Identification of Pathogenic Variants in CYP4F22, FLG, ALOX12B, and NIPAL4 in a Case Series of Inherited Ichthyosis

Inherited ichthyoses are clinically and genetically heterogeneous disorders of cornification caused by disruption of epidermal barrier genes involved in keratinization and lipid homeostasis. Pathogenic variants in more than 50 genes have been implicated in nonsyndromic ichthyosis vulgaris (IV) and autosomal recessive congenital ichthyosis (ARCI). Here, we investigated the genetic basis of ichthyosis in four consanguineous Pakistani families presenting with IV or ARCI phenotypes. Exome sequencing followed by segregation analysis identified pathogenic variants in four established ichthyosis-associated genes: CYP4F22, FLG, ALOX12B, and NIPAL4. Identified variants include one novel nonsense allele of CYP4F22 (c.296G>A; p.Trp99*) and three known variants previously not reported in the Pakistani population. These known variants include a nonsense change in FLG, a frameshift allele of ALOX12B, and a missense variant in NIPAL4. Standardized phenotypic annotation using Human Phenotype Ontology terms revealed overlapping but variable clinical features across families, consistent with known genotype-phenotype heterogeneity in inherited ichthyosis. In silico protein modeling using AlphaFold2 and Ramachandran plot analysis predicted structural perturbations associated with the identified variants, supporting their pathogenic relevance. Publicly available scRNAseq datasets revealed greater heterogeneity of keratinocyte-associated expression patterns of these ichthyosis-associated genes in aging samples. Collectively, our findings expand the allelic and phenotypic spectrum of inherited ichthyosis in the Pakistani population and highlight the utility of comprehensive genetic analysis in consanguineous families for accurate molecular diagnosis, genetic counseling, and disease epidemiology.