Study to Evaluate the Safety and Efficacy of Aceneuramic Acid Extended-Release (Ace-ER) Tablets in Patients With Glucosamine (UDP-N-acetyl)-2-epimerase Myopathy (GNEM) or Hereditary Inclusion Body Myopathy (HIBM)

The objective of this study is to evaluate the long-term safety and efficacy of Ace-ER treatment in subjects with GNEM.

This Phase 3b extension study will assess the long-term safety of Ace-ER in patients who participated in and completed study UX001-CL301 (NCT02377921), study UX001-CL202 (NCT01830972), and study UX001-CL203 (NCT02731690).

Eligibility Criteria:
Inclusion Criteria:

* Have completed UX001-CL202, UX001-CL301 or UX001-CL203 study
* Willing and able to provide written, signed informed consent after the nature of the study has been explained, and before any research-related procedures are conducted
* Willing to comply with all study procedures
* Female participants of child-bearing potential or male participants with female partners of child-bearing potential who have not undergone a bilateral salpingo-oophorectomy and are sexually active must consent to use a highly effective method of contraception as determined by the site investigator (i.e., oral hormonal contraceptives, patch hormonal contraceptives, vaginal ring, intrauterine device, physical double-barrier methods, surgical hysterectomy, vasectomy, tubal ligation or true abstinence \[when this is in line with the preferred and usual lifestyle of the subject\], which means not having sex because the subject chooses not to), from the period following the signing of the informed consent through 30 days after last dose of study drug
* Females of childbearing potential must have a negative pregnancy test at Screening and be willing to have additional pregnancy tests during the study. Females considered not of childbearing potential include those who have been in menopause for at least two years, have had tubal ligation at least one year prior to Screening, or who have had a total hysterectomy or bilateral salpingo oophorectomy

Exclusion Criteria:

Individuals who meet any of the following exclusion criteria will not be eligible to participate in the study:

* Ingestion of N-acetyl-D-mannosamine (ManNAc) or related metabolites; intravenous immunoglobulin (IVIG); or anything that can be metabolized to produce SA in the body within 60 days prior to the Screening Visit
* Has had any hypersensitivity to sialic acid (SA) or its excipients that, in the judgment of the investigator, places the subject at increased risk for adverse effects
* Pregnant or breastfeeding at Screening or planning to become pregnant (self or partner) at any time during the study
* Use of any investigational product or investigational medical device within 30 days prior to Screening, or anticipated requirement for any investigational agent prior to completion of all scheduled study assessments
* Has a condition of such severity and acuity, in the opinion of the investigator, that it warrants immediate surgical intervention or other treatment or may not allow safe participation in the study
* Has a concurrent disease, active suicidal ideation, or other condition that, in the view of the investigator, places the subject at high risk of poor treatment compliance or of not completing the study, or would interfere with study participation or would affect safety