Inclusion criteria :

• Primary population and adult secondary population: age ≥ 18 years
• Juvenile/adolescent secondary population: 2 ≥ age < 18 years with weight ≥ 10 kg
• Participants with a diagnosis of late onset GM2 gangliosidosis (Tay-Sachs disease and Sandhoff disease) caused by genetic β-hexosaminidase deficiency resulting from mutations in the HEXA or HEXB genes (primary population only); a secondary population will enroll patients with diagnosis of juvenile/adolescent GM2 gangliosidosis, GM1 gangliosidosis, saposin C deficiency, sialidosis type 1 or juvenile adult galactosialidosis
• For primary population, the participant has the ability to perform the 9-HPT at the screening visit in < = 240 seconds for the 2 consecutive trials of the dominant hand and the 2 consecutive trials of the nondominant hand.
• Participants with a history of seizures well controlled by medication other than strong or moderate inducer or inhibitor of CYP3A4
• Participant is cooperative, able to ingest oral medication, willing to travel to a study site (if applicable), and able to comply with all aspects of the study, including all assessments, according to the Investigator's judgement
• Signed written informed assent/consent
• Contraception for sexually active male participants or female patient; not pregnant or breastfeeding; no sperm donating for male participant

Exclusion criteria:

• Participant has clinical features of Tay-Sachs or Sandhoff disease, not caused by β-hexosaminidase deficiency resulting from mutations in the HEXA or HEXB genes and/or is without clinical features
• For primary population and participants with juvenile/adolescent late onset GM2 gangliosidosis and GM1 gangliosidosis, the participant cannot understand and perform all age-appropriate study assessments with the exception of 25FWT and PROs.
• Relevant medical disorders that would compromise his/her safety
• Documented diagnosis of hepatitis B, C, human immunodeficiency virus 1 or 2
• World Health Organization (WHO) grade >= 2 cortical cataract or a grade >= 2 posterior subcapsular cataract; patients with nuclear cataracts will be accepted
• Participant who requires invasive ventilatory support
• Current treatment by anticoagulants, cataractogenic medications or any medications that may worsen the vision of patient with cataract
• Previous treatment with substrate reduction therapy (SRT) within 3 months prior to study enrollment, strong or moderate inducers or inhibitors of CYP3A4 within 14 days or 5 half-lives prior to enrollment. This also includes the consumption of grapefruit, grapefruit juice or grapefruit products within 72hrs prior to starting investigational medicinal product (IMP) administration.
• Current participation in another study
• Use of investigational medicinal product (IMP) within 3 months or 5 half-lives, whichever is longer, before study enrollment (for N-acetyl-leucine, within 5 half-lives before study enrollment).
• Liver enzymes (alanine aminotransferase [ALT]/aspartate aminotransferase [AST]) or total bilirubin > 2 x the upper limite of normal (ULN) at the time of screening unless the participant has the diagnosis of Gilbert syndrome and maintains a level of bilirubin < 5 mg/dl and direct bilirubin < 20% (1 mg/dl) of total bilirubin level
• Renal insufficiency is defined by estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73m2 at the screening visit

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.