KRT2

KRT2 encodes a type II keratin required for the structural integrity of the suprabasal, superficial epidermis, where it assembles into intermediate filaments (PMID:26581228). Dominant mutations in KRT2 cause superficial epidermolytic ichthyosis with epidermolytic hyperkeratosis pathology, and a recurrent hotspot substitution at residue E487 marks a position critical for keratin function (PMID:26581228, PMID:35887135). The same disruption can arise somatically: a mosaic p.Asn186Asp mutation confined to lesional skin produces epidermolytic nevus, showing that a single dominant KRT2 allele compromises epidermal filament function in a tissue-restricted manner (PMID:33081034). Work on the related murine type II keratin Krt71 establishes the rod domain and its helix initiation motif as essential for linear intermediate filament assembly, where missense mutations generate filamentous aggregates and structural failure of the tissue (PMID:14573483, PMID:17143583). Beyond these genotype-phenotype correlations, no biochemical or structural characterization of KRT2 filament assembly is present in the available corpus.

1. 2003 Medium

   Established that the conserved alpha-helical rod domain of a type II keratin is functionally essential, by linking rod-domain mutations to a structural tissue phenotype.

   Evidence Positional cloning and sequencing of multiple independent mutant alleles in mouse (Krt2-6g/mK6irs1), genotype-phenotype correlation of wavy coat

   PMID:14573483

   Open questions at the time

   • Findings are in mouse Krt71, not human KRT2
   • No biochemical reconstitution of filament assembly defect
   • Hotspot residues defined genetically, not structurally
2. 2006 Medium

   Localized the requirement to the helix initiation motif of the 1A subdomain, showing this motif is needed for linear intermediate filament formation rather than filaments forming aberrant aggregates.

   Evidence ENU mutagenesis screen with two independent alleles at residues 143/146 and morphological analysis of inner root sheath intermediate filaments

   PMID:17143583

   Open questions at the time

   • Mouse keratin, not human KRT2
   • Aggregation mechanism inferred from morphology, not biochemistry
   • Single lab
3. 2016 Medium

   Defined human KRT2 as the gene whose dominant mutations cause superficial epidermolytic ichthyosis, establishing its role in superficial epidermal integrity.

   Evidence Clinical genetic sequencing and genotype-phenotype correlation across 26 families

   PMID:26581228

   Open questions at the time

   • No structural model of mutant filament disruption
   • Mechanism inferred from inheritance pattern, not direct assay
4. 2020 Medium

   Showed that a mosaic somatic KRT2 mutation is sufficient to cause localized epidermolytic disease, extending the dominant-disruption model to tissue-restricted, post-zygotic events.

   Evidence Molecular genetic testing of lesional skin versus blood DNA with allele frequency quantification (p.Asn186Asp at 25% in lesion)

   PMID:33081034

   Open questions at the time

   • Single case
   • No functional assay of the p.Asn186Asp variant
   • Filament-level consequence inferred from phenotype
5. 2022 Low

   Identified residue E487 as a recurrent hotspot for superficial epidermolytic ichthyosis, pinpointing a position critical to keratin 2 function and documenting variable expressivity.

   Evidence Clinical molecular genetics and aggregation of 34 reported cases sharing the p.Glu487Lys mutation

   PMID:35887135

   Open questions at the time

   • No in vitro or structural validation of the E487K mechanism
   • Source of variable expressivity unexplained
   • Case-series only

• How specific KRT2 rod-domain mutations biochemically disrupt intermediate filament assembly, and the basis for variable expressivity, remain uncharacterized.
• No in vitro filament assembly reconstitution for human KRT2
• No structural model of mutant rod-domain interactions
• Keratin partner pairing not characterized in the corpus