To compare efficacy of Glycosade® with uncooked corn starch (UCCS for the dietary management of hepatic glycogen storage diseases (GSD).

'Glyde' is a prospective, randomised, double-blind, crossover trial to compare the effects of two different starches used in the dietary management of GSD.

The study will recruit 64 patients from six centres in the UK, USA, France and The Netherlands. The planned duration per participant is 2 years.

Participants will be randomised into two equally sized groups:

Arm A- Glycosade intake given first, followed by UCCS 1-6 weeks later Arm B- UCCS intake given first, followed by Glycosade 1-6 weeks later.

The objective of this trial is to establish whether Glycosade® improves outcomes for patients with GSD compared to UCCS therapy by comparing the duration of normal blood sugars, lactate and ketone levels of patients with hepatic GSD (Types I, III, VI and IX) post equivalent intakes of UCCS and Glycosade®.

The first part consists of two (blinded) 12 hour starch load tests administered randomly within a maximum 6 week period. Participants will be randomised to receive either UCCS or Glycosade® for the initial intervention period crossing over to the other product for the second intervention period (part 1).

The second part (unblinded) is a 24 month open follow up whereby participant's will continue on the product considered most suitable by the clinician and patient.

Inclusion Criteria:

• Diagnosed by either genetic mutation analysis or enzymology study (this includes patients with only a single mutation but who also have supportive enzymology consistent with the condition). For those whom mutation analysis is not completed this will be assessed during the study.
• Aged 2 years or older (5 years or older in the USA)
• Established on full intake of uncooked corn starch therapy for at least 6 months

Exclusion Criteria:

• Women who are pregnant or breastfeeding at the start of the study or planning to become pregnant during the study will be excluded.
• children less than 2 years of age