This is an open label study in approximately 6 subjects in 2 centers to assess the safety, PK, and efficacy of the maximum tolerable dose (MTD) of oral miglustat (100 mg once daily [QD] to 200 mg 3 times daily [TID]) in subjects ≥ 17 years of age with CLN3 disease over a period of 104 weeks.

Inclusion Criteria:

Individuals

1. Have provided informed consents (TCH and NIH) by subject or parent/legal guardian/legally authorized representative (as appropriate).

2. Are males or females ≥ 17 years of age at the time of screening

3. Have genetically confirmed diagnosis of syndromic CLN3 disease with

   EITHER:

   A. Two pathogenic mutations in the CLN3 gene, OR B. One confirmed pathogenic AND one variant of unknown significance, OR 2 variants of unknown significance, PLUS (+) secondary confirmation with evidence of characteristic inclusions on electron microscopy AND characteristic clinical course. There is no restriction on the specific CLN3 mutations for eligibility to enroll in the study. The mutations will be recorded in the electronic case report form (eCRF) for potential use in determining if CLN3 genotype is associated with tolerability and/or effectiveness of Beyond Batten Disease Foundation-1 (BBDF-1) (miglustat) therapy.

4. Male and female participants must use a highly effective method of contraception and must continue for the duration of the trial (and for 30 days after the end of treatment).

5. Are able to complete study assessments (subject or caregiver) and return to the clinic as scheduled

Exclusion criteria

Individuals

1. Have a medical condition that in the opinion of the PI would interfere with the safety assessments or increase the subject's risk of adverse events (AEs)
2. Use of any therapy (approved, off-label, or unapproved) intended to modify the course of any neuronal ceroid lipofuscinosis disease, including but not limited to flupirtine or flupirtine derivatives, cerliponase alfa (Brineura)
3. Have, in the opinion of the PI, a clinically significant abnormality in their clinical laboratory values (hematology, chemistry, or urinalysis) at screening that would preclude their participation in the study