Exclusion mappingofchromosomal regions which crosshybridise toFSHD1A associated markers inFSHD1B

Facioscapulohumeral muscular dystrophy (FHSD)isa genetically heterogeneous, autosomal dominantprimarydisease of muscle. Thepredominant formofFSHD, whichhasbeendesignated FSHD1A,has beenlocalised tothe4q34region ofhuman chromosome 4.Thedisease locus(loci) for theremaining FSHD families, whichare notlinked tochromosome4andhavebeen designated FSHD1B,hasnotyetbeen identified. The D4F104S1markerwhichdetects copies ofa 3*2kbtandemrepeat(D4Z4) whichcontains several typesofrepetitive sequences, including Hox gene-like elements,hasbeenshowntobeclosely linked tothechromosome4FHSD disease locus. Theloss ofanintegral numberofthe3-2kb tandemrepeats hasbeenassociated with FSHD1A.When hybridised to chromosomalspreads thesesequences cross hybridise withheterochromatin onacrocentric chromosomes andspecific areasof human chromosomes1,3,and10.Potentially thesespecific regions ofcrosshybridisation maybelinked toFSHD1B.To examinethispossibility we havecarried outlinkage studies inourlargest FSHD1B family. Inthis paperweexclude these areas ofspecific crosshybridisation asdisease lociforFSHD1B. (JMedGenet1995;32:770-773)