• CDG Ib
• carbohydrate deficient glycoprotein syndrome
• phosphomannose isomerase
• inborn errors

Congenital disorders of glycosylation (CDG) are newly described inborn errors of metabolism involving glycan moiety synthesis. CDG Ib is caused by a deficiency of cellular phosphomannose isomerase (EC 5.4.2.28)^1–4 resulting from the presence of mutations in the corresponding gene, MPI,^5,6 on chromosome 15 (mutation database: http://www.med.kuleuven.ac.be/cdg/). CDG Ib differs clinically from the other CDGs. It has no neurological symptoms, presenting mainly with hepatic and gastrointestinal symptoms^2,3,7,8 and is thought to be underdiagnosed. Fewer than 20 CDG Ib patients have been reported. Importantly, CDG Ib is treatable by oral mannose supplementation, in contrast with other CDGs.^3,9

The syndrome of intractable diarrhoea of infancy was first defined in 1968 by Avery et al.¹⁰ In 1986, a syndrome of intractable diarrhoea associated with severe protein losing enteropathy, hypoglycaemia, and congenital hepatic fibrosis, was described in four infants from the Saguenay-Lac St-Jean (SLSJ) region of north eastern Quebec, Canada. All died before 21 months of age.¹¹

In retrospect, their symptoms resembled those of CDG Ib. In this article we describe the testing of parents of these children and report on a new French family with CDG Ib. The French-Canadian parents were all heterozygous for the same deleterious MPI mutation as found in the new French patient, proving that the SLSJ patients in fact suffered from CDG 1b.