelli-Robson contrast sensitivity charts	Baseline through Month 24
Low Luminance Visual Acuity	Mean change in monocular low luminance visual acuity (LLVA) scores from BL to M24 in the study eye(s) and fellow eye as assessed by ETDRS charts	Baseline through Month 24
Low Luminance Deficit	Mean change in low luminance deficit (LLVA - BCVA) from BL to M24 in the study eye(s) and fellow eye	Baseline through Month 24
Best Corrected Visual Acuity	Mean change in monocular best-corrected visual acuity (BCVA) scores from BL to M24 in the study eye(s) and fellow eye as assessed by Early Treatment Diabetic Retinopathy Study (ETDRS) charts	Baseline through Month 24
Corneal Nerve fiber Density	Mean change in corneal nerve fiber and branch density (biomarkers of peripheral nerve health) from BL to M6, M12, M18 and M24 in the study eye(s) and fellow eye	Baseline through Month 6, 12, 18 and 24
HbA1c	Mean change in HbA1c from BL to M12 and M24	Baseline through Months 12 and 24
BMI	Mean change in BMI (weight and height will be combined to report BMI in kg/m^2) from BL to M12 and M24	Baseline through Months 12 and 24
Serum Metabolites	Mean changes in fasted serum metabolite values from BL to M12 and M24	Baseline through Months 12 and 24
MacTel Metabolic Signature	Mean changes in composite serum metabolic score measuring the global "MacTel Metabolic signature" from BL to M12 and M24	Baseline through Months 12 and 24
NEI VFQ-25	Mean change in NEI VFQ-25 scores from BL to M12 and M24	Baseline through Month 12 and 24
VILL-33	Mean change in VILL-33 scores from BL to M12 and M24	Baseline through Months 12 and 24
TEAEs and SAEs	Incidence of treatment-emergent adverse events (TEAEs), serious adverse events (SAEs), and ocular TEAEs and SAEs	Baseline through Month 24
ETDRS Letter Score	Number of study eyes, fellow eyes with >= 15 letter loss (ETDRS letter score), >= 10 letter loss and >= 5 letter loss from BL to M24	Baseline through Month 24
Neovascularization	Total number of study eyes, fellow eyes showing a de novo development of neovascularization from BL to M24	Baseline through Month 24
Outer Retinal Hyper-Reflectivity	Total number of study eyes, fellow eyes showing a de novo development of outer retinal hyper-reflectivity from BL to M24	Baseline through Month 24
Hip to waist ratio	Mean change in hip-to-waist ratio from BL to M12 and M24	Baseline through Months 12 and 24
Lipid Levels	Mean change in Lipid Levels from BL to M12 and M24	Baseline through Months 12 and 24
Corneal Nerve Fiber Length	Mean change in corneal nerve fiber length (biomarker of peripheral nerve health) from BL to M6, M12, M18 and M24 in the study eye(s) and fellow eye	Baseline through Months 6, 12, 18 and 24
Corneal Nerve Fiber Tortuosity	Mean change in corneal nerve fiber tortuosity (biomarker of peripheral nerve health) from BL to M6, M12, M18 and M24 in the study eye(s) and fellow eye	Baseline through Months 6, 12, 18 and 24

Collaborators and Investigators

• Sponsor: The Lowy Medical Research Institute Limited

Study record dates

Study Major Dates

• Study Start (Estimated): September 1, 2026
• Primary Completion (Estimated): November 1, 2029
• Study Completion (Estimated): February 1, 2030

Study Registration Dates

• First Submitted: January 7, 2026
• First Submitted That Met QC Criteria: January 13, 2026
• First Posted (Actual): January 15, 2026

Study Record Updates

• Last Update Posted (Actual): January 15, 2026
• Last Update Submitted That Met QC Criteria: January 13, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: MacTel; Serine
• Additional Relevant MeSH Terms: Amino Acids, Peptides, and Proteins; Amino Acids; Amino Acids, Neutral; Serine
• Other Study ID Numbers: 2026-001

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: Yes