Sign in →

Test ID: PMMIL Phosphomannomutase and Phosphomannose Isomerase, Leukocytes

Reporting Name

PMM-PMI, Leukocytes

Useful For

Diagnosing 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


Follow-up testing for patients with an abnormal transferrin isoform profile


This test is not useful for carrier testing.

Specimen Type

Whole Blood ACD

Ordering Guidance

The initial screening test for congenital disorders of glycosylation is transferrin isoform analysis (CDG / Carbohydrate Deficient Transferrin for Congenital Disorders of Glycosylation, Serum). The results of the transferrin isoform analysis should be correlated with the clinical presentation to determine the most appropriate testing strategy, which may include this test.

Shipping Instructions

For optimal isolation of leukocytes, it is recommended the specimen arrive refrigerated within 48 hours of collection to be stabilized. Collect specimen Monday through Thursday only and not the day before a holiday. Specimen should be collected and packaged as close to shipping time as possible.

Specimen Required


Preferred: Yellow top (ACD solution B)

Acceptable: Yellow top (ACD solution A)

Specimen Volume: 6 mL

Collection Instructions: Send in original tube. Do not transfer blood to other containers.

Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood ACD Refrigerated 72 hours YELLOW TOP/ACD

Reference Values


Normal >350 nmol/h/mg protein



Normal >1,300 nmol/h/mg protein

Day(s) Performed


Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
PMMIL PMM-PMI, Leukocytes In Process


Result ID Test Result Name Result LOINC Value
50836 Specimen 31208-2
50837 Specimen ID 57723-9
50838 Source 31208-2
50839 Order Date 82785-7
50840 Reason For Referral 42349-1
50841 Method 49549-9
50842 Phosphomannomutase, Leuko 78970-1
50843 Phosphomannose Isomerase, Leuko 78963-6
50844 Interpretation 59462-2
50845 Amendment 48767-8
50846 Reviewed By 18771-6
50847 Release Date 82772-5

Clinical Information

Congenital disorders of glycosylation (CDG), formerly known as carbohydrate-deficient glycoprotein syndrome, are a group of inherited metabolic diseases that affect one of the steps of the pathway involved in glycosylation. CDG typically present as multisystemic disorders and may include 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 (PMM2-CDG or CDG-Ia) is an autosomal recessive glycosylation disorder resulting from reduced or absent activity of the enzyme phosphomannomutase-2, encoded by the PMM2 gene. It is the most common CDG worldwide. Patients with CDG-Ia have moderate to severe neurological disease, more or less typical dysmorphology, and variable involvement of other organ systems. Severely affected individuals with CDG-Ia usually present in the neonatal period with failure to thrive, developmental delay, abnormal subcutaneous fat distribution, elevated liver transaminases, and abnormal MRI findings. Later presenting individuals can have clinical features that include ataxia, significantly delayed motor and language development, seizures, stroke-like episodes, retinitis pigmentosa, joint contractures and skeletal deformities. An adult form has also been described. Currently, there is no cure and treatment remains primarily supportive and symptomatic.


Phosphomannose isomerase deficiency (MPI-CDG or CDG-Ib) is an autosomal recessive glycosylation disorder resulting from reduced or absent activity of phosphomannose isomerase, an enzyme encoded by the MPI gene. This CDG subtype is unique in that there is little to no involvement of the central nervous system. It is mainly hepatic-intestinal without dysmorphology, and 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.


Normal results are not consistent with either phosphomannomutase-2 deficiency (PMM2-CDG or CDG-Ia) or phosphomannose isomerase deficiency (MPI-CDG or CDG-Ib).


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.

Clinical Reference

1. Grunewald S, Schollen E, Van Schaftingen E, Jaeken J, Matthijs G: High residual activity of PMM2 in patients' fibroblasts: possible pitfall in the diagnosis of CDG-Ia (phosphomannomutase deficiency). Am J Hum Genet. 2001 Feb;68(2):347-354

2. Pirard M, Matthijs G, Heykants L, Schollen E, Grunewald S, Jaeken J, van Schaftingen E: Effect of mutations found in carbohydrate-deficient glycoprotein syndrome type IA on the activity of phosphomannomutase 2. FEBS Lett. 1999 Jun 11;452(3):319-322

3. Sparks SE, Krasnewich DM: Congenital disorders of N-linked glycosylation pathway overview. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2005. Updated January 30, 2014. Accessed July 30, 2020. Available at

4. Sparks SE, Krasnewich DM: PMM2-CDG (CDG-Ia) In: Adam MP. Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2005. Updated October 29, 2015. Accessed July 30, 2020. Available at

5. Scott K, Gadomski T, Kozicz T, Morava E: Congenital disorders of glycosylation: new defects and still counting. J Inherit Metab Dis. 2014 Jul;37(4):609-617.

6. Jaeken J, Matthijs G, Carchon H, Van Schaftingen E: Defects of N-glycan synthesis. In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed July 30, 2020. Available at

Report Available

30 to 45 days

Method Name



1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Biochemical Genetics Patient Information (T602) in Special Instructions

3. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information: