How is FSHD inherited?

FSHD is a dominantly inherited disease.  This means that inheriting one defective copy of a segment of DNA from a parent with FSHD is sufficient to cause disease. The genetic defect in FSHD occurs on one end of chromosome number 4.  All individuals carry two copies of their DNA in each cell but pass on a single copy to their offspring. A parent with FSHD will carries the FSHD genetic defect on one of two copies of chromosome 4 as illustrated in red in the diagram below.  Therefore an affected parent has a 50:50 chance of passing on the defective copy to their child as illustrated in the diagram below.  

Dominant Inheritance

There are exceptions, however, to this pattern of inheritance. In up to 30% of cases of individuals with FSHD, no signs of FSHD are detected in the parents and genetic testing shows no defect on chromosome 4.  Such a situation, known as sporadic FSHD, means that the FSHD genetic defect occurred spontaneously in that individual.  Such individuals can, in turn, pass this defect to their offspring.

For more information, please contact the Fields Center