Joubert Syndrome Type II, DNA Analysis

CPT: 81479
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Test Details

Synonyms

  • Jewish Heritage Test
  • TMEM216

Use

Detect the presence of the R12L mutation (also called R73L) in the TMEM216 gene.

Methodology

Polymerase chain reaction (PCR) and primer extension

Additional Information

Joubert syndrome type II (JBTS2, OMIM 608091) is an inherited, autosomal recessive early-onset disorder characterized by the absence or underdeveloped cerebellar vermis-an area of the brain that controls balance and coördination. This "molar tooth sign" can be seen on midbrain MRI. Common clinical findings in infants are abnormal rapid breathing, hypotonia, oculomotor apraxia/nystagmus, mental retardation, and an inability to coordinate voluntary muscle movements. Other findings include polydactyly, low-set ears, small genitalia, high-arched palate, and hepatic fibrosis. The disease has an elevated prevalence in the Ashkenazi Jewish population, with a carrier rate of 1 in 92. When both parents are carriers of JBTS2, there is a 25% chance with each pregnancy of having a child with the disease. Prenatal diagnosis is available.

Molecular genetic testing for JBTS2 encompasses one mutation in the TMEM216 gene (11q13). Testing for the R12L (also called R73L) mutation identifies approximately greater than 99% of JBTS2 carriers in the Ashkenazi Jewish population. The carrier frequency in the non-Ashkenazi Jewish population has not been determined. A negative result decreases the likelihood that this person is a carrier but cannot completely eliminate the possibility. The presence of a rare mutation cannot be ruled out. DNA test results must be combined with the clinical information for the most accurate interpretation.

Specimen Requirements

Specimen

Whole blood, amniotic fluid, chorionic villus sample (CVS) (Submission of maternal blood is required for fetal testing.), or LabCorp buccal swab kit (Buccal swab collection kit contains instructions for use of a buccal swab.)

Volume

7 mL whole blood, 10 mL amniotic fluid, 20 mg CVS, or LabCorp buccal swab kit

Minimum Volume

3 mL whole blood, 5 mL amniotic fluid, 10 mg CVS, or two buccal swabs

Container

Lavender-top (EDTA) tube, yellow-top (ACD) tube, sterile plastic conical tube or two confluent T-25 flasks for fetal testing, or LabCorp buccal swab kit

Storage Instructions

Maintain specimen at room temperature or refrigerate at 4°C

Causes for Rejection

Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; one buccal swab; wet buccal swab

Clinical Information

References

Edvardson S, Shaag A, Zenvirt S, et al. Joubert syndrome 2 (JBTS2) in Ashkenazi Jews is associated with a TMEM216 mutation. Am J Hum Genet. 2010 Jan; 86(1):93-97.

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
511490 Joubert Syndrome Type II 511491 Joubert Syndrome Type II 41103-3
511490 Joubert Syndrome Type II 511952 PDF 51969-4
511490 Joubert Syndrome Type II 511005 Jewish Heritage Putaway N/A

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