Autosomal Recessive Congenital Ichthyosis in American Bulldogs Is Associated With NIPAL4 (ICHTHYIN) Deficiency

Abstract

A minority of patients with nonsyndromic autosomal recessive congenital ichthyosis (ARCI) display mutations in NIPAL4 (ICH-THYIN). This protein plays a role in epidermal lipid metabolism, although the mechanism is unknown. The study describes a moderate form of ARCI in an extended pedigree of American Bulldogs that is linked to the gene encoding ichthyin. The gross phenotype was manifest as a disheveled pelage shortly after birth, generalized scaling, and adherent brown scale with erythema of the abdominal skin. Pedigree analysis indicated an autosomal recessive mode of inheritance. Ultrastructurally, the epidermis showed discontinuous lipid bilayers, unprocessed lipid within corneocytes, and abnormal lamellar bodies. Linkage analysis, performed by choosing simple sequence repeat markers and single-nucleotide polymorphisms near genes known to cause ACRI, revealed an association with NIPAL4. NIPAL4 was identified and sequenced using standard methods. No mutation was identified within the gene, but affected dogs had a SINE element 5′ upstream of exon 1 in a highly conserved region. Of 545 DNA samples from American Bulldogs, 32 dogs (17 females, 15 males) were homozygous for the polymerase chain reaction fragment. All affected dogs were homozygous, with parents heterozygous for the insertion. Immunolabeling revealed an absence of ichthyin in the epidermis. This is the first description of ARCI associated with decreased expression of NIPAL4 in nonhuman species.

A Defect in NIPAL4 Is Associated with Autosomal Recessive Congenital Ichthyosis in American Bulldogs

“…A clinical information questionnaire, a pedigree, and a signed informed consent document were obtained for each participant. The affected status of a dog with ARCI was verified by histopathological examination of skin biopsy samples by a board certified dermatopathologist (EAM) as previously described [6]. The study was approved by the Institutional Animal Care and Use Committee at the University of Pennsylvania (804197).…”

“…Genomic DNA extraction, polymerase chain reaction (PCR) amplification, and Sanger gene sequencing were performed as previously described [6]. Briefly, blood and tissue extractions were performed using the QIAamp DNA MiniKit (Qiagen, Valencia, CA) according to the manufacturer’s protocol.…”

“…A real-time PCR based discrimination genotyping method for variant and wild-type alleles was developed (Applied Biosystems, Carlsbad, CA) and performed on 800 DNA samples from ABDs and 150 DNA samples from clinically healthy dogs of other breeds using previously established protocols [6] and the unlabeled PCR primers (forward: ; reverse: ) and fluorescently labeled TaqMan ® 3′-Minor groove binder probes: VIC ® dye-labeled for wild type, and FAM ™ dye-labeled for the cytosine deletion mutant.…”

“…We had previously described a form of autosomal recessive congenital ichthyosis in American Bulldogs (ABDs), including clinical presentation (Fig 1), mode of inheritance, and the histopathological features of this disorder [6]. The most significant findings of ARCI in these dogs were (1) the absence of ichthyin in the outer layer of the epidermis of ARCI-affected ABDs and (2) the identification of an ARCI-associated molecular marker, a short interspersed element insertion polymorphism near the NIPAL4 gene.…”

Exome sequencing reveals a nebulin nonsense mutation in a dog model of nemaline myopathy

“…Whole blood samples from ABDs recruited for an unrelated study were obtained as controls (Mauldin et al 2014). DNA was isolated following the Gentra PureGene protocol (Qiagen).…”