PSAP-related Disorders: PSAP Gene Sequencing

Condition Description

The PSAP gene (10q22.1) codes for a glycoprotein called prosaposin (pSap).  Prosaposin is a precursor for four saposins proteins (Saps) A-D.  Mutations in the PSAP gene can affect either the entire pSap protein or one of the Sap proteins.  All of the conditions caused by mutations in the PSAP gene are inherited in an autosomal recessive manner.  Combined saposin deficiency, also known as prosaposin deficiency, is caused when loss of prosaposin results in deficiency of saposins A-D, usually due to two loss of function mutations in the PSAP gene.  PSAP-related disorders are clinically and metabolically variable neonatal condition characterized by an acute generalized neurovisceral dystrophy and caused by the storage of multiple sphingolipids.   SapA deficiency results in atypical Krabbe.  SapB deficiency results in metachromatic leukodystrophy.  SapC deficiency results in atypical Gaucher disease.  There are currently no known human diseases caused by loss of SapD alone. 

References: 
  • Kuchar et al. (2009), Am; J Med Genet Part A, 149A:613-621.
  • OMIM #176801: PSAP gene
  • OMIM #611721: Combined saposin deficiency
  • OMIM #611722: Atypical Krabbe due to saposin A deficiency
  • OMIM #249900: Metachromatic leukodystrophy due to saposin B deficiency
  • OMIM #610539: Atypical Gaucher disease due to saposin C deficiency

Genes (1)

Your search may have returned a result for a gene alias. Click here for a full list of genes and their aliases.

Indications

This test is indicated for:

  • Confirmation of a clinical/biochemical diagnosis of PSAP-related disorders
  • Carrier testing in adults with a family history of PSAP-related disorders

Methodology

PCR amplification of 14 exons contained in the PSAP gene is performed on the patient's genomic DNA. Direct sequencing of amplification products is performed in both forward and reverse directions, using automated fluorescence dideoxy sequencing methods. The patient's gene sequences are then compared to a normal reference sequence. Sequence variations are classified as mutations, benign variants unrelated to disease, or variations of unknown clinical significance. Variants of unknown clinical significance may require further studies of the patient and/or family members. This assay does not interrogate the promoter region, deep intronic regions, or other regulatory elements, and does not detect large deletions.

Detection

Clinical Sensitivity: Unknown. Mutations in the promoter region, some mutations in the introns and other regulatory element mutations cannot be detected by this analysis. Large deletions will not be detected by this analysis. Results of molecular analysis should be interpreted in the context of the patient's clinical and/or biochemical phenotype.

Analytical Sensitivity: ~99%

Specimen Requirements

Listed below are EGL's preferred sample criteria. For any questions, please call 470.378.2200 and ask to speak with a laboratory genetic counselor (eglgc@egl-eurofins.com).
Submit only 1 of the following specimen types
Whole Blood (EDTA)
WBP

Requirements
EDTA (Purple Top)
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Collection and Shipping
Ship sample at room temperature for receipt at EGL within 72 hours of collection. Do not freeze.
DNA, Isolated
DNA

Requirements
Microtainer
8µg
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Collection and Shipping
Refrigerate until time of shipment in 100 ng/µL in TE buffer. Ship sample at room temperature with overnight delivery.
Saliva
SLV

Requirements
Oragene™ Saliva Collection Kit
Orangene™ Saliva Collection Kit used according to manufacturer instructions. Please contact EGL for a Saliva Collection Kit for patients that cannot provide a blood sample.
Collection and Shipping
Please do not refrigerate or freeze saliva sample. Please store and ship at room temperature.

Special Instructions

Submit copies of diagnostic biochemical test results with the sample, if appropriate. Contact the laboratory if further information is needed.
  • Krabbe Disease: Full Gene Sequencing & Deletion/Duplication
  • Krabbe Disease: Galactocerebrosidase Activity, Dried Blood Spot
  • Gaucher Disease: Biomarker Panel (ACE, CHITO, TRAP)
  • Gaucher Disease: GBA Full Gene Sequencing & Common Mutation Panel
  • Gaucher Disease: Angiotensin Converting Enzyme (ACE)
  • Gaucher Disease: Chitotriosidase (CHITO)
  • Gaucher Disease: Tartrate Resistant Acid Phosphatase (TRAP)
  • Gaucher Disease: Enzyme Assay
  • Metachromatic Leukodystrophy: Full Gene Sequencing & Deletion/Duplication
  • Metachromatic Leukodystrophy
  • Custom diagnostic mutation analysis (KM) is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.
  • Prenatal testing is available to adult couples who are confirmed carriers of mutations. Please contact the laboratory genetic counselor to discuss appropriate testing prior to collecting a prenatal specimen.

How to Order