By Amara Osei

A Letter to the Editor in the August 2026 Journal of Dermatological Science ties a regulatory deletion to loss of skin-expressed steroid sulfatase isoforms. The single-family case reframes how clinicians should read one inherited keratinization disorder.

The letter appears in Volume 123, Issue 2, pages 99–101 (DOI: 10.1016/j.jdermsci.2026.05.001). Authors are Ivo F. Nagtzaam, Laurie C.M. Kouwenberg, Marieke F. van Dooren, Nicole Y.P. Souren, Antoni Gostyński, Peter M. Steijlen, and Michel van Geel. The work received no external funding, and the authors declared no competing interests.

What does the letter document?

The case centers on one patient and his family members. The authors write in their acknowledgments: "We would like to thank the patient and his family members for their contribution and cooperation in this study."

The deletion sits upstream of STS, not within its coding sequence. It eliminates expression of the skin-expressed isoforms. The framing fits an alternative-first-exon architecture for STS, as Dalla Valle and colleagues described in 2007. In that model, different first exons drive tissue-specific transcripts in skin and elsewhere.

Why does the deletion's location matter?

Elias and colleagues reviewed cholesterol sulfate's role in epidermal structure and function in 2014, a mechanism central to X-linked ichthyosis. Regulatory deletions are mechanistically distinct from coding-region losses.

Earlier prenatal work by Langlois and colleagues (2009) framed STS deficiency inside contiguous gene deletion syndrome. Brcic and colleagues (2020) mapped a wider medical and neurobehavioral phenotype in UK Biobank carriers of X-linked ichthyosis-associated genetic deletions. Together, the references situate the new case within an emerging picture of X-linked ichthyosis as a continuum rather than a single-gene disorder.

A regulatory deletion can produce the same clinical phenotype as a coding mutation, yet escape routine sequencing panels that focus on exons and splice sites. That diagnostic blind spot matters most for atypical presentations. If a regulatory deletion can selectively silence skin-expressed isoforms, dermatologists must reconsider the genotype–phenotype map. Patients whose STS coding sequencing returns normal may still carry pathogenic regulatory lesions.

What are the caveats?

• The format is a Letter to the Editor, peer-reviewed but briefer than a full original article.
• The cohort comprises one patient and his family members, sufficient for hypothesis generation but inadequate for prevalence estimates.
• The public preview shows only metadata, the CRediT authorship statement, funding declaration, and partial references; the full text is gated. Only four references appear in the public view, though the article lists eight in total.
• No external funding supported the work, a constraint the authors disclose.

What is the broader context?

The project sits within the European Reference Network-SKIN thematic group on Ichthyosis and Palmoplantar Keratoderma, a rare-disease consortium that connects specialist clinicians across Europe. Such networks routinely operate through n-of-1 and family studies because large cohorts are impractical for rare keratinization disorders. Case registries aggregate these small reports over years to build phenotypic knowledge.

A caveat follows every promise. The letter sharpens a model, but does not prove that regulatory deletions recur across unselected X-linked ichthyosis cases. Independent pedigree replication will determine whether the upstream lesion is recurrent or a one-off finding.

If replication succeeds, dermatologists may add regulatory-region analysis to the diagnostic work-up for X-linked ichthyosis. Until then, the letter functions as a pointer rather than a protocol change.