The characteristic pattern of weakness is different for DM1 and DM2: In DM1, it is noted in face and jaw muscles, the drooping of the eyelids (ptosis), weakness of the neck muscles, hands and lower legs. DM2 patients commonly present with muscle pain, stiffness, fatigue, or the development of proximal lower extremity weakness (Day & al, 2003). DM1 patients often present with myotonia, disabling distal weakness and severe cognitive problems. Presentation of symptoms varies considerably by form (DM1/DM2), severity and even unusual DM2 phenotypes. It appears to be less significant in type 2 and most current reviews only report mild anticipation as a feature of DM2. Unlike DM1, the size of the repeated DNA expansion does not appear to make a difference in the age of onset or disease severity in DM2. The repeat expansion for DM2 is considerably larger than for DM1, ranging from 75 to over 11,000. The severe congenital form that affects babies in DM1 has not been found in DM2 and the early onset of symptoms is rarely noted to appear in younger patients in the medical literature. While both diseases are considered slow degenerative conditions, DM2 is considered to be generally milder than DM1. Further forms of myotonic dystrophy (DM3, DM4, DMX) are currently suspected by researchers to exist. DM1 also has a congenital form that can severely affect babies and a childhood onset form. There are currently two known types of adult onset DM: Myotonic dystrophy type 1 (DM1), also known as Steinert's disease, and Myotonic dystrophy type 2 (DM2), commonly referred to as PROMM or proximal myotonic myopathy. Myotonic dystrophy is the most common form of adult onset muscular dystrophy and the second most common form of any skeletal muscle disease after Duchenne muscular dystrophy.
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