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Presentation

Clinical Clues for Diagnosing Epidermal Differentiation Disorders (Ichthyosis)

Description

The talk explains how recognizing clinical clues is essential for diagnosing epidermal differentiation disorders (EDD), formerly called ichthyosis, because the exact subtype affects prognosis, screening for associated anomalies, genetic counseling, long-term management, and access to future targeted therapies. Most patients present with scaling, skin thickening, and sometimes erythema, but the pattern, severity, onset, and associated findings help narrow the diagnosis. Examples include X-linked ichthyosis with large dark polygonal scales, filaggrin-related ichthyosis vulgaris with fine scales and atopy, and keratinopathic ichthyosis with erythroderma and blistering or erosions. The speaker emphasizes that diagnosis often requires molecular testing, especially next-generation sequencing, but variants of uncertain significance may need additional functional studies such as skin biopsy, enzymatic assays, lipid studies, or engineered keratinocyte models. Deep clinical phenotyping remains crucial, focusing on birth presentation, scale morphology, skin thickening, ectropion, alopecia and hair-shaft abnormalities, palmoplantar keratoderma, disease severity, associated systemic anomalies, evolution over time, and pathognomonic patterns such as temperature-sensitive disease, Blaschko-linear mosaicism, or confetti-like revertant mosaicism.

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Conclusions

Clinical pattern recognition is essential for narrowing the diagnosis of epidermal differentiation disorders, because many genodermatoses share overlapping scaling and erythema.
The most informative clues come from a combination of findings, especially skin appearance at birth, scale morphology, skin thickening, palmoplantar keratoderma, alopecia, ectropion, associated anomalies, severity, and disease evolution.
Some neonatal presentations are highly suggestive of specific genes or subtypes, such as harlequin ichthyosis, vernix caseosa-like presentations, and erythroderma with blisters or erosions.
Disease severity can help distinguish subtypes, with milder disease often seen in FLG-related ichthyosis, intermediate severity in ALOX-related disease, and more severe disease in TGM1 or ABCA12-related forms.
Alopecia is a useful clue in selected forms and may correlate with disease severity, particularly in KRT1/KRT10, ABCA12, and TGM1-related disease.
Ectropion and palmoplantar keratoderma are supportive findings but are usually not specific enough on their own to identify a single subtype.
Associated extracutaneous abnormalities are crucial for recognizing syndromic ichthyosis and guiding broader evaluation and management.
Genetic testing, especially next-generation sequencing, is central to diagnosis, but variants of uncertain significance often require additional functional studies and deep clinical phenotyping.
Some cases can be diagnosed more confidently by recognizing distinctive evolution patterns, such as temperature-sensitive disease, mosaic Blaschko-linear lesions, or revertant confetti-like changes.
Overall, the presentation concludes that accurate classification of ichthyosis/EDD requires integration of molecular results with detailed clinical phenotyping rather than reliance on genetics alone.

Pell N et al. JID Innovation 2025.