Clinics and Departments

Laboratory Services

Lab Dept:

Anatomic Pathology

Test Name:

PSEUDOACHONDROPLASIA (COMP) SEQUENCING

General Information

Lab Order Codes:

MEDG (Blood or Buccal Swab)

Synonyms:

Multiple Epiphyseal Dysplasia (MED) Fairbank or Ribbing Type; EDM1; Spondyloepiphyseal Dysplasia, PSACH

CPT Codes:

81406 – Molecular Pathology procedure, Level 7

Test Includes:

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.

Logistics

Test Indications:

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

Lab Testing Sections:

Anatomic Pathology - Sendouts

Referred to:

GeneDx, Inc. (GDX#: 1311)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

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.)

Turnaround Time:

8-10 weeks for new patients

Special Instructions:

A GeneDx request form must be sent with any patient or specimen to the laboratory.

Specimen

Specimen Type:

Whole blood

Container:

Lavender top (EDTA) tube

Draw Volume:

1 - 5 mL blood

Processed Volume:

Same as Draw Volume

Collection:

Routine venipuncture for blood specimens, invert gently to mix

Special Processing:

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.

Patient Preparation:

None

Sample Rejection:

Unrefrigerated specimens older than 48 hours, clotted or hemolyzed for blood, frozen specimens, mislabeled or unlabeled specimens

Interpretive

Reference Range:

No mutations detected

Critical Values:

N/A

Limitations:

N/A

Methodology:

Bi-directional sequence analysis

References:

GeneDx, Inc. July 2008
(301) 519-2100 Fax (301) 519-2892

Updates:

2/7/2013: CPT update
5/19/2015: Buccal swabs no longer accepted.



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