Spinal Muscular Atrophy (SMA) is a neuromuscular disease that results from production of a non-working form of the SMN (Survival of Motor Neuron) protein. There are three types of SMA, numbered I, II, and III. Type II and Type III SMA, the milder forms of the disease, are sometimes referred to as intermediate or progressive SMA. Severity between the two types can range from complete inability to walk to displaying no noticeable symptoms into adulthood. Hydroxyurea is a drug that has been shown to increase the amount of working SMN protein produced by certain cells in culture. The purpose of this trial is to test the safety and efficacy of hydroxyurea in treating Type II and severe Type III SMA patients.

Participation in our research will require regular visits to Stanford to be seen by our Primary Investigator over a period of at least 7 months (one month of observation before beginning six months of treatment with either hydroxyurea or placebo). At some of these visits, your son or daughter will have tests done to measure their muscle strength and breathing ability. Each month, our physical therapist will conduct some testing to measure your child’s movement. We will also perform frequent blood work to monitor your child’s safety and monitor the amount of SMN protein and a certain kind of SMN RNA, the molecule that makes SMN protein.

Ages Eligible for Study:  16 Months   -   10 Years,  Genders Eligible for Study:  Both

Criteria

Inclusion Criteria:

• Laboratory confirmation of homozygous deletion of the SMN1 gene (genetic testing)
• Patient is between the ages of 16 months and 10 years
• The patient is EITHER at least 16 months old and has never walked independently OR the patient walked when less than 2 years of age, but began using mechanical assistance (wheelchair, walker, braces, etc.) for mobility before the age of 6 years

Exclusion Criteria:

• Known hematological disorders (anemia, thrombocytopenia, etc.), severe systemic disorders or birth defects (heart, lung, kidneys, etc.), or neurological diseases other than SMA
• Severe birth asphyxia
• Participation in other clinical trials testing drugs against SMA
• Currently receiving full-time respiratory support

The test we will use to measure your son or daughter’s lung function cannot be performed if they cannot breathe unassisted for at least an hour. If they use respiratory support only at certain times of day (such as Bi-PAP at nap time), then they are still eligible.