Mutations in lipid transporter ABCA12 in harlequin ichthyosis and functional recovery by corrective gene transfer
Masashi Akiyama, … , Daisuke Sawamura, Hiroshi Shimizu
Masashi Akiyama, … , Daisuke Sawamura, Hiroshi Shimizu
Published July 1, 2005
Citation Information: J Clin Invest. 2005;115(7):1777-1784. https://doi.org/10.1172/JCI24834.
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Research Article Dermatology

Mutations in lipid transporter ABCA12 in harlequin ichthyosis and functional recovery by corrective gene transfer

Abstract

Harlequin ichthyosis (HI) is a devastating skin disorder with an unknown underlying cause. Abnormal keratinocyte lamellar granules (LGs) are a hallmark of HI skin. ABCA12 is a member of the ATP-binding cassette transporter family, and members of the ABCA subfamily are known to have closely related functions as lipid transporters. ABCA3 is involved in lipid secretion via LGs from alveolar type II cells, and missense mutations in ABCA12 have been reported to cause lamellar ichthyosis type 2, a milder form of ichthyosis. Therefore, we hypothesized that HI might be caused by mutations that lead to serious ABCA12 defects. We identify 5 distinct ABCA12 mutations, either in a compound heterozygous or homozygous state, in patients from 4 HI families. All the mutations resulted in truncation or deletion of highly conserved regions of ABCA12. Immunoelectron microscopy revealed that ABCA12 localized to LGs in normal epidermal keratinocytes. We confirmed that ABCA12 defects cause congested lipid secretion in cultured HI keratinocytes and succeeded in obtaining the recovery of LG lipid secretion after corrective gene transfer of ABCA12. We concluded that ABCA12 works as an epidermal keratinocyte lipid transporter and that defective ABCA12 results in a loss of the skin lipid barrier, leading to HI. Our findings not only allow DNA-based early prenatal diagnosis but also suggest the possibility of gene therapy for HI.

Authors

Masashi Akiyama, Yoriko Sugiyama-Nakagiri, Kaori Sakai, James R. McMillan, Maki Goto, Ken Arita, Yukiko Tsuji-Abe, Nobuko Tabata, Kentaro Matsuoka, Rikako Sasaki, Daisuke Sawamura, Hiroshi Shimizu

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Verification of splice-site mutation IVS23-2A→G and conservation of resi...
Verification of splice-site mutation IVS23-2A→G and conservation of residues deleted by mutations IVS23-2A→G and 4158_4160delTAC (T1387del). (A) RT-PCR analysis of mRNA fragments around the exon 23–24 boundary indicated that keratinocytes from patient 1 (lane P) showed 2 different mutant transcripts, 674 bp and 513 bp, which were shorter than the control transcript (683 bp) from healthy human keratinocytes (lane C). Lane M, markers. (B) Sequencing of the mutant transcripts and the control transcript revealed that 9 nucleotides and 170 nucleotides were deleted in mutant transcripts. (C) A 9-nucleotide deletion resulted in the loss of 3 amino acids from the N terminal sequence of exon 24 (Y1099_K1101del), and the 170-nucleotide deletion led to a frameshift. (D) ABCA12 amino acid sequence alignment shows the level of conservation in diverse species of the amino acids, Y1099_K1101 and T1387 (red characters), which were deleted by mutations in HI families. Asterisks indicate ABC (abt-4).