Primary objective:

Characterize the natural history of MoCD type A in terms of survival

Secondary objectives:

1. Evaluate blood and urine for biochemical markers
2. Evaluate head circumference, seizure activity and neurologic outcomes
3. To evaluate brain MRI
4. Compare blood and urine analysis, head circumference, seizure activity and neurologic outcomes to MRI findings

Inclusion Criteria:

1. Both living and deceased patients of any age will be considered for study inclusion.
2. Diagnosis of MoCD or isolated SOX deficiency
3. Documented informed consent

Exclusion Criteria:

1. MoCD Type A patient who was in Study ALX-MCD-501
2. Deceased patients with unknown genotype (as of Amendment 4)

The actual sample size will depend on successful identification of at least 30 MoCD Type A patients