Facioscapulohumeral Muscular Dystrophy 1B; FSHMD1B
Facioscapulohumeral muscular dystrophy type 1B (FSHD1B or FSHMD1B) is a much rarer type, occurring in several dozen well documented families. The incidence of FSHD1B is not known at this time, but is unlikely to exceed 2% of all cases of FSHD. In FSHD1B the disease is NOT associated with the deletion of 3.3-kb repeats from a chromosomal tandem repeat called D4Z4 located near the end of chromosome 4 at the 4q35-qter location. FSHD1B may be caused by different genes, located on the same or different chromosomes.
FSHD1B may also be caused by proximal and distal deletions that extend into D4Z4 that cause the standard genetic test to be “negative” even though the patient has the requisite number of deletions to cause FSHD. FSHD1B is also referred to as non-chromosome 4 linked FSHD. A common misconception is that FSHD1B is linked to the D4Z4 that is also present on the sub-telomere of chromosome 10. In fact, however, a shortened D4Z4 repeat on 10q26 does not cause FSHD or have anything to do with FSHD1B.
The online database Online Mendelian Inheritance in Man (OMIM) is an excellent source for further information on the science and medicine of FSHD 1B. OMIM was designed for use by physicians and other professionals concerned with genetic disorders, by genetics researchers, and by advanced students in science and medicine. OMIM is developed and maintained by the National Center for Biotechnology Information (NCBI). This database is a catalog of human genes and genetic disorders and has hyperlinks to MEDLINE and sequence records in the Entrez system, and links to additional related resources at NCBI and elsewhere.
To see the Online Mendelian Inheritance in Man pages on facioscapulohumeral muscular dystrophy 1B; FSHMD1B please click HERE.
