Safety of Urate Elevation in Amyotrophic Lateral Sclerosis (ALS)

Inclusion Criteria: 1. Age 18-85. 2. Sporadic or familial ALS diagnosed as possible, laboratory-supported probable, probable, or definite as defined by revised El Escorial criteria (Appendix 1). 3. Slow vital capacity (SVC) ≥ 60% of predicted for age, height, and gender at the Screening Visit. 4. Capable of providing informed consent and following trial procedures. 5. Serum urate \< 5.5 mg/dL at screening (i.e. below the population median serum urate levels). 6. Women must not be able to become pregnant (e.g. post menopausal, surgically sterile, or using adequate birth control methods) for the duration of the study and 3 months after study completion. Adequate contraception includes: abstinence, hormonal contraception (oral contraception, implanted contraception, injected contraception or other hormonal (patch or contraceptive ring, for example) contraception), intrauterine device (IUD) in place for ≥ 3 months, barrier method in conjunction with spermicide, or another adequate method. 7. Is able and willing to participate in the Mobile app study procedures. Exclusion Criteria: 1. History of urolithiasis. 2. Urine pH \< 5.5 at screening (as acidic urine is a major determinant of uric acid urolithiasis). 3. History of gout. 4. History of stroke or myocardial infarction. 5. History of symptomatic coronary artery disease (e.g. angina pectoris) or symptomatic peripheral arterial disease within 1 year prior to Screening. 6. Symptomatic congestive heart failure with a documented ejection fraction below 45%. 7. Poorly controlled arterial hypertension (SBP\>160mmHg or DBP\>100mmHg at Screening). 8. Women who are pregnant or lactating. 9. The presence of unstable psychiatric disease, cognitive impairment, or dementia that would impair ability of the subject to provide informed consent, according to Site Investigator judgment, or a history of active substance abuse within the prior year. 10. Anything that, in the opinion of the Site Investigator, would place the subject at increased risk or preclude the subject's full compliance with or completion of the study. 11. Use of the following within 30 days prior to Screening: inosine, allopurinol, probenecid, more than 300mg vitamin C daily (note that a subject may take a standard multivitamin up to one tablet or capsule daily). Use of thiazides is permissible as long as the subject is on a stable dose from 1 week prior to Screening. 12. Known hypersensitivity or intolerability to inosine. 13. Renal insufficiency as defined by eGFR \< 60 mL/min/1.73m2 at the time of screening.