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Lab Dept:
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Anatomic Pathology
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Test Name:
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PSEUDOACHONDROPLASIA (COMP) SEQUENCING
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General Information
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Lab Order Codes:
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MEDG (Blood or Buccal Swab)
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Synonyms:
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Multiple Epiphyseal Dysplasia (MED) Fairbank or Ribbing Type; EDM1; Spondyloepiphyseal Dysplasia, PSACH
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CPT Codes:
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81406 – Molecular Pathology procedure, Level 7
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Test Includes:
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Using genomic DNA obtained from the submitted biological material, bi-directional sequence of the coding region and splice junctions of exons 8-9 of the COMP gene is analyzed. Mutations found in the first person of a family to be tested are confirmed by repeat analysis using sequencing, restriction fragment analysis or another appropriate method.
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Logistics
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Test Indications:
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Both MED and PSACH are characterized by short limbed dwarfism, identifiable during childhood, with a normal face and head. Skeletal findings in MED include epiphyseal dysplasia, hip dysplasia and degenerative arthritic changes, brachydactyly with shortened metacarpals and phalanges, and hyperextensible finger joints. Findings in PSACH are typically more severe and include lordosis, kyphosis, and scoliosis as well as other vertebral/spinal anomalies and a waddling gait. In addition, brachydactyly and telescoping fingers, ulnar deviation of the wrists; short tubular bones, fragmented epiphyses and irregular mushroomed metaphyses, limited elbow and hip extension, lax ligaments, genu valgum varum, and recurvatum may be seen. Clinical diagnosis in these disorders may be difficult due to the absence of characteristic facial features and the fact that growth retardation may not be apparent until the second year of life. Mutation of the COMP gene, a member of the thrombospondin gene family, under lie both disorders, as they are allelic. Almost all cases of PSACH are thought to be due to mutation in COMP, and approximately 80% of classical MED cases are a result of mutation of this gene. The COMP gene encompasses 19 exons. Exons 4-19, which encode the EGF-like (type II) repeats, calmodulin-like (type III) repeats, and the C-terminal domain, correspond in sequence and intron location to the thrombospondin genes, while exons 1-3 are unique to COMP.
Reasons for referral:
1. Confirmation of clinical diagnosis
2. Identification of patients at risk for early onset arthritic changes
3. Genetic counseling
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Lab Testing Sections:
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Anatomic Pathology - Sendouts
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Referred to:
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GeneDx, Inc. (GDX#: 1311)
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Phone Numbers:
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MIN Lab: 612-813-6280
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STP Lab: 651-220-6550
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Test Availability:
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Daily, 24 hours (Preferred draws are Sunday - Thursday as specimens can only be received at the reference lab Monday - Friday. Specimens collected Friday or Saturday will be held for shipment on Monday.)
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Turnaround Time:
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8-10 weeks for new patients
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Special Instructions:
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A GeneDx request form must be sent with anypatient or specimen to the laboratory.
COMPcan be tested using cells obtained by swabbing the buccal mucosa (inside of cheek). Buccal swab collection kits are available from GeneDx (ph. 301-519-2100). Buccal Kit info link: http://www.genedx.com/buccal_swab_kits.php
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Specimen
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Specimen Type:
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Whole blood
Buccal cell swab (preferred specimen)
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Container:
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Blood: Lavender top (EDTA) tube
Buccal Smear: Cytobrush Plus Cell CollectorŽ kit
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Draw Volume:
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1 - 5 mL blood
2 swabs from the Cytobrush Plus Cell CollectorŽ kit
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Processed Volume:
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Same as Draw Volume
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Collection:
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Routine venipuncture for blood specimens, invert gently to mix
Buccal swab kit for buccal swabs:
Buccal Cell Collection procedure:
1. Remove a swab from the Buccal swab kit touching only the “stick” end.
2. Do Not rinse mouth before starting. Have the individual open his/her mouth. Twirl the swab on the inner cheek for 30 seconds. Do Not scrape so hard that the cheek bleeds.
3. Place the swab end in the labeled tube. Cut the “stick” with scissors at the level of the top of the tube. Replace cap and close completely.
4. Repeat the process with another swab on the opposite cheek.
5. Send the kit to the lab for processing and mailing.
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Special Processing:
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Lab Staff: Send whole blood in original collection container labeled with patient name, date of birth and medical record number, including signed consent form and requisition, with a cool pack, via overnight or second-day courier so that the sample will arrive at GeneDx, Inc. on a weekday (Monday through Friday). Samples drawn on Friday or Saturday should be held at refrigerated temperatures for shipment on Sunday. Do not freeze.
Note: Specimens may be stored at refrigerated temperatures for up to 3 days prior to shipping.
Mail the Cytobrush Plus Cell CollectorŽ kit, including signed consent form and requisition, by regular mail to GeneDx in the included envelope.
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Patient Preparation:
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For buccal cell collection, Do Not have the patient rinse his/her mouth.
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Sample Rejection:
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Unrefrigerated specimens older than 48 hours, clotted or hemolyzed for blood, frozen specimens, mislabeled or unlabeled specimens
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Interpretive
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Reference Range:
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No mutations detected
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Critical Values:
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N/A
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Limitations:
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N/A
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Methodology:
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Bi-directional sequence analysis
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References:
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GeneDx, Inc. July 2008
(301) 519-2100 Fax (301) 519-2892
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Updates:
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2/7/2013: CPT update
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