Test ID: NPCMS
Niemann-Pick Type C, Full Gene Analysis

Second-tier test for confirming a biochemical diagnosis of Niemann-Pick type C (NPC)

Carrier testing of individuals with a family history of NPC but an affected individual is not available for testing or disease-causing mutations have not been identified

Testing includes full gene sequencing of the NPC1 and NPC2 genes, including analysis for large deletions and duplications.

If skin biopsy is received, fibroblast culture for genetic test will be added and charged separately.

• Molecular Genetics-Biochemical Disorders Patient Information Sheet
• Informed Consent for Genetic Testing

Polymerase chain reaction (PCR) amplification followed by DNA sequencing is utilized to test for the presence of a mutation in the NPC1 and NPC2 genes and  Gene Dosage Analysis by Multiplex Ligation-Dependent Probe Amplification (MLPA)

FBC/80333: Cell Culture

(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc.)

Forms:

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.

2. Molecular Genetics-Biochemical Disorders Patient Information Sheet (Supply T527) in Special Instructions

3. If not ordering electronically, submit a Molecular Genetics Request Form (Supply T245) with the specimen.

Specimen must arrive within 96 hours of collection.

Submit only 1 of the following specimens:

Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

Specimen Volume: 3 mL

Collection Instructions:        

1. Invert several times to mix blood.

2. Send specimen in original tube.

Specimen Stability Information: Ambient (preferred)/Refrigerated

Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask        

Specimen Volume: 1 Full T-75 or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated <24 hours

Specimen Type: Skin biopsy

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin [Supply T115]).

Specimen Volume: 4-mm punch                                                       

Specimen Stability Information: Refrigerated (preferred)/Ambient

No specimen should be rejected. If specimen not received at appropriate temperature or in wrong anticoagulant, include note to laboratory. If questions, contact laboratory.

Niemann-Pick type C (NPC) is an inherited disorder of cholesterol transport that results in an accumulation of unesterified cholesterol and lipids in the lysosomal/endosomal system and in various tissues. Although NPC belongs to a group of lysosomal disorders including Niemann-Pick types A and B, these diseases are metabolically and genetically distinct. Niemann-Pick types A and B are caused by mutations in the SMPD1 gene, which encodes the enzyme sphingomyelinase, whereas NPC is caused by mutations in the NPC1 or NPC2 genes.

The incidence of NPC is approximately 1:120,000 to 1:150,000 live births. Age of onset is variable and ranges from the perinatal period to adulthood. Clinical presentation is also highly variable. Infants may present with or without liver disease (hepatosplenomegaly) and respiratory failure. Those without liver and pulmonary disease may present with hypotonia and developmental delay. Most individuals are diagnosed during childhood with symptoms including ataxia, vertical supranuclear gaze palsy, dystonia, progressive speech deterioration, and seizures resulting in death by the second or third decade of life. Adult-onset NPC is associated with a slower progression and is characterized by neurologic and psychiatric problems.

NPC is inherited in an autosomal recessive manner, in which affected individuals carry 2 mutations in either the NPC1 or NPC2 gene. Most mutations are family specific, although there are 2 mutations in the NPC1 gene which are more common than others. The G992W mutation is common in the French Acadian population of Nova Scotia. The I1061T mutation is the most common mutation worldwide, and is seen in patients of Hispanic and Western European (United Kingdom and France) descent. Full gene sequencing and analysis for large deletions and duplications of the NPC1 and NPC2 genes detect less common disease-causing mutations. 

The recommended first-tier test to screen for NPC is a biochemical test measuring cholesterol esterification coupled with filipin staining on a fibroblast specimen, NIEM/9313 Niemann-Pick Type C Detection, Fibroblasts. Molecular testing provides confirmation of a biochemical diagnosis or a basis for carrier testing of family members. Individuals with abnormal biochemical results are more likely to have 2 identifiable mutations by molecular testing.

An interpretive report will be provided.

An interpretive report will be provided.

A small percentage of individuals who are carriers or have a diagnosis of, Niemann-Pick type C (NPC) disease may have a mutation that is not identified by this method (eg, promoter mutations, deep intronic alterations). The absence of a mutation(s), therefore, does not eliminate the possibility of positive carrier status or the diagnosis of NPC. For carrier testing, it is important to first document the presence of NPC1 or NPC2 gene mutations in an affected family member.

In some cases, DNA alterations of undetermined significance may be identified.

Rare polymorphisms exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.

A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.

In addition to disease-related probes, the multiplex ligation-dependent probe amplification technique utilizes probes localized to other chromosomal regions as internal controls. In certain circumstances, these control probes may detect other diseases or conditions for which this test was not specifically intended. Results of the control probes are not normally reported. However, in cases where clinically relevant information is identified, the ordering physician will be informed of the result and provided with recommendations for any appropriate follow-up testing.

1. NP-C Guidelines Working Group, Wraith JE, Baumgartner MR, et al: Recommendations on the diagnosis and management of Niemann-Pick disease type C. Mol Genet Metab 2009 Sep-Oct;98(1-2):152-65

2. Park WD, O'Brien JF, Lundquist PA, et al: Identification of 58 novel mutations in Niemann-Pick disease type C: correlation with biochemical phenotype and importance of PTC1-like domains in NPC1. Hum Mutat 2003 Oct;22(4):313-325

3. Vanier MT: Niemann-Pick disease type C. Orphanet J Rare Dis 2010 Jun 3;5:16

DNA sequencing is utilized to test for the presence of a mutation in all 25 exons of the NPC1 gene and 5 exons of the NPC2 gene. Gene dosage analysis by multiplex ligation-dependent probe amplification (MLPA) is used to test for the presence of large deletions and duplications within these genes. (Unpublished Mayo method)

Thursday; 10 a.m.

81479- Unlisted molecular pathology procedure