MOCS2 SEQUENCING FOR MOLYBDENUM COFACTOR DEFICIENCY - F
Label Name: MOCS2 MOLYBD
Lab Discipline: Molecular Diagnostics
Institution:  Duke University Health System 
EAP ID:  LAB6670 
Last Review:  3/27/2017 10:25:33 PM
Container & Volume
  Age Group   Container   Volume  
  0  - 18 Years LAVENDER TOP TUBE 3  ML
Label Reminders
  Be sure to include patient's name, history #, date and time of collection, and collector's initials.
Collection Notes
  All:
  • Peripheral Blood: One lavender-top EDTA tube (minimum of 3 mls) is required for testing. Forward unprocessed peripheral blood promptly to the laboratory at ambient temperatures. THE SPECIMEN CANNOT BE FROZEN. GREEN-TOP (HEPARIN) TUBES ARE NOT ACCEPTABLE FOR TESTING.

    Amniocytes: 2-4ml of amniotic fluid is required. Forward promptly at ambient temperature only. Contact the Laboratory for additional information and instructions on sample requirements and shipping instructions. SPECIMEN CANNOT BE FROZEN.

    Cultured amniocytes / fibroblasts: Please contact the Laboratory for sample requirements and shipping instructions.

 
Transport
  Please deliver to lab at ambient temperature. If there is a delay of more than 24 hours in delivery, please refrigerate the sample. DO NOT FREEZE!
Turn Around Time -  Routine: 14-28 days   Stat: STAT is Unavailable
Reference Values


MOCS2 MOLYBD



No Reference Values
Methodology
  This assay uses PCR amplification followed by Sanger DNA sequencing to detect mutations in the MOCS2 gene that cause molybdenum cofactor deficiency complementation group B. The coding sequences and flanking intronic sequences (minimum of 20 base pairs) of the MOCS2 gene are amplified from purified genomic DNA by PCR. The primers used for PCR contain M13 universal primer "tails" at their 5' ends, and have 3' ends that are homologous to their genomic target sequence. PCR products are treated with an exonuclease/phosphatase mixture (ExoSAP-IT) and sequenced using universal M13 forward and reverse primers (M13 Forward/-20 and M13 Reverse/-27) with the Big Dye Terminator v3.1 Cycle Sequencing Kit. These products are purified with the Big Dye XTerminator Purification Kit and resolved using the ABI 3130xl Genetic Analyzer. Data is analyzed by the ABI Data Collection software v3.0, Sequencing Analysis software 5.2 and SeqScape software v2.6.

This test was developed and its performance characteristics determined by the DUHS Clinical Molecular Diagnostics Laboratory. It has not been cleared or approved by the U.S. Food and Drug Administration. This test is used for clinical purposes. It should not be regarded as investigational or for research. This laboratory is certified under the Clinical Laboratory Improvement Amendments of 1988 ("CLIA") as qualified to perform high complexity clinical testing.
   
   
Clinical Significance and Interpretive Data
    BACKGROUND:

Biological activation of molybdenum requires synthesis of molybdenum cofactor. The biosynthesis of molybdenum cofactor requires the products of at least four genes: MOCS1, MOCS2, MOCS3, and GEPH. Molybdenum cofactor is necessary for the function of several important enzymes including sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase. A deficiency in molybdenum cofactor results in severe progressive neurological damage, seizures, feeding difficulties, lens dislocation, mental retardation, neuromuscular problems and usually leads to early childhood death. Molybdenum cofactor deficiency is inherited in an autosomal recessive fashion. At least 42 disease-causing mutations have been identified in the MOCS1, MOCS2, and GEPH genes.

MOCS2 is located on chromosome 5 (5q11) and encodes the large and small subunits of molybdopterin synthase, a heterodimeric enzyme that converts the product of the MOCS1 gene (precursor Z) to molybdopterin. The MOCS2 gene is defective in patients with molybdenum cofactor deficiency, type B. The incidence of molybdenum cofactor deficiency is extremely low (approximately 100 cases reported wordwide. Mutation analysis is important for disease diagnosis. In some cases in which the familial mutations are known, the analysis of one or two exons of the gene may be performed in lieu of full gene sequencing.

CLINICAL SIGNIFICANCE AND UTILITY:

A definitive diagnosis of molybdenum cofactor deficiency can be made through full sequencing of the MOCS2 gene. A definitive diagnosis can aid physicians in correlation of clinical symptoms with a specific genetic defect.

Precise knowledge of the disease causing mutations in an individual can aid in the genetic counseling of parents and family members. Because molybdenum cofactor deficiency is inherited as an autosomal recessive condition, the parents of children with the disease are obligate carriers of the disorder and have a 25% chance with each pregnancy of having another child with the disease. Unaffected siblings of affected individuals have a 2/3 chance of being a carrier for molybdenum cofactor deficiency.

INTERPRETATION:

Coding and flanking intronic sequences are compared to a reference sequence. Sequence changes found in these regions will be reported as (1) known disease-causing mutations, (2) a mutation previously unreported, but of the type expected to cause the disease; i.e. frameshift mutations, nonsense mutations, etc. (3) sequence variation of uncertain clinical significance, or (4) benign polymorphisms. Variants of uncertain clinical significance may require additional studies including gene sequencing of other family members or other functional studies. All sequence changes, with the exception of benign polymorphisms, are confirmed by reamplification and resequencing of the relevant exon(s).

   
Indications
    Patients with clinical symptoms consistent with molybdenum cofactor deficiency as well as individuals with a family history of the disease should be tested. In cases of known familial mutations, amniocytes from an at-risk pregnancy may also be tested.
   
Limitations
    Due to the rarity of molybdenum cofactor deficiency and the lack of comprehensive published MOCS2 DNA mutation analysis data, the residual risk of having an MOCS1 gene mutation that is not detected by the targeted gene sequencing approach used in this assay is unknown. Therefore, the chance that an individual with molybdenum cofactor deficiency has no detectable mutations by gene sequencing cannot be estimated. These results are not intended to be used as sole criteria for clinical diagnosis or patient management decisions and are not a substitute for a physician's judgment and clinical experience. Correlation with other laboratory testing or clinical findings is required.

The sensitivity and specificity of DNA sequencing is high for the detection of nucleotide base changes, small deletions and insertions in the regions analyzed. Only the coding regions of the MOCS1 gene and immediate flanking intronic sequences were examined. Changes in the promoter region, farther into the introns, or in other non-coding regions of the gene, would not be detected. Mutations in genes other than MOCS2 would not be identified. Large deletions, duplications, multiple exon insertions, sequence alterations adversely affecting primer binding, and complete deletion of one allele may not be identified using these methods. Mutations or polymorphisms in the DNA oligonucleotide primer binding regions, poor DNA quality, insufficient DNA quantity or the presence of PCR inhibitors can result in uninterpretable or (rarely) inaccurate results.
   
Test Synonyms
  Synonym(s): MOCOD
Synonym(s): Molybdenum Cofactor Deficiency
Molecular Diagnostics Laboratory
(MDX)

Medical Director:
 Michael Datto, M.D., Ph.D.
 Phone: 919-684-6965
 Email: michael.datto@duke.edu
Lab Director:
 Catherine Rehder Ph.D, FACMG
 Phone: 919-613-8434
 Email: catherine.rehder@duke.edu
Lab Director:
 Siby Sebastian Ph.D., DABMG
 Phone: 919-613-8432
 Email: siby.s@duke.edu

Address: 
 Wadsworth Bldg, Cytogenetics, Rm 0220
 2351 Erwin Rd
 Durham,  NC  27705
 Phone: 919-684-2698
 FAX: 919-668-5424

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