Last Modified:
5/18/2018 7:00:40 AM
Client Notes:
Contact the Laboratory at 66-1500 (Option 1) for the Payment requirements of this test.
Specimen Requirements:
Two - 3.0 to 5.0 mL in Whole Blood in a Lavender Top Tubes - EDTA
Pediatric requirements: 1.0 to 2.0 mL Whole Blood in a Lavender Top Tube - EDTA
Transport & Storage: Temperature/Stability:
Refrigerated
Reference Range:
Not Applicable
Methodology:
Bi-directional sequence analysis
Clinical Significance:
Holoprosencephaly (HPE) is etiologically heterogeneous, with genetic factors, maternal host factors, and possible environmental factors contributing. Chromosome anomalies underlie up to half of HPE, including trisomy of chromosomes 13 or 18, and various structural anomalies of several chromosomes. Submicroscopic deletion involving HPE-related genes have been identified by FISH in another 5% of individuals with HPE [Muenke, unpublished]. Approximately 18-25% of individuals with HPE associated with a single-gene disorder have a recognizable syndrome (e.g. Pallister-Hall syndrome, Smith-Lemli-Opitz syndrome), while the remainder have HPE not associated with a recognizable syndrome. Of the nonsyndromic HPE patients, the literature suggests that approximately 13% of patients will be found to have a mutation in the SHH, TGIF, SIX3, or ZIC2 gene, which usually behave in an autosomal dominant manner.
Bi-directional sequence analysis of four genes involved in holoprosencephaly is offered by GeneDx as follows. Using genomic DNA obtained from the submitted sample, bi-directional DNA sequence of most of the coding portion of the SHH gene (3 exons), the TGIF gene (3 exons), the SIX3 gene (2 exons), and the ZIC2 gene (3 exons) is obtained and analyzed. Carrier testing in other family members and prenatal diagnosis is available once the mutation in a family has been defined. Due to the possibility of complete deletion of one copy of any of these genes in association with holoprosencephaly, CopyDx analysis to detect copy number is being developed for patients in whom no heterozygous positions are identified on sequence analysis. Call for further information.
Custom Panel:
No
PRODUCTION SCHEDULE
Days Performed:
Monday, Tuesday, Wednesday, Thursday, Friday
Other Testing Facility:
Gene Diagnostics
PHL Test Code:
MSOT
EPIC Test Code:
Included Tests:
SHH (sonic hedgehog); SIX3 ( homolog of Drosophila So); TGIF (TG-interacting factor); ZIC2 (homolog of Drosophila Opa)
CPT Coding:
83891
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