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Order Code PMMIL Phosphomannomutase and Phosphomannose Isomerase, Leukocytes

Reporting Name

PMM-PMI, Leukocytes

Useful For

Diagnosing congenital disorders of glycosylation Ia (phosphomannomutase-2 deficiency: PMM2-CDG) and Ib (phosphomannose isomerase deficiency: MPI-CDG) as measured in leukocytes

 

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

 

This test is not useful for carrier testing.

Performing Laboratory

Mayo Clinic Laboratories in Rochester

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 6 days 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


Container/Tube:

Preferred: Yellow top (ACD solution B)

Acceptable: Yellow top (ACD solution A)

Specimen Volume: 6 mL

Collection Instructions: Send specimen in original tube. Do not aliquot.


Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood ACD Refrigerated (preferred) 6 days YELLOW TOP/ACD
  Ambient  6 days YELLOW TOP/ACD

Reference Values

PHOSPHOMANNOMUTASE

Normal >350 nmol/h/mg protein

 

PHOSPHOMANNOSE ISOMERASE

Normal >1,300 nmol/h/mg protein

Day(s) Performed

Preanalytical processing: Monday through Saturday

Assay performed: Twice per month

CPT Code Information

82657

Method Description

Leukocytes are harvested from one 7-mL tube of ACD-treated blood and the resulting leukocyte cell pellet is subjected to 1 freeze-thaw cycle. The lysate is collected and the enzymatic activity for both phosphomannomutase and phosphomannose isomerase is measured by a colorimetric assay.(Personal communication. Dr. Otto van Diggelen, Erasmus University, Rotterdam, The Netherlands 2008; Cowan T, Pasquali M. Laboratory investigations of inborn errors of metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw Hill Education; 2017:1139-1158)

Reject Due To

Gross hemolysis Reject

Method Name

Colorimetric

Forms

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 a Biochemical Genetics Test Request (T798) with the specimen.

Genetics Test Information

Congenital disorders of glycosylation (CDG) are a large and growing group of inborn errors of glycan metabolism that are clinically diverse, but most often present during infancy or childhood.

 

A diagnostic workup for a CDG should begin with transferrin analysis by liquid chromatography-mass spectrometry (CDG / Carbohydrate Deficient Transferrin for Congenital Disorders of Glycosylation, Serum).

 

Follow-up testing of an abnormal type 1 CDG transferrin isoform profile may include enzymatic analysis for the diagnosis of phosphomannomutase-2 deficiency (PMM2-CDG) and phosphomannose isomerase deficiency (MPI-CDG).

Testing Algorithm

For more information see Congenital Disorders of Glycosylation: Screening Algorithm.