Challenging Diagnosis of Glycogen Storage Disease Ib in Neonatology

Glycogen storage disease type I (GSDI) is caused by a dysfunction in the G6P system : either the catalytic subunit G6P-alpha (type Ia) or the G6P transporter (type Ib). Type b is the less frequent type. Both disorders are characterized by severe fasting hypoglycemia, hepatomegaly and lactic acidosis. In type b, there is additionnaly neutrophil dysfunction. The disease commonly manifests at 3 to 4 months. We report here a neonatal presentation of GSDIb.

The baby was admitted at day 3 of life for jaundice. He was born at 38 weeks of GA to consanguineous Pakistani parents. Soon after admission,his condition deteriorated : shallow breathing, altered mental status requiring management in PICU. Clinical examination was unremarkable. Labs showed severe lactic acidosis, profound hypoketotic hypoglycemia and deranged LFT. The patient continued to have recurrent asymptomatic hypoglycemia attacks despite high carbohydrate rich diet. The liver span was at the upper limit of the normal range in US. The endocrine workup showed high serum 17 OHP with mildly elevated ACTH but the short synacthene test was normal. The baby was started on hydrocortisone. Cortisol level was borderline and insulin levels were normal. Metabolic workup included plasma amino acids: Increased phosphoethanolamine, proline and alpha aminobutyric acid. Urine organic acids: metabolites of lactic acid and pyruvic acid.

At 1 month of age, a persistent neutropenia was noted. Currently, the baby is 6 months old, his glucose is partially controlled with Q2h feeds. He had 2 episodes of skin infection and 1 episode of UTI. The combination of short fasting hypoglycemia, lactic acidosis, hepatomegaly and persistent neutropenia is highly suggestive of GSD Ib, the genetic study of SLC37A4 is pending.

Diagnosing the GSD I may be challenging in neonatal period. The Neutropenia is the clue for the type Ib.