CPT® Code 81239

Molecular genetic testing is a critical procedure used to identify abnormal (expanded) alleles and to characterize specific alleles on the DMPK (DM1 protein kinase) gene, which is associated with myotonic dystrophy type 1. The DMPK gene is located on the long (q) arm of chromosome 19 at position 13.32 (19q13.32) and plays a vital role in coding a protein that facilitates communication and impulse transmission between cells in various tissues, including the heart, central nervous system, and skeletal muscles. Myotonic dystrophy type 1 manifests through a range of symptoms, including fatigue, muscle pain, difficulty swallowing, cataracts, cardiac conduction defects, respiratory complications, and male balding and infertility. The disease can be classified into three forms: mild, classic, and congenital. The mild form typically allows individuals to maintain a normal lifespan, with muscle weakness primarily affecting the lower legs, hands, face, and neck, usually beginning around the ages of 20 to 30. The classic form is associated with a shortened lifespan and presents with muscle weakness and wasting, prolonged muscle tensing (myotonia), cataracts, and abnormal cardiac function. The congenital form is the most severe, characterized by generalized hypotonia and muscle weakness at birth, respiratory distress, and a high risk of early death. The DMPK gene features a unique DNA allele with a trinucleotide building block pattern of three amino acids: cysteine, threonine, and glycine (CTG), which typically repeats between 5 to 34 times. However, longer repeats lead to gene instability, resulting in an altered version of messenger RNA that forms clumps within the cells. When the allele contains 35 to 49 CTG repeats, it is classified as a pre-mutation, where individuals remain asymptomatic, but the risk of further expansion increases with each generation. In the mild form, the allele usually has 50 to 100 CTG repeats, while the classic form has 100 to 1000 CTG repeats, and the congenital form has more than 2000 CTG repeats. The CPT® code 81234 is used to report DMP gene analysis for detecting the presence of abnormal, expanded alleles, while CPT® code 81239 is specifically for DMPK gene analysis to determine the characteristics of these expanded alleles, including their size and any similarities or differences.