Three novel mutations in SQSTM1 identified in familial Paget's disease of bone.
Mutations in Sequestosome 1 (SQSTM1) have been shown to segregate with familial Paget's disease of bone (PDB). We examined the coding sequence of SQSTM1 in five PDB pedigrees and found three novel mutations clustered around the C-terminal ubiquitin associated domain. Disruptions of the C-terminal domain of SQSTM1 seem to be a leading cause of familial PDB.


BACKGROUND
The characteristic features of Paget's disease of bone (PDB) are caused by focal areas of excessive and uncoordinated bone remodeling. A total of seven genetic loci (PDB1-PDB7) have been reported to be associated with the disease. The gene for Sequestosome 1 (p62; SQSTM1) has been identified as the causative gene for PDB3 in numerous French-Canadian families and families predominantly of British descent. To date, a total of three mutations, all affecting the ubiquitin-associated domain of SQSTM1, have been identified: a single 1215 C to T (P392L) transversion in exon 8, a T insertion in exon 8 (E396X), and a G to A mutation at the splice junction of exon 7 (IVS7 + 1).


METHODS
DNA was isolated from blood collected from the members of five U.S. PDB pedigrees. Mutation analysis of the coding sequence of the SQSTM1 gene was performed on the proband and other key individuals in the pedigrees.


RESULTS
Four of the five families had SQSTM1 mutations. Three of these mutations were novel: a single base deletion in exon 8 at position 1210 (1210delT) resulting in a premature stop codon at amino acid 394, a single C deletion in exon 8 at position 1215 (1215delC) also resulting in a premature stop codon at amino acid 394, and a single 1200 C to T (P387L) transversion in exon 7.


CONCLUSIONS
Noteworthy is the fact that these three SQSTM1 mutations, in addition to the three previously described mutations, are clustered near the C-terminal of the protein. These mutations may be acting in a dominant-negative fashion to disrupt the ubiquitin-binding function, which could result in abnormal activation of the NF-kappaB pathway and the subsequent activation of the osteoclasts. These findings imply that SQSTM1 mutations may play a role in the majority of familial PDB in the United States.
Johnson-Pais
Teresa L
TL
Department of Pediatrics, University of Texas Health Science Center, San Antonio, Texas 78229, USA. paist@uthscsa.edu
Wisdom
Julie H
JH
Weldon
Korri S
KS
Cody
Jannine D
JD
Hansen
Marc F
MF
Singer
Frederick R
FR
Leach
Robin J
RJ
D048868:Adaptor Proteins, Signal Transducing; D017398:Alternative Splicing; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D004252:DNA Mutational Analysis; D005091:Exons; D005260:Female; D006801:Humans; D007438:Introns; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D010001:Osteitis Deformans / Q000235:genetics*; D010375:Pedigree; D017434:Protein Structure, Tertiary; D011506:Proteins; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin / Q000737:chemistry
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D016328:NF-kappa B; D011506:Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin