Trial of the Combined Use of Thiamine and Biotin in Patients With Huntington's Disease

The assessment of the safety and tolerability of the combined oral thiamine and biotin therapy in patients with HD will be performed by:

• Periodic clinical examination and anamnesis directed by a neurologist during face-to-face and non-contact visits.
• The collection of adverse effects during interviews of face-to-face visits to assess tolerability.
• Analytical monitoring with hematological and biochemical control (hepatic and renal function) during the dose escalation period, subsequently being this periodic control every 3 months, from signature of informed consent until the end the follow up.

The evaluation of the biological efficacy of treatment with combined oral thiamine and biotin therapy in increasing thiamine monophosphate (TMP) levels in cerebrospinal fluid (CSF) of patients with HD is to be performed by:

• The determination of thiamine levels: free thiamine, TMP, and thiamine pyrophosphate (TTP) in CSF and blood of patients at the beginning and after the end of the study.
• Comparison of thiamine levels (free, TMP and TTP) between the start and the end of the study in CSF and serum of patients with HD.

The evaluation of the biological efficacy of the treatment with combined oral thiamine and oral biotin therapy in neurodegeneration produced in HD will be performed by:

• Measurement of neurofilament light chain protein (NfL) levels in CSF at the baseline visit and after the end of the treatment.
• The obtained score in the motor and Total Functional Capacity (TFC) section of the Unified Huntington's Disease Rating Scale (UHDRS).
• Measurement of bradykinesia through quantitative motion measurement techniques (Quantitative motor assessment, Q-motor). Q-motor assessment relies on three-dimensional position sensors and pre-calibrated force translators, for standardized movement recording. This measurement will be made to patients in the pre-selection visit, randomization, and quarterly face-to-face visits.
• Score on the quality of life scale (SF-36).
• Variation in the overall clinical impression scale of the patient and the examiner.
• Measurement of the change in the volume of the caudate nucleus, white matter, and cortical thickness, as well as in the change of the Combined cerebral atrophy score. Measurements of cerebral structures will be acquired on magnetic resonance imaging scans (3T) at the baseline visit and after the end of the treatment.

To determine the sample size required to examine secondary and exploratory objectives, we based our estimations on the published thiamine-biotin treatment effects in preclinical HD models, and on the reported differences in CSF thiamine levels between HD patients and healthy subjects (Pico S, et al. 2021). According to the previous results, it is expected that a medium-to-high effect size (0.6 ≤ Cohen's d ≥ 0.8) would be necessary to restore TPP, TMP and Free-thiamine levels in CSF after treatment. Based on the parameter choices, for a desired power of 0.80 and a Type I error rate of 0.05, we estimate that we would need 24 HD patients to detect a standardized mean difference of 0.6. Sample size analysis was conducted using GPower 3.1.9.7 software.

The demographic data collection as well as the information related to all the variables analyzed during the study will be done through an electronic data collection notebook. The notification of adverse effects, severity, and relationship with study medication will be done through an electronic data collection notebook.

All statistical analyses will be conducted using SPSS v.26.0. IBM software and R studio software package. Linear regression will be used when the variables are quantitative (eg, scale measurements, CSF thiamine or NfL levels, among others) controlling for age, sex, CAG repetitions and motor symptom severity (UHDRS and UHDRS-Total Functional Capacity) at baseline as potential confounding variables. Logistic or multinomial regression when the variables are groups (binary or multinomial).

We will examine the association between the severity of disease and CSF thiamine among HD patients by fitting a linear mixed model for each clinical measurement, with age, sex, CAG repetitions and disease severity (UHDRS-TFC) as the covariates.

Magnetic resonance imaging performed during the study will be processed with specific neuroimaging programs for volumetry, diffusion and cortical thickness.

Inclusion criteria

• Patients of legal age with manifest Huntington's disease with motor symptoms (chorea, dystonia or bradykinesia) and/or neuropsychiatric; and genetic confirmation of a number of repetitions of the cytosine-adenine-guanine trinucleotide (CAG triplet) in the HTT gene (coding for HTT) greater than or equal to 39
• Patients should be capable of giving informed consent and attending the planned visit of the study.
• Women of childbearing age should obtain a negative result in the serum or urine pregnancy test at the screening visit. They must also accept the use of appropriate contraceptive methods during the course of the clinical trial and men who have a partner of childbearing age, accept the use of contraceptive methods

Exclusion criteria

• Medical comorbidities considered clinically significant by the clinical judgment of the investigators.
• Pregnancy or lactation
• Patients with HD dependents on the basic routine daily life activities (UHDRS TFC < 7) or a severe cognitive decline.
• Active psychosis at the moment of the screening evaluation.
• Severe renal failure.
• Patients previously treated with thiamine and/or biotin or enrolled in other HD clinical trial with oligonucleotide antisense (IONIS-HTTRX (RG6042).