Question: How many people are affected by myotonic dystrophy ?
Answer: Myotonic dystrophy affects at least 1 in 8,000 people worldwide. The prevalence of the two types of myotonic dystrophy varies among different geographic and ethnic populations. In most populations, type 1 appears to be more common than type 2. However, recent studies suggest that type 2 may be as common as type 1 among people in Germany and Finland.
Source: GHR

Question: What are the genetic changes related to myotonic dystrophy ?
Answer: Myotonic dystrophy type 1 is caused by mutations in the DMPK gene, while type 2 results from mutations in the CNBP gene. The specific functions of these genes are unclear. The protein produced from the DMPK gene may play a role in communication within cells. It appears to be important for the correct functioning of cells in the heart, brain, and skeletal muscles (which are used for movement). The protein produced from the CNBP gene is found primarily in the heart and in skeletal muscles, where it probably helps regulate the function of other genes. Similar changes in the structure of the DMPK and CNBP genes cause the two forms of myotonic dystrophy. In each case, a segment of DNA is abnormally repeated many times, forming an unstable region in the gene. The mutated gene produces an expanded version of messenger RNA, which is a molecular blueprint of the gene that is normally used to guide the production of proteins. The abnormally long messenger RNA forms clumps inside the cell that interfere with the production of many other proteins. These changes prevent muscle cells and cells in other tissues from functioning normally, which leads to the signs and symptoms of myotonic dystrophy.
Source: GHR

Question: Is myotonic dystrophy inherited ?
Answer: Both types of myotonic dystrophy are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition. As myotonic dystrophy is passed from one generation to the next, the disorder generally begins earlier in life and signs and symptoms become more severe. This phenomenon, called anticipation, has been reported with both types of myotonic dystrophy. However, the evidence for anticipation appears to be strongest in myotonic dystrophy type 1. In this form of the disorder, anticipation is caused by an increase in the length of the unstable region in the DMPK gene. It is less clear whether anticipation occurs in myotonic dystrophy type 2, and the mechanism is unknown. A longer unstable region in the CNBP gene does not appear to influence the age of onset of the disorder.
Source: GHR