Genomic rearrangements at the IGHMBP2 gene locus in two patients with SMARD1.
Autosomal recessive spinal muscular atrophy with respiratory distress type 1 (SMARD1) is caused by mutations in the immunoglobulin mu-binding protein 2 (IGHMBP2) gene. Patients affected by the infantile form of SMARD1 present with early onset respiratory distress. So far, patients with neither juvenile onset nor with larger deletions/rearrangements in IGHMBP2 have been reported. In this study, we investigated one patient with infantile (4 months) and another with juvenile (4.3 years) onset of respiratory distress. Direct sequencing of all exons and flanking intron sequences in both patients revealed a mutation on only one allele. In both patients, we identified genomic rearrangements of the other allele of IGHMBP2 by means of Southern blotting. Putative breakpoints were confirmed by polymerase chain reaction on genomic and cDNA. The patient with juvenile onset had an Alu/Alu mediated rearrangement, which resulted in the loss of aproximately 18.5 kb genomic DNA. At the mRNA level, this caused an in-frame deletion of exons 3-7. The patient with infantile onset had a complex rearrangement with two deletions and an inversion between intron 10 and 14. This rearrangement led to a frameshift at the mRNA level. Our results show that SMARD1 can be caused by genomic rearrangements at the IGHMBP2 gene locus. This may be missed by mere sequence analysis. Additionally, we demonstrate that juvenile onset SMARD1 may also be caused by mutations of IGHMBP2. The complex nature of the genomic rearrangement in the patient with infantile SMARD1 is discussed and a deletion mechanism is proposed.
Department of Neuropediatrics, Charité University Medical School of Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.
Ulf P
UP
Guenther
Markus
M
Schuelke
Enrico
E
Bertini
Adele
A
D'Amico
Nathalie
N
Goemans
Katja
K
Grohmann
Christoph
C
Hübner
Raymonda
R
Varon
D001483:Base Sequence; D001530:Belgium; D015139:Blotting, Southern; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics*; D040461:Gene Components; D015321:Gene Rearrangement / Q000235:genetics*; D006801:Humans; D007223:Infant; D007558:Italy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014897:Spinal Muscular Atrophies of Childhood / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
D017931:DNA Primers; D004268:DNA-Binding Proteins; C489892:IGHMBP2 protein, human; D014157:Transcription Factors