Glycogen-storage and carbohydrate metabolism disorders — formative SAQs

SAQ 1 (10 marks)

A six-month-old boy presents with a distended abdomen noticed by his parents, recurrent early-morning lethargy and one generalised seizure. He feeds every three to four hours and becomes clammy and irritable if a feed is delayed. Examination reveals marked hepatomegaly (liver edge 8 cm below the costal margin), a doll-like facies and growth faltering. A blood sample drawn during a symptomatic, fasted episode shows glucose 1.8 mmol/L, lactate 7.2 mmol/L, urate 0.52 mmol/L, triglycerides 9.1 mmol/L, and a pH 7.28 with a high anion gap; ketones are low. ^{[1] [2]}

a) Give the most likely diagnosis and explain how the biochemical tetrad (hypoglycaemia, lactic acidosis, hyperuricaemia, hypertriglyceridaemia with low ketones) arises from the underlying enzyme block. (3 marks) ^[1]

b) Outline the definitive confirmatory testing, distinguishing molecular genetic testing from a liver enzyme biopsy and stating which you would favour first and why. (2 marks) ^[1]

c) Detail the long-term dietary and metabolic management, including the role of uncooked cornstarch, continuous overnight glucose, fructose and galactose restriction, and the written sick-day plan. (3 marks) ^{[1] [2]}

d) Describe the long-term complications that must be actively surveyed for in this child. (2 marks) ^[1]