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Pathomechanisms of Harlequin Ichthyosis and ABCA Transporters in Human Diseases

Masashi Akiyama, MD, PhD
Arch Dermatol. 2006;142(7):914-918. doi:10.1001/archderm.142.7.914.
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Objectives  To review recent advances in our understanding of the genetic pathomechanisms of harlequin ichthyosis (HI) (the most devastating subtype of congenital ichthyoses) and its prenatal diagnosis and to discuss the possibility of future gene therapy.

Data Source  PubMed search for articles about HI, its causative protein adenosine triphosphate–binding cassette A12 (ABCA12), and related molecules.

Study Selection  English-language studies were selected if they provided useful information about the pathomechanisms of HI and ABCA lipid transporters.

Data Synthesis  This article describes ABCA12 as a causative molecule involved in defects in HI, summarizes the known genetic disorders caused by genetic defects in ABCA lipid transporters, and highlights the prospects of prenatal diagnosis and gene therapy for HI.

Conclusions  Harlequin ichthyosis is caused by a serious functional deficiency of ABCA12. ABCA12 and ABCA3 are essential lipid transporters for human adaptation to a dry terrestrial environment. In clinical practice, information regarding the genetic defects and pathomechanisms underlying HI is important for precise diagnosis, genetic counseling, and prenatal diagnosis.

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Figure 1.

Newborn with harlequin ichthyosis harboring adenosine triphosphate–binding cassette A12 (ABCA12) mutations. A and C, Thick scales and fissures are seen over the entire body. B, Ectropion and eclabium are severe.

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Figure 2.

Pathogenesis of harlequin ichthyosis (HI) caused by an adenosine triphosphate–binding cassette A12 (ABCA12) deficiency. A, Model of formation of the normal intercellular lipid layers and cornified cell envelope in the stratum corneum. Formation of intercellular lipid layers in the stratum corneum is essential for correct epidermal barrier function. ABCA12 works in lipid transport via lamellar granules (LGs) to form an intercellular lipid coat. B, Model of malformation of the stratum corneum barrier in HI. Loss-of-function mutations in ABCA12 lead to defective lipid transport via LGs and malformation of intercellular lipid layers, resulting in loss of epidermal barrier function and abnormal hyperkeratosis.

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