Partial Loss of Function ABCA12 Mutations Generate Reduced Deposition of Glucosyl-Ceramide, Leading to Patchy Ichthyosis and Erythrodermia Resembling Erythrokeratodermia Variabilis et Progressiva (EKVP)

Clinical and genetic insights into ABCA12 variants in three Chinese families with ichthyosis: Genotype-phenotype correlation

Autosomal recessive congenital ichthyosis (ARCI) comprises a series of non-syndromic ichthyoses. Pathogenic variants in several genes associated with ARCI have so far been identified. Notably, the variants in ABCA12 play a pivotal role in the pathology of ARCI. In this study, we report three Chinese families with compound heterozygous variants in the ABCA12 gene, including two novel variants and four reported variants. Clinical and genetic analyses were conducted to explore the genotype-phenotype correlation among the patients. Immunohistochemistry and transcriptome sequencing were utilized to assess the impact of pathogenic ABCA12 variants on skin homeostasis, revealing decreased levels of ABCA12 and claudin-1, alongside increased levels of involucrin and S100A8. In conclusion, our findings contribute to updating the genotype-phenotypic correlation and provide additional evidence for the long-term use of retinoic acid drugs in patients with causative ABCA12 variants.

Protean cutaneous manifestation caused by ABCA12 variants: erythrokeratodermia variabilis-like ichthyosis and unique palmoplantar keratoderma

ABCA12 is crucial for skin barrier function and is traditionally linked to severe congenital ichthyoses, such as harlequin ichthyosis. However, its genotype-phenotype relationship may be more nuanced. Using whole-exome sequencing and Sanger sequencing, we identified four cases of mild ichthyosis with biallelic ABCA12 pathogenic variants. In addition to a milder phenotype, the palmoplantar keratoderma (PPK) in these cases had a distinct 'mosaic tile-like' pattern. Two cases with missense variants in the N-terminus of ABCA12 also presented an annular ichthyosis pattern resembling erythrokeratodermia variabilis et progressiva. Our findings suggest a correlation between ABCA12 missense variant location and clinical presentation, expanding the phenotypic spectrum associated with ABCA12 variants and highlighting the potential for annular patterns or 'mosaic tile-like' PPK in these patients.

Updated mutational spectrum and genotype-phenotype correlations in ichthyosis patients with ABCA12 pathogenic variants

Autosomal recessive congenital ichthyoses (ARCI) is a genetically heterogeneous condition that can be caused by pathogenic variants in at least 12 genes, including ABCA12. ARCI mainly consists of congenital ichthyosiform erythroderma (CIE), lamellar ichthyosis (LI) and harlequin ichthyosis (HI). The objective was to determine previously unreported pathogenic variants in ABCA12 and to update genotype-phenotype correlations for patients with pathogenic ABCA12 variants. Pathogenic variants in ABCA12 were detected using Sanger sequencing or a combination of Sanger sequencing and whole-exome sequencing. To verify the pathogenicity of a previously unreported large deletion and intron variant, cDNA analysis was performed using total RNA extracted from hair roots. Genetic analyses were performed on the patients with CIE, LI, HI and non-congenital ichthyosis with unusual phenotypes (NIUP), and 11 previously unreported ABCA12 variants were identified. Sequencing of cDNA confirmed the aberrant splicing of the variant ABCA12 in the patients with the previously unreported large deletion and intron variant. Our findings expand the phenotype spectrum of ichthyosis patients with ABCA12 pathogenic variants. The present missense variants in ABCA12 are considered to be heterogenous in pathogenicity, and they lead to varying disease severities in patients with ARCI and non-congenital ichthyosis with unusual phenotypes (NIUP).

Erythrokeratodermia Variabilis-like Phenotype in Patients Carrying ABCA12 Mutations

Erythrokeratodermia variabilis (EKV) is a rare genodermatosis characterized by well-demarcated erythematous patches and hyperkeratotic plaques. EKV is most often transmitted in an autosomal dominant manner. Until recently, only mutations in connexins such as GJB3 (connexin 31), GJB4 (connexin 30.3), and occasionally GJA1 (connexin 43) were known to cause EKV. In recent years, mutations in other genes have been described as rare causes of EKV, including the genes KDSR, KRT83, and TRPM4. Features of the EKV phenotype can also appear with other genodermatoses: for example, in Netherton syndrome, which hampers correct diagnosis. However, in autosomal recessive congenital ichthyosis (ARCI), an EKV phenotype has rarely been described. Here, we report on seven patients who clinically show a clear EKV phenotype, but in whom molecular genetic analysis revealed biallelic mutations in ABCA12, which is why the patients are classified in the ARCI group. Our study indicates that ARCI should be considered as a differential diagnosis in EKV.