Prader-Willi Syndrome: (15q11q13) FISH Analysis

Turnaround Time

28 days; 7 day rush for infants

CPT Code(s)

88275, 88273, 88271, 88291

Cost

$584

Chromosomes

• Prader-Willi syndrome

Prader-Willi syndrome is characterized by significant infantile hypotonia and feeding difficulties. In early childhood this transitions into excessive eating and morbid obesity. Developmental delay and behavioral problems are common features. Physical characteristics include hypogonadism, short stature, small hands and feet, almond shaped eyes, and hypopigmentation. Prader-Willi syndrome is caused by the lack of expression of the paternally derived region of chromosome 15 (15q11.2-q13). This lack of expression can be caused by a deletion of the paternal chromosome, maternal uniparental disomy (UPD) of chromosome 15 or more rarely, a defect in the imprinting region. Angelman syndrome is characterized by significant developmental delay or intellectual disability, severe speech impairment, an ataxic gait, and inappropriate happy behavior including excessive laughing and smiling. Other physical concerns include microcephaly, seizures, wide mouth and a prominent mandible.

Fluorescence in situ hybridization is a molecular cytogenetic technique in which fluorescently labeled DNA probes are hybridized to metaphase spreads or interphase nuclei. Applications include identification of structurally abnormal chromosomes, including identification of marker chromosomes, detection of very small deletions (microdeletions), and rapid detection of Down syndrome and other numerical chromosome abnormalities; and the rapid detection of sex chromosomes and the SRY gene. FISH should be used in conjunction with G-banded chromosome analysis. FISH is performed upon request when a specific numerical or structural abnormality or microdeletion is suspected. FISH is also utilized to confirm microdeletions identified during high resolution chromosome analysis and to aid in identification of abnormal chromosomes.

Blood is the accepted specimen type for this test. 5-7 ml of whole blood in a green top (sodium heparin) tube is needed for this test. For newborns and small infants, 2-3 ml of blood in a sodium heparin, green top tube is acceptable. Prenatal testing will be considered on a case-by-case basis. Please contact the laboratory prior to sending a prenatal specimen to discuss your case with a lab genetic counselor.

Specimen should be kept at room temperature; do not freeze or refrigerate. Specimen should be sent by courier or overnight mail to arrive at the laboratory the next day.

Considered on a case-by-case basis. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for most prenatal testing. Contact the laboratory prior to sending a prenatal specimen.