title: PMP22exon 4 deletion causes ER retention of PMP22 and a gain-of-function allele in CMT1E.
abstract: To determine whether predicted fork stalling and template switching (FoSTeS) during mitosis deletes exon 4 in peripheral myelin protein 22 KD (PMP22) and causes gain-of-function mutation associated with peripheral neuropathy in a family with Charcot-Marie-Tooth disease type 1E.
  
  
  
  Two siblings previously reported to have genomic rearrangements predicted to involve exon 4 ofPMP22were evaluated clinically and by electrophysiology. Skin biopsies from the proband were studied by RT-PCR to determine the effects of the exon 4 rearrangements on exon 4 mRNA expression in myelinating Schwann cells. Transient transfection studies with wild-type and mutant PMP22 were performed in Cos7 and RT4 cells to determine the fate of the resultant mutant protein.
  
  
  
  Both affected siblings had a sensorimotor dysmyelinating neuropathy with severely slow nerve conduction velocities (<10 m/sec). RT-PCR studies of Schwann cell RNA from one of the siblings demonstrated a complete in-frame deletion ofPMP22exon 4 (PMP22Δ4). Transfection studies demonstrated that PMP22Δ4 protein is retained within the endoplasmic reticulum and not transported to the plasma membrane.
  
  
  
  Our results confirm that that FoSTeS-mediated genomic rearrangement produced a deletion of exon 4 of PMP22, resulting in expression of both PMP22 mRNA and protein lacking this sequence. In addition, we provide experimental evidence for endoplasmic reticulum retention of the mutant protein suggesting a gain-of-function mutational mechanism consistent with the observed CMT1E in this family. PMP22Δ4 is another example of a mutated myelin protein that is misfolded and contributes to the pathogenesis of the neuropathy.
authors.affiliation: Department of Neurology Neuromuscular Division University of Iowa Hospitals and Clinics Iowa City Iowa.
authors.forename: David S
authors.initials: DS
authors.lastname: Wang
authors.affiliation: Department of Neurology Neuromuscular Division University of Iowa Hospitals and Clinics Iowa City Iowa.
authors.forename: Xingyao
authors.initials: X
authors.lastname: Wu
authors.affiliation: Department of Neurology Neuromuscular Division University of Iowa Hospitals and Clinics Iowa City Iowa.
authors.forename: Yunhong
authors.initials: Y
authors.lastname: Bai
authors.affiliation: Departments of Neurology and Pediatrics Neuromuscular Division Washington University School of Medicine St. Louis Missouri.
authors.forename: Craig
authors.initials: C
authors.lastname: Zaidman
authors.affiliation: Department of Neurology Neuromuscular Division University of Iowa Hospitals and Clinics Iowa City Iowa; Department of Neurology Neurogenetics Division University of Iowa Hospitals and Clinics Iowa City Iowa.
authors.forename: Tiffany
authors.initials: T
authors.lastname: Grider
authors.affiliation: Department of Neurology Neurogenetics Division University of Iowa Hospitals and Clinics Iowa City Iowa.
authors.forename: John
authors.initials: J
authors.lastname: Kamholz
authors.affiliation: Department of Pediatrics Baylor College of Medicine Houston Texas.
authors.forename: James R
authors.initials: JR
authors.lastname: Lupski
authors.affiliation: Departments of Neurology and Pediatrics Neuromuscular Division Washington University School of Medicine St. Louis Missouri.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Connolly
authors.affiliation: Department of Neurology Neuromuscular Division University of Iowa Hospitals and Clinics Iowa City Iowa; Department of Neurology Neurogenetics Division University of Iowa Hospitals and Clinics Iowa City Iowa.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Shy