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Hypomyelinating Leukodystrophy 8 with or without Oligodontia and/or Hypogonadotropic Hypogonadism via the POLR3B 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
POLR3B 81479 81479,81479 $990
Test Code Test Copy Genes Test CPT Code Gene CPT Codes Copy CPT Code Base Price
3805POLR3B81479 81479,81479 $990 Order Options and Pricing

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).

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


  • Li Fan, MD, PhD, FCCMG, FACMG

Clinical Features and Genetics

Clinical Features

POLR3B-related hypomyelinating leukodystrophy is a rare neurological disorder characterized by deficient cerebral myelin formation and cerebellar atrophy with onset between 2 and 4 years old. This disorder was also known as 4H (hypomyelination, hypodontia, hypogonadotropic hypogonadism) leukodystrophy. The major symptoms include gross motor delay or regression before six years old, short stature, tremor-ataxia, spasticity, cerebellar atrophy, unsteady, wide-based gait, myopia, and mild to moderate intellectual disability. Minor features include dysphagia, hypodontia, oligodontia, and hypogonadotropic hypogonadism. MRI image analysis shows diffused hypomyelination and thin corpus callosum.  Phenotype is variable, slowly progressive or nonprogressive (Tétreault et al. 2011. PubMed ID: 22036172; Wolf et al. 2014. PubMed ID: 25339210).  

As hypomyelinating leukodystrophy can be caused by defects in many genes with variable and overlapping presentations, it is difficult to diagnose by clinical manifestation and image studies only. An accurate molecular diagnosis is critical for treatment, prognosis, and prediction of recurrence risk as well as future family planning.


POLR3B-related hypomyelinating leukodystrophy is inherited in an autosomal recessive manner. Pathogenic variants in POLR3B include missense, nonsense, splicing, and small deletions. Large deletions have also been reported in the POLR3B locus (Human Gene Mutation Database). De novo pathogenic variants are not common.

POLR3B encodes the second largest subunit B of RNA polymerase III, which is responsible for the transcription of transfer RNAs (tRNAs) and a large array of other small non-coding RNAs (Tétreault et al. 2011. PubMed ID: 22036172). A mouse model with a homozygous Polr3b c.308G > A (p.Arg103His) variant resulted in embryonic lethality and malfunction of RNA polymerase III biogenesis (Choquet et al. 2019. PubMed ID: 31221184). POLR3B is relatively intolerant to missense variants (Genome Aggregation Database). POLR3B has been cited as an essential gene for growth of human tissue culture cells (Online Gene Essentiality, ogee.medgenius.info).

Clinical Sensitivity - Sequencing with CNV PGxome

Pathogenic variants in POLR3B are considered one of the major causes of hypomyelinating leukodystrophies. In 37 patients with hypomyelinating leukodystrophies, all had pathogenic variants either in POLR3A (27 cases) or in POLR3B (10 cases; Daoud et al. 2013. PubMed ID: 23355746, Bernard et al. 2011. PubMed ID: 21855841, Tétreault et al. 2011. PubMed ID: 22036172, Potic et al. 2012. PubMed ID: 22451160).

Testing Strategy

This test is performed using Next-Gen sequencing with additional Sanger sequencing as necessary.

This test provides full coverage of all coding exons of the POLR3B 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

POLR3B sequencing is recommended for patients who are suspected to have hypomyelinating leukodystrophy. Targeted testing is indicated for family members of patients who have known pathogenic variants in POLR3B. This test may also be considered for the reproductive partners of individuals who carry pathogenic variants in POLR3B.


Official Gene Symbol OMIM ID
POLR3B 614366
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT


  • Bernard et al. 2011. PubMed ID: 21855841
  • Choquet et al. 2019. PubMed ID: 31221184
  • Daoud et al. 2013. PubMed ID: 23355746
  • Genome Aggregation Database (gnomAD).
  • Human Gene Mutation Database (Biobase).
  • Potic et al. 2012. PubMed ID: 22451160
  • Tétreault et al. 2011. PubMed ID: 22036172
  • Wolf et al. 2014. PubMed ID: 25339210


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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View Ordering Instructions

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2) Select Additional Test Options

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