The purpose of this study is to evaluate the safety and clinical pharmacology of a single dose pharmacokinetics and pharmacodynamics of XOMA 358 in subjects with hypoglycemia associated with congenital hyperinsulinism.

Inclusion Criteria:

• Clinical diagnosis of congenital hyperinsulinism
• Duration of glucose levels less than 70mg/dL, by CGM, for an average of at least 120 minutes a day across baseline Days -3, -2, and -1 with no single duration less than 60 minutes on any of the baseline Days -3, -2, or -1, unless the subject received rescue treatment.
• Can safely washout of background medications used to treat hyperinsulinism.

Exclusion Criteria:

• Use of any agent, such as diazoxide, octreotide, chronic systemic glucocorticoids, or β agonists that may affect glucose metabolism
• Body Mass Index ≥ 35 kg/m2
• Pregnant females, females planning to become pregnant during the course of the study, females who have delivered 3 months before screening, or breastfeeding
• Male subjects who are planning a pregnancy with a female partner during the course of the study or within 4 months after administration of study drug.