Inclusion Criteria: 

• Provide written informed consent signed by the participant or their legal guardian or parent. The parent and/or legal guardian can read, understand, and sign informed consent. Where appropriate, assent will also be sought for participants aged <18 years.
• Confirmed GM1 gangliosidosis or Tay-Sachs, Sandhoff, or GM2AB variant disease based on:
  • Enzymatic test (not applicable for GM2AB disease): if enzymatic activity is lower than the normal laboratory range, the results must be confirmed by repeating the assay on two different blood samples
  • Genetic test: presence of biallelic pathogenic or likely pathogenic variants according to the American College of Medical Genetics and Genomics classification, or one pathogenic variant and one variant of unknown significance if the disease has been confirmed with at least one enzyme activity test showing values lower than the normal laboratory range. GM2AB diagnosis with unknown significance variants will be acceptable if supported by total plasma or dry blood spot levels of GM2 or lyso-GM2 above the normal laboratory range.
• Male and female participants aged 4 years and older at the time of informed consent.
• Onset of neurological symptoms from 1 to 10 years.
• Disability level at Baseline: Ataxic disturbances with a total SARA score of ≥ 3 and ≤ 30 at Baseline: those with a total SARA score of ≥ 5 can enter the study automatically; inclusion of those with a total SARA score of 3 to 5 should be discussed with and approved by the Medical Monitor.
• Willing and able to complete assessments.
• Able to take study medication.
• Females of childbearing potential (defined as a premenopausal female capable of becoming pregnant) are eligible if:
  • Sexually inactive and willing to stay inactive during the study (sexual abstinence for the 14 days prior to the first study drug dose and confirmation of continued abstinence until 28 days after the last dose)
  • Using one of the following highly-effective contraceptives (i.e., <1% failure rate when used consistently and correctly) for 14 days prior to the first study drug dose and continuing until 28 days after the last dose: intrauterine device; surgical sterilization of the partner (vasectomy for a minimum of 6 months); combined (estrogen or progestogen containing) hormonal contraception associated with inhibition of ovulation (oral, intravaginal, or transdermal); progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable, or implantable); or intrauterine hormone releasing system.
• Females of non-childbearing potential are eligible if they:
  • Have undergone one of the following sterilization operations at least 6 months prior to receiving the first dose of study drug: hysteroscopic sterilization; bilateral salpingectomy; hysterectomy; bilateral oophorectomy
  • Are postmenopausal with at least 1 year of amenorrhea and follicle stimulating hormone (FSH) serum values consistent with postmenopausal status. At Screening, postmenopausal women will have their FSH levels analyzed and central laboratory FSH levels should fall within the postmenopausal range
  • Are pre-menarchal at Screening and agree to stay sexually inactive during the study and until 28 days after the last dose or are using one of the contraceptive methods listed in inclusion criterion 8.
• Non-vasectomized male participants are eligible if they consent to use a spermicideimpregnated condom or abstain from sexual activity until 90 days after the last dose of study medication; their female partner is required to consent to comply with this inclusion criterion.
• A vasectomized male who had the procedure at least 6 months before starting the study is eligible if they consent to use a condom during sexual activity. A man vasectomized less than 6 months before commencement of the study must adhere to the same restrictions as a nonvasectomized male.
• Male participants agree not to donate sperm from the start of study treatment until 90 days after the final dose.
• The participant is willing to give information relating to current drugs/therapies used to manage symptoms of their conditions, including restricted medications.

Exclusion Criteria:

• Any condition at Baseline that, in the opinion of the Principal Investigator, could interfere with study assessments (e.g., severe infection, severe cognitive impairment).
• A history of medical conditions other than GM1 or GM2 gangliosidosis that, in the opinion of the Principal Investigator, would confound scientific rigor or the interpretation of results.
• Body weight of < 10 kg.
• The presence of another neurologic disease.
• The presence of moderate or severe hepatic impairment (alanine aminotransferase [ALT], aspartate aminotransferase [AST] and gamma-glutamyl transferase levels of > 3x the upper limit of normal [ULN]).
• The presence of moderate or severe renal impairment (estimated glomerular filtration rate of < 30 mL/min/1.73 m2 ).
• Total bilirubin of > 2x ULN (isolated bilirubin of > 2x ULN is acceptable if bilirubin is fractionated and direct bilirubin is < 35%).
• Platelet count of < 100x109 /L.
• The dose of any anti-epileptic treatment(s) was not stable (required a change in dose within the previous 3 months) and/or a new anti-epileptic treatment (drug or procedure) was prescribed in the month before Baseline.
• Prior use of an investigational drug within the 3 months before Screening; or prior participation in a clinical study involving gene therapy or stem cell transplantation within 2 years prior to Screening.
• A positive serum pregnancy test (for women of childbearing potential).
• ECG with an average triplicate QTcF interval of > 450 msec for males and > 470 msec for females.
• Received miglustat in the 12 months prior to Baseline, unless:
  • The dose was lower than the maximum dose specified in the miglustat Summary of Product Characteristics for patients with NPC disease
  • The total duration of miglustat dosing was less than 12 months.

Any participants receiving miglustat are required to undergo a 1-month washout period before starting study medication.

• Known allergy to azasugars or any study drug excipient.
• Evidence of suicidal ideation with intent (Type 4 to 5) on the Columbia Suicide Severity Rating Scale (C-SSRS) at Screening; this requirement is only applicable to participants judged by the Principal Investigator to be cognitively capable of understanding the concept of suicide.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 2/28/2025. Questions regarding updates should be directed to the study team contact.