Ichthyoses

Introduction

Ichthyoses are a group of disorders characterized by scaling of the skin

  • Can be inherited or acquired
  • Due to abnormalities in a wide variety of genes with a wide variety of functions
  • Result in epidermal hyperplasia and formation of excess stratum corneum accompanied by abnormal desquamation and visible accumulation of scales on skin’s surface
  • Can be non-syndromic or syndromic
  • Diagnosis is based on:
    • Skin findings
    • History
    • Histology
    • Associated symptoms
    • Genetic testing

Although there are many types of ichthyoses, this reference will discuss three:

  • Ichthyosis vulgaris
  • X-linked ichthyosis
  • Trichothiodystrophy

 

Ichthyosis vulgaris  

  • Most common type, occurring in 1 in 250 births
  • Caused by loss of function mutations in filaggrin gene (FLG)
    • Inherited in autosomal semi-dominant fashion with incomplete penetrance
  • Histology: Reduction of keratohyalin granules or absence of granular layer

vulgaris.pngLeight H et al. 2015 Sep 15. http://dx.doi.org/10.2147/CCID.S89871

 

Clinical Presentation

  • Non-syndromic
  • Improves with warm, humid weather and worsens with dry, cold weather
  • Skin may appear normal at birth, may not present until age 5
  • Fine white to gray scaling most prominent on abdomen and extensor surfaces of extremities with sparing of flexures and face
  • Distribution can help distinguish from eczema, which usually involves flexural surfaces
  • Palms and soles show increased skin markings or hyper-linearity

palmsichthy_0.pnghttps://www.dermquest.com/image-library/image/5044bfcfc97267166cd624a6?_...

 

  • May have keratosis pilaris (most prominent on upper arms and legs)

keratosispilaris_0.pnghttp://www.aocd.org/?page=KeratosisPilaris

Associations

  • Increased risk for asthma, allergies, atopic dermatitis

 

X-linked ichthyosis

  • Second most common type, occurring in 1 in 6000 male births
  • Caused by mutation in STS gene on Xp22.3
    • Encodes steroid sulfatase
    • Most commonly a complete gene deletion

 

Clinical Presentation:

  • Non-syndromic
  • Generalized peeling in neonatal period and fine scaling on the trunk and extremities in infancy 

xlinkedichthy.png     http://www.dermis.net/dermisroot/en/40080/image.htm

 

  • Scales become more hyperpigmented over time
  • Axillae and lateral neck often involved, popliteal and antecubital fossa and central face are spaced
  • Often clinically indistinguishable from ichthyoses vulgaris

Associations

  • Asymptomatic corneal opacities in Descemet’s membrane in 50% of patients
  • Increased risk of cryptorchidism
  • Increased risk of testicular cancer unrelated to testicular maldescent 

Prenatal Diagnosis

  • Can be made with maternal serum markers
  • Decreased placental sulfatase activity is associated with low estriol levels
    • May lead to poor initiation and progression of labor

 

Trichothiodystrophy

  • Heterogeneous group of disorders characterized by sulfur-deficient brittle hair with hair-shaft abnormalities
    • (e.g. trichoschisis, trichorrhexis nodosa, ribboning)
  • Most patients have mutation in ERCC2/XPD gene on chromosome 19q13.2-q13.3
    • Encodes the basal transcription/DNA repair factor IIH

Clinical Presentation:

  • Syndromic
    • Photosensitivity
    • Ichthyosis
    • Intellectual impairment
    • Short stature
    • Cataracts
    • Dystrophic nails 

 babytryichthy.png          http://www.ijpd.in/text.asp?2014/15/3/127/143669

 

nailsichthy_0.pngKralund H et al (2013) Xeroderma Pigmentosum-Trichothiodystrophy overlap patient with novel XPD/ERCC2mutation Rare Diseases. Ann Dermatol Venereol 134(3 Pt 1) :245-248

Microscopic examination

  • Microscopic examination of the hair reveals transverse fractures of hair
    • Examination of the hair shaft under polarized light demonstrates alternating light and dark bands
    • resembles a “tiger tail” pattern

Treatment

  • Emollients, humectants, and/or keratolytics are usually sufficient
  • Management of bacterial skin infections, commonly staphylococcal or streptococcal, is done with topical mupirocin or bacitracin

 

Recent Research

  • Mutations in TTDN1 gene have been shown to cause a non-photosensitive type of trichothiodystrophy
  • Researchers are attempting to use genetic pharmacology to increase the body’s own production of normal filaggrin

 

 References

  1. Fernandes NF, Janniger CK, Schwartz RA. X-linked ichthyosis: an oculocutaneous genodermatosis. J Am Acad Dermatol 2010; 62:480.
  2. Gonzales-Carait PN, Nicolas MO. Brittle hair and ichthyosis in the newborn: A case of Tay syndrome. Indian J Paediatr Dermatol [serial online] 2014; 15:127-9.
  3. Hashimoto S, Egly JM. Trichothiodystrophy view from the molecular basis of DNA repair/transcription factor TFIIH. Hum Mol Genet 2009; 18:R224.
  4. Leight H, Zinn Z, Jalali O. Bilateral lower extremity hyperkeratotic plaques: a case report of ichthyosis vulgaris. Clin Cosmet Investig Dermatol 2015 Sep 15; 8: 485-8. doi: http://dx.doi.org/10.2147/CCID.S89871
  5. Oji V, Tadini G, Akiyama M, et al. Revised nomenclature and classification of inherited ichthyoses: results of the First Ichthyosis Consensus Conference in Sorèze 2009. J Am Acad Dermatol 2010; 63:607.
  6. Pode-Shakked B, Marek-Yagel D, Greenberger S, et al. A novel mutation in the C7orf11 gene causes nonphotosensitive trichothiodystrophy in a multiplex highly consanguineous kindred.
  7. Eur J Med Genet. 2015 Oct 27. pii: S1769-7212(15)30036-7. doi: 10.1016/j.ejmg.2015.10.012.
  8. Smith FJ, Irvine AD, Terron-Kwiatkowski A, et al. Loss-of-function mutations in the gene encoding filaggrin cause ichthyosis vulgaris. Nat Genet 2006; 38:337.
  9. UpToDate.com: Overview of the inherited ichthyoses 

 

Back to Table of Contents