Molecular Diagnostics

Molecular Genetics

Section Chief: Jeffrey A. Kant, MD, PhD

Through the PGI/CLSI Federated Diagnostic Molecular Genetics Laboratory, the Pittsburgh Genetics Institute (PGI) and the Division of Molecular Diagnostics offer molecular genetics testing for several hereditary diseases, including cystic fibrosis, Gaucher disease, Duchenne muscular dystrophy, and myotonic dystrophy. Tests are also being developed to screen for cancer succeptibility genes in familial cancers, including breast and colon cancer.

Select this link for information regarding specific tests performed by the Molecular Genetics Laboratory, including a full list of tests, consultation contacts, and details for specimen preparation and delivery.

See below for more general information about the techniques used by the Molecular Genetics Laboratory.

Molecular diagnostic assays provide the most direct approach to determine whether an individual carries a disease-associated gene mutation. These tests are particularly well-suited to prenatal diagnosis, presymptomatic diagnosis, carrier detection, and genetic screening because they are not dependent on manifestation of disease symptoms.

It is important that patients and families understand the purpose, limitations, and implications of molecular diagnostic testing so they can make informed choices about options available to them. The PGI recommends that all patients and family members receive genetic counseling prior to and following molecular diagnostic testing.

Cystic fibrosis

Cystic fibrosis is one of the most common genetic diseases in the United States. The incidence of cystic fibrosis in North American Caucasians of European ancestry is one in 2,500, and the carrier frequency is one in 25. Mutations in both alleles of the CFTR gene cause the clinical symptoms of cystic fibrosis, which include pancreatic insufficiency, chronic pulmonary disease, and an increase in concentration of sweat electrolytes. More than 300 CFTR mutations have been identified; however, a single mutation (F508) accounts for approximately 70% of the cystic fibrosis alleles.

Molecular diagnostic testing for CFTR mutations complements the sweat test, which has been available for some time for confirmation of clinical diagnosis. Mutation analysis may provide insight, for example, when a patient is suspected of having cystic fibrosis but is too young to undergo a reliable sweat test. Indications for testing include clinical symptoms of cystic fibrosis, a family history of cystic fibrosis, and certain ethnic backgrounds.

The Molecular Genetics Laboratory offers analysis of 14 CFTR mutations, identifying approximately 84% of the mutations associated with cystic fibrosis in the Caucasian population. Analysis for a subset of five of the 14 CFTR mutations is also available and is recommended for Jews of Eastern European descent (Ashkenazi Jews). These account for about 97% of the CFTR mutations among Ashkenazi Jews and 75% of the mutations among non-Ashkenazi Jews and the general Caucasian population.

Gaucher disease

Gaucher disease refers to a group of recessive lysosomal storage disorders caused by mutations in the glucocerebrosidase (GC) gene. Gaucher disease occurs in all ethnic groups but is most common in the Ashkenazi Jewish population, among whom the incidence is approximately one in 450, and the carrier frequency is one in 10. More than 30 mutations in the GC gene have been identified; however, the most prevalent mutation (N370S) occurs in approximately 70% of patients with Gaucher disease.

Molecular diagnostic testing for Gaucher disease complements the glucocerebrosidase activity assay and may be used, for example, to clarify the finding of intermediate GC activity or to guide the choice of therapeutic regimen. Mutation analysis is the method of choice for determination of carrier status.

The Molecular Genetics Laboratory offers analysis of four GC mutations. These four account for approximately 96% of the disease-associated GC mutations among Ashkenazi Jews and approximately 50% of the mutations in the general or non-Ashkenazi population.

Muscular dystrophy

Duchenne muscular dystrophy is the most common dystrophinopathy and presents in early childhood with proximal weakness and serum CK levels over 10,000 IU/L. Duchenne is a lethal, progressive disease that accounts for the majority of cases of myopathy in young boys. Becker is a milder form of muscular dystrophy that follows a clinical course similar to that of Duchenne but at a slower rate. Becker muscular dystrophy can present at any time from childhood to middle age and is associated with a range of symptoms, including hyperCKemia, proximal muscle weakness, easy fatigue, myoglobinuria, and muscle cramps.

Duchenne and Becker are X-linked recessive disorders with an incidence of approximately one in 3,500 male births. Approximately 8% to 10% of female carriers exhibit primary myopathy and hyperCKemia typical of either Duchenne or Becker muscular dystrophy in males.

Molecular diagnostic tests available through the Molecular Genetics Laboratory complement muscle biopsy immunofluorescence assays for disease diagnosis. Molecular diagnostic testing also is used for prenatal diagnosis and to detect carrier status. Tests include direct mutation analyses, linkage studies, and (for female carriers) studies of X-inactivation.

Indications for molecular diagnostic testing include symptoms of muscular dystrophy or a family history of Duchenne or Becker muscular dystrophy.

Professional consultation concerning appropriate testing for individual patients is available by contacting Jeffrey A. Kant, MD, PhD, or Amy Mank-Seymour, MS, Genetics Counselor, at (412) 648-8519.
For additional information on dystrophin gene testing, call Eric Hoffman, PhD, at (412) 648-9549.
For information on familial cancer screening, call John Mulvihill, MD, at (412) 624-9951.
(For more information about the tests performed by the Molecular Genetics Laboratory, please click here.)

The test(s) is (are) performed under an agreement with Roche Molecular Systems, Inc.