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Achondroplasia

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ACHONDROPLASIA

Gene Symbol: FGFR3

Chromosomal Locus: 4p16.3
 
Protein: Fibroblast growth factor receptor 3 precursor
 
Pseudonyms: ACH
 
TURNAROUND TIME: 8 days
 
AMA 2012: 81401
 
TESTING METHODOLOGY: Detection of a G380R (c.1138G>A or G>C) mutation by PCR and restriction enzyme digestion.
 
SPECIMEN REQUIREMENTS:
  • Collect: Prefer two 5ml whole blood EDTA (lavender top) tube.
  • Min. Collection: 0.7 ml whole blood EDTA.
  • Transport: blood EDTA at Room Temp shipped regular next day air (No Saturday delivery; store specimen at 4°C and ship Monday).
  • Stability: Ambient: up to 7 days; Refrigerated: 2 weeks. Frozen: unacceptable
  • Unacceptable Conditions: Serum. Frozen or severely hemolyzed blood. Clotted blood.
  • Prenatal testing: Direct: 5ml direct unspun amniotic fluid or 15mg CVS tissue with a backup flask growing. Culture: confluent T25 flask. Maternal blood sample is required for maternal cell contamination studies.
A Molecular Genetics Laboratory Test Requisition must accompany the specimen. Contact the Molecular Laboratory at 918-502-1721 to obtain further information.
 
Note: Counseling and informed consent are recommended for genetic testing. A consent form is available as a resource but not required.
 
INTERPRETATIVE DATA:
 
Incidence: 1 in 15,000 to 40,000
 
Inheritance: More than 80% of ACH cases are due to a spontaneous mutation; the remainder are inherited in an autosomal dominant manner with 100% penetrance
 
Disease Characteristics: Achondroplasia is characterized by abnormal bone growth that results in short stature with disproportionately short arms and legs, a large head, and characteristic facial features. In infancy, hypotonia is typical, and development of motor milestones is often delayed. Intelligence and life span are usually normal.
 
Molecular Genetic Mechanism: More than 99% of individuals have a G380R substitution, which may result from a G>A/C point mutation at nucleotide 1138 of the FGFR3 gene.
 
 
Clinical Sensitivity: ~99%
 
Analytic Sensitivity: >99%
 
Test Limitations: Mutations that are not c.1138G>A or G>C will not be detected (less than 1%). Rare diagnostic errors can occur due to primer or probe site mutations or rare polymorphisms.
 
INDICATIONS FOR USE:
  • To confirm the nature of dwarfism in an affected individual.
  • To evaluate fetuses with abnormal ultrasound findings for the possibility of spontaneous Achondroplasia.
  • Individuals at risk who wish prenatal diagnosis.
ADDITIONAL RESOURCES:
 
OMIM Achondroplasia - www.omim.org/entry/100800