Skeletal Dysplasia Panel

 

Generalized disorders of cartilage and bone have been referred to as skeletal dysplasias. This group of conditions is frequently associated with disproportionate short stature and skeletal abnormalities.

Achondroplasia is one of the most common skeletal dysplasias characterized by short stature, disproportionately short arms and legs, large head and characteristic facial features. This condition is inherited in an autosomal dominant manner with the majority of patient cases arising in a de novo fashion. More than 99% of patients with achondroplasia have one of two mutations in the FGFR3 gene: 1138G>A or 1138G>C (p.Gly380Arg).

Hypochondroplasia is an autosomal dominant skeletal dysplasia also characterized by short stature, short hands and feet, stocky build, disproportionately short arms and legs, mild joint laxity and large head size. The majority of patient cases arise from de novo mutations; and 70% of patients with hypochondroplasia are heterozygous for a mutation in the FGFR3 gene.

Mild cases of achondroplasia and severe cases of hypochondroplasia may have overlapping clinical features and may be confused clinically. Thus, molecular genetic testing is valuable with respect to confirmation of a correct diagnosis.

Thanatophoric dysplasia (TD) is an autosomal dominant short-limb skeletal dysplasia that is usually perinatal lethal and suspected when fetal ultrasound reveals significantly shortened long bones and a narrow thorax. Cloverleaf skull is most frequently seen in type II TD, and occasionally observed in type I TD. Sequence analysis of select regions of the FGFR3 gene has a mutation detection rate of greater than 99%. This testing can be done prenatally to confirm a suspected diagnosis of TD. The majority of affected fetuses have a de novo mutation in the FGFR3 gene.

REASONS FOR REFERRAL:

  • Confirmation of a clinical diagnosis
  • Prenatal genetic testing in fetuses with skeletal abnormalities on ultrasonography
  • Carrier screening for prenatal patients
  • Prenatal genetic testing in a fetus with suspected thanatophoric dysplasia

 

GENETICS CENTER SKELETAL DYSPLASIA TESTING METHODS:

  • Comprehensive Achondroplasia/Hypochondroplasia Panel (FGFR3)
    • Targeted Mutation Analysis for FGFR3 p.Gly380Arg mutation.
    • Sequence analysis of FGFR3 exons 9,13 and 15.
  • Achondroplasia
    • Targeted Mutation Analysis for FGFR3 p.Gly380Arg mutation.
  • Hypochondroplasia
    • Sequence analysis of FGFR3 exons 9, 13 and 15.
  • Thanatophoric dysplasia
    • Sequence analysis of FGFR3 exons 7, 10, 15 and 19.

 

TURN AROUND TIME:

  • Targeted Mutation Analysis: 5 days
  • Sequence Analysis: 10 days
  • For prenatal samples – please contact laboratory to arrange for expedited testing

 

SPECIMEN REQUIREMENTS AND SHIPPING/HANDLING:

  • Blood: A single tube with 1-5 mL whole blood in EDTA (lavender top).
  • Amniotic Fluid: 15 mL of clear amniotic fluid (30 mL if Karyotype is also ordered). The sample also needs to be accompanied by 1-5 mL of maternal blood in EDTA (lavender top) for maternal cell contamination studies.

 

SHIPPING:

Blood Sample: Store blood at 4°C until shipment. Ship at ambient temperature in an insulated container via overnight delivery within 96 hours of collection.
Amniotic Fluid: Store fluid at 4°C until shipment. Ship at ambient temperature in an insulated container via overnight delivery within 4 hours after collection.

Send to:

Genetics Center
211 S. Main Street
Suite AA
Orange, CA 92868
Tel: (714)288-3500

REQUIRED FORMS:

 

TEST LIMITATIONS:

Targeted mutation analysis tests only for the specified mutations. Gene sequence analysis is unable to detect mutations in regions of the gene not examined, which may include promoter regions, introns and additional exons unless otherwise specified. Sequencing may also be unable to detect large deletions and/or insertions and chromosomal rearrangements. It is possible that some patients may carry a rare mutation of this nature not detected by this assay. This assay may detect polymorphisms of unknown clinical significance, which may require further studies.

CPT CODES:

  • Comprehensive Achondroplasia/Hypochondroplasia Panel:
    • CPT’s: 81401, 81404, G0452
  • Achondroplasia:
    • CPT’s: 81401, G0452
  • Hypochondroplasia:
    • CPT’s: 81404, G0452
  • Thanatophoric Dysplasia:
    • CPT’s: 81404, G0452