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The Kleberg Cytogenetics Laboratory offers a fluorescence in situ hybridization (FISH)-based assay for identifying the deletion on chromosome 15q11-q13 associated with Prader-Willi syndrome. Clinical Features:Prader-Willi syndrome is characterized by neonatal hypotonia and difficulties feeding. Later on, Prader-Willi syndrome presents with hyperphagia, which can lead to obesity, small hands and feet, hypogonadism, and mental retardation. Reasons for Referral:Patients with clinical features suggestive of Prader-Willi syndrome may be tested for deletions of 15q11-q13 by FISH simultaneously with high-resolution chromosomal analysis (if not previously performed). FISH may also be indicated when methylation studies have shown deficiency of the paternal unmethylated allele. Prenatal diagnosis may be performed if an affected family member has been studied in our laboratory and shown to have a deletion detectable by FISH. Please call regarding all prenatal samples. Testing Methodology:FISH is the application of fluorescently labeled DNA molecules to metaphase chromosomes and interphase nuclei for the detection of chromosome abnormalities and alterations. It is a rapid, reliable and direct approach for identifying patients with microdeletions or microduplications. FISH analysis for Prader-Willi syndrome is performed on metaphase chromosomes. The absence of a hybridization signal indicates a deletion. Approximately 70% of Prader-Willi syndrome patients demonstrate a deletion of 15q11-q13. Interestingly, 30% of patients who do not demonstrate a deletion have inherited two copies of a maternal chromosome 15 and have failed to inherit a paternal chromosome 15. This phenomenon is termed maternal uniparental disomy (UPD). Recently, a methylation assay was developed to identify all deletion and UPD patients with Prader-Willi syndrome, although methylation studies do no distinguish these two types. For individuals who have mental retardation and have not had a chromosome analysis, the current recommendations are routine cytogenetics and FISH, which can be performed simultaneously. For patients who have had a normal karyotype in the past, the methylation assay (see Prader-Willi syndrome DNA Analysis ) can be used to detect most cases of Prader-Willi syndrome. Specimen Requirements:Whole blood in sodium heparin (green-top) tubes: Shipping and Handling:All tubes must be labeled with the patient's testname and date of birth, and a completed requisition form must accompany each sample. If the laboratory is billing the patient's insurance, please enclose a copy of the insurance card. Ship specimens for overnight delivery at ambient temperature. Please notify the laboratory of incoming samples. Turnaround Time:7-10 days CPT Codes and Prices:88230, 88273, 88271, 88291 References:1. Kuwano, et al. (1992) Hum. Mol. Genet. 1: 417-425. Forms: >> Cytogenetics
Requisition Test Code:8476 |