CHARCOT-MARIE-TOOTH DISEASE TYPE 1A (CMT1A)
FISH ANALYSIS

The Kleberg Cytogenetics Laboratory offers a fluorescence in situ hybridization (FISH)-based assay for identifying the 1.5 Mb duplication associated with CMT1A.

Clinical Features:

Charcot-Marie-Tooth disease type 1A is an inherited peripheral neuropathy characterized by slowly progressive distal muscle wasting, weakness and decreased nerve conduction velocities. The age of onset of symptoms is variable.

Reasons for Referral:

FISH can be used to detect duplications in patients with a suspected diagnosis of CMT1A or in individuals with a positive family history. Although testing minors for adult onset disorders is not advised, children with neurological symptoms and a first-degree relative with CMT1A may be tested. For accurate interpretation of these results, the affected family member should have a duplication detected by the FISH assay in our laboratory.

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. The majority (>98%) of CMT1A cases are caused by a DNA duplication of a 1.5 Mb region on 17p12 containing the PMP22 gene. The reciprocal product of the CMT1A duplication is a 1.5 Mb deletion that causes hereditary neuropathy with liability to pressure palsies (HNPP). See Inherited Peripheral Neuropathies. FISH for both CMT1A and HNPP is performed on interphase nuclei. In order for a result to be interpreted, at least 70% of the cells must show a consistent hybridization pattern.

Specimen Requirements:

Whole blood in sodium heparin (green-top) tubes:
Adult/Child: Minimum 3.0 -5.0 CC

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:

9 days

CPT Codes and Prices:

88230, 88271, 88273, 88291

References:

1. Lupski, et al. (1993) JAMA 270: 2326-2330
2. Shaffer, et al. (1997) Am. J. Med. Genet. 69: 325-331.

Forms:

>> Cytogenetics Requisition

Test Code:

8462