Clinical and genetic analysis of the first known Asian family with myotonic dystrophy type 2

Abstract

Myotonic dystrophy type 2 (DM2) is more common than DM1 in Europe and is considered a rare cause of myotonic dystrophies in Asia. Its clinical course is also milder with more phenotypic variability than DM1. We herein describe the first known Asian family (three affected siblings) with DM2 based on clinical and genetic analyses. Notably, two of the affected siblings were previously diagnosed with limb-girdle muscular dystrophy. Myotonia (the inability of the muscle to relax) was absent or only faintly present in these individuals. The third sibling had grip myotonia and is the first known Asian DM2 patient. The three DM2 siblings share several systemic characteristics, including late-onset, proximal-dominant muscle weakness, diabetes, cataracts and asthma. Repeat-primed PCR across the DM2 repeat revealed a characteristic ladder pattern of a CCTG expansion in all siblings. Southern blotting analysis identified the presence of 3400 repeats. Further DM2 studies in Asian populations are needed to define the clinical presentation of Asian DM2 and as yet unidentified phenotypic differences from Caucasian patients.

Sporadic Myotonic Dystrophy Type 2 in a Japanese Patient

“…In Japan, only three DM2 patients from one family have been reported ( 10 , 11 ). Our patient differs from these three in several respects.…”

“…Thus far, only three families with DM2 have been identified in Japan. One family was reported in two studies ( 10 , 11 ), while two others were reported at meetings of the Japanese Society of Neurology, albeit recorded only as abstracts with no details available ( 12 , 13 ), suggesting its rarity in comparison to Europe.…”

The current status of medical care for myotonic dystrophy type 1 in the national registry of Japan

“…Myotonic dystrophy is classified as type 1 (DM1) or type 2 (DM2), based on the causative gene. DM1 is far more common in Japan, where DM2 has rarely been reported 1,2 . DM1 is characterized by muscle symptoms, such as myotonia and muscle wasting.…”

“…DM1 is far more common in Japan, where DM2 has rarely been reported. 1,2 DM1 is characterized by muscle symptoms, such as myotonia and muscle wasting. However, it is a systemic disease with cardiac conduction defects, central nervous system involvement, endocrine and metabolic abnormalities, and cataracts.…”