Sorted By Test Name - Mayo Medical Laboratories

PMMIL
89656
Interpretation: Normal results are not consistent with either phosphomannomutase-2 deficiency
(CDG-Ia or PMM2-CDG) or phosphomannose isomerase deficiency (CDG-Ib or MPI-CDG). Markedly
reduced activity of phosphomannomutase is consistent with a diagnosis of CDG-Ia. Markedly reduced
activity of phosphomannose isomerase is consistent with a diagnosis of CDG-Ib. Mild to moderately
reduced enzyme activities will be interpreted in the context of clinical and other laboratory test
information submitted with the specimen.
Reference Values:
PMM
Normal >700 nmol/h/mg Prot
PMI
Normal >1,500 nmol/h/mg Prot
Clinical References: 1. Jaeken J: Congenital Disorders of Glycosylation. Ann N Y Acad Sci
2010;1214:190-198 2. Jaeken J, Matthijs: Congenital Disorders of Glycosylation: A Rapidly Expanding
Disease Family. Annu Rev Genomics Hum Genet 2007;8:261-278 3. Marquardt T, Denecke J: Congenital
disorders of glycosylation: review of their molecular bases, clinical presentations and specific therapies.
Eur J Pediatr 2003 Jun;162(6):359-379
Phosphomannomutase (PMM) and Phosphomannose
Isomerase (PMI), Leukocytes
Clinical Information: Congenital disorders of glycosylation (CDG), formerly known as
carbohydrate-deficient glycoprotein syndrome, are a group of inherited metabolic diseases that affect 1 of
the steps of the pathway involved in glycosylation. CDGs typically present as multisystemic disorders
with developmental delay, hypotonia, abnormal magnetic resonance imaging (MRI) findings,
hypoglycemia, and protein-losing enteropathy. There is considerable variation in the severity of this group
of diseases, which can range from hydrops fetalis to a mild presentation in adults. In some subtypes (Ib, in
particular) intelligence is not compromised. Phosphomannomutase-2 deficiency (CDG-Ia or
PMM2-CDG) is an autosomal recessive glycosylation disorder resulting from reduced or absent activity
of the enzyme phosphomannomutase-2, encoded by the PMM2 gene. Over 700 individuals have been
described to date, making it the most common CDG worldwide. All patients with CDG-Ia have a
neurological manifestation of disease with variable involvement of other organ systems. Typically,
individuals with this disorder present in the neonatal period with failure to thrive, developmental delay,
abnormal subcutaneous fat distribution, elevated liver transaminases, and abnormal MRI findings.
Currently, there is no cure and treatment remains primarily supportive and symptomatic.
Phosphomannose isomerase deficiency (CDG-Ib or MPI-CDG) is an autosomal recessive glycosylation
disorder resulting from reduced or absent activity of phosphomannose isomerase, an enzyme encoded by
the MPI gene. This subtype of CDG is unique in that there is little to no involvement of the central
nervous system. The primary clinical manifestations are a result of aberrant gastrointestinal function. In
particular, individuals with CDG-Ib may present with failure to thrive, hypoglycemia, chronic diarrhea,
and protein-losing enteropathy. CDG-Ib is also unique in that it can be effectively treated with mannose
supplementation, though can be fatal if left untreated.
Useful For: Diagnosis of congenital disorders of glycosylation Ia (phosphomannomutase-2 deficiency
[CDG-Ia or PMM2-CDG]) and Ib (phosphomannose isomerase deficiency [CDG-Ib or MPI-CDG]) as
measured in leukocytes A follow-up test for patients with an abnormal transferrin isoform profile as
determined by isoelectric focusing or liquid chromatography-mass spectrometry (eg, CDG/89891
Carbohydrate Deficient Transferrin for Congenital Disorders of Glycosylation, Serum)
Interpretation: Normal results are not consistent with either phosphomannomutase-2 deficiency
(CDG-Ia or PMM2-CDG) or phosphomannose isomerase deficiency (CDG-Ib or MPI-CDG). Markedly
reduced activity of phosphomannomutase is consistent with a diagnosis of CDG-Ia. Markedly reduced
activity of phosphomannose isomerase is consistent with a diagnosis of CDG-Ib. Mild to moderately
reduced enzyme activities will be interpreted in the context of clinical and other laboratory test
information submitted with the specimen.
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