Observational Study of Males With Creatine Transporter Deficiency

This is an observational study designed to determine an appropriate clinical assessment
battery for males with CTD, and to evaluate MRS along with other potential biomarkers. It is
designed to explore developmental domains of interest and to examine the feasibility and
utility of various neuropsychological assessments to measure domains of interest, and to
identify possible endpoints for interventional studies. Study will also explore
genotype-phenotype correlations.

This study will consist of a Screening Period, a Baseline period, and Ongoing Assessment
Periods. During the Screening Period, subjects will be assessed for study eligibility
including verification of existing laboratory evidence of a pathologic mutation at SLC6A8
gene. A comprehensive history and physical and neurological examination, including evaluation
of growth and dysmorphic features, will be completed for all subjects. During the Baseline
Period, the caregiver will be interviewed and study staff will administer
scales/questionnaires at the study site. For purpose of this protocol, a duly authorized
patient representative (e.g. parent, legal guardian) will be referred to as a caregiver.
Biological, physiological and radiographic assessments, including ERP recordings, MRS, skin
biopsy, cerebrospinal fluid, urine and blood will be obtained. During the Ongoing Assessment
Period, growth assessments and limited physical and neurological examinations will be
performed. All scales/questionnaires will be repeated every 6 months (± 2 weeks) for 48
months either at the study site or with instructions for completion at home.

Clinical adverse events will be monitored throughout the study.

Inclusion Criteria:

1. Subject is male and between 6 months and 65 years of age, inclusive.

2. Subject has genomic confirmation of a pathologic mutation in the SLC6A8 gene.

3. Subject is able to complete study-related procedures.

4. Subjects' parents/guardians/caregivers must provide written consent (informed consent)
to study-related procedures, and if appropriate, the subject will provide an assent.

Exclusion Criteria:

1. Subject has had status epilepticus within 3 months of screening.

2. Subject is unable to comply with the study procedures or with a clinical disease or
laboratory abnormality that in the opinion of the investigator would potentially
increase the risk of participation.