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Methylmalonic Aciduria and/or Homocystinuria via the CD320 Gene

Summary and Pricing

Test Method

Exome Sequencing with CNV Detection
Test Code Test Copy GenesTest CPT Code Gene CPT Codes Copy CPT Codes Base Price
CD320 81479 81479,81479 $990
Test Code Test Copy Genes Test CPT Code Gene CPT Codes Copy CPT Code Base Price
8773CD32081479 81479,81479 $990 Order Options and Pricing

Pricing Comments

Our favored testing approach is exome based NextGen sequencing with CNV analysis. This will allow cost effective reflexing to PGxome or other exome based tests. However, if full gene Sanger sequencing is desired for STAT turnaround time, insurance, or other reasons, please see link below for Test Code, pricing, and turnaround time information.

An additional 25% charge will be applied to STAT orders. STAT orders are prioritized throughout the testing process.

Click here for costs to reflex to whole PGxome (if original test is on PGxome Sequencing platform).

Click here for costs to reflex to whole PGnome (if original test is on PGnome Sequencing platform).

The Sanger Sequencing method for this test is NY State approved.

For Sanger Sequencing click here.

Turnaround Time

3 weeks on average for standard orders or 2 weeks on average for STAT orders.

Please note: Once the testing process begins, an Estimated Report Date (ERD) range will be displayed in the portal. This is the most accurate prediction of when your report will be complete and may differ from the average TAT published on our website. About 85% of our tests will be reported within or before the ERD range. We will notify you of significant delays or holds which will impact the ERD. Learn more about turnaround times here.

Targeted Testing

For ordering sequencing of targeted known variants, go to our Targeted Variants page.


Genetic Counselors


  • McKenna Kyriss, PhD

Clinical Features and Genetics

Clinical Features

Methylmalonic aciduria due to defects in the transcobalamin receptor appears to be a rare disorder, with fewer than 10 cases reported to date. Based on current knowledge, the majority of affected individuals have no overt clinical symptoms, although one patient presented in early infancy with bilateral central retinal artery occlusions (Quadros et al. 2010; Karth et al. 2012; Watkins and Rosenblatt 2014). Biochemically, all patients identified to date have been found to exhibit moderately elevated methylmalonic acid in plasma and/or urine, and most have also been found to have elevated serum homocysteine levels (Quadros et al. 2010; Karth et al. 2012). All patients identified in the study by Quadros et al. (2010) were also found to have elevated levels of C3-acylcarnitine. Additionally, the index patient reported by Quadros et al. (2010) was found to have elevated vitamin B12 in the plasma by 9 months of age.

To date, none of the identified patients have shown the hematological or neurological symptoms that are often associated with cobalamin deficiency, but the long-term outcome of this disorder is not currently known. While it is possible this may be primarily a benign disorder, patients with CD320 variants may be identified by newborn screening programs and flagged for follow up studies. In individuals with pathogenic variants in the CD320 gene, treatment with pharmacological doses of vitamin B12 has been shown to lower methylmalonic acid and homocysteine to normal levels, and thus it may be important to distinguish such individuals from those with the more clinically severe intracellular cobalamin deficiency disorders (Quadros et al. 2010).


Current knowledge of the transcobalamin receptor deficiency disorder suggests that this is an autosomal recessive disorder, and CD320 is the only gene known to be involved. To date, only a single variant has been reported in this gene (p.Glu88del), and all affected patients have been reported to be homozygous for this variant (Quadros et al. 2010; Karth et al. 2012).

Cobalamin is transported to different tissues in the body via the bloodstream, while bound to the protein transcobalamin. The transcobalamin cobalamin receptor is a glycoprotein found on the plasma membrane of cells. The receptor has a large extracellular domain, a single transmembrane domain, and a cytoplasmic domain, and is responsible for mediating the uptake of transcobalamin-bound cobalamin into cells. The Glu88 amino acid is located in the extracellular domain of this protein, in the region thought to be directly involved in interacting with transcobalamin (Quadros et al. 2010; Karth et al. 2012; Watkins and Rosenblatt 2014).

Clinical Sensitivity - Sequencing with CNV PGxome

At this time, the sensitivity of this test is difficult to estimate due to the low number of cases reported in the literature. Analytical sensitivity may be high as the only reported causative variant is detectable by sequencing.

Testing Strategy

This test provides full coverage of all coding exons of the CD320 gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).

Indications for Test

Individuals with elevated methylmalonic acid and no identified defects in other genes known to cause methylmalonic aciduria are good candidates for this test, particularly if they also have elevated C3-acylcarnitine levels, and possibly elevated homocysteine levels. Family members of patients who have known pathogenic CD320 variants are candidates. We will also sequence the CD320 gene to determine carrier status.


Official Gene Symbol OMIM ID
CD320 606475
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

Related Tests

Homocystinuria, cblE Type, via the MTRR Gene
Homocystinuria, cblG Type, via the MTR Gene
Methylmalonic Aciduria and Homocystinuria, cblD Type, via the MMADHC Gene


  • Karth P. et al. 2012. Journal of Aapos : the Official Publication of the American Association For Pediatric Ophthalmology and Strabismus / American Association For Pediatric Ophthalmology and Strabismus. 16: 398-400.  PubMed ID: 22819238
  • Quadros E.V. et al. 2010. Human Mutation. 31: 924-9.  PubMed ID: 20524213
  • Watkins and Rosenblatt. 2014. Inherited Disorders of Folate and Cobalamin Transport and Metabolism. In: Valle D, Beaudet A.L., Vogelstein B, et al., editors. New York, NY: McGraw-Hill. OMMBID.


Ordering Options

We offer several options when ordering sequencing tests. For more information on these options, see our Ordering Instructions page. To view available options, click on the Order Options button within the test description.

myPrevent - Online Ordering

  • The test can be added to your online orders in the Summary and Pricing section.
  • Once the test has been added log in to myPrevent to fill out an online requisition form.
  • PGnome sequencing panels can be ordered via the myPrevent portal only at this time.

Requisition Form

  • A completed requisition form must accompany all specimens.
  • Billing information along with specimen and shipping instructions are within the requisition form.
  • All testing must be ordered by a qualified healthcare provider.

For Requisition Forms, visit our Forms page

If ordering a Duo or Trio test, the proband and all comparator samples are required to initiate testing. If we do not receive all required samples for the test ordered within 21 days, we will convert the order to the most effective testing strategy with the samples available. Prior authorization and/or billing in place may be impacted by a change in test code.

Specimen Types

Specimen Requirements and Shipping Details

PGxome (Exome) Sequencing Panel

PGnome (Genome) Sequencing Panel

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Note: acceptable specimen types are whole blood and DNA from whole blood only.
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