Simple supplement may slow vision loss in rare eye disease

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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.