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Dermatology
Mosaicism and Linear Lesions
Built from Dermatology, 5th Edition
What’s inside
16 sections · 182 slides
Overview
- What this section covers
- A shared vocabulary
Introduction and history
Why the skin is the best place in the body to see mosaicism
- What makes a mosaic disorder
- Postzygotic versus germline mutations
- A history of naming the pattern
- An overlooked co-discoverer
- Two routes to a mosaic pattern
- Causes of mosaicism and chimerism
- How a familial mosaic disease can occur
Patterns and pathogenesis of cutaneous mosaicism
Why mosaic skin disease looks the way it does
- Mapping the lines of Blaschko
- Lines of Blaschko across the body
- An early clinical example
- Not every mosaic pattern follows Blaschko's lines
- Happle's seven patterns of cutaneous mosaicism
- Expected pattern of cutaneous mosaicism according to its timing of onset
- Timing sets the scale of the mosaic
- Cell type also shapes the pattern
- Two patterns of mosaic pigment disease
- Five ways a mosaic mutation can meet the background genotype
- Simple segmental (type 1) mosaicism
- Superimposed (type 2) mosaicism
- Revertant mosaicism - the mutation running in reverse
- Recessive disease can also become mosaic
- Matching a streak to its generalized disease
- Mosaic skin conditions and their generalized counterparts
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Mosaic skin conditions and their generalized counterparts (continued)
- Passing a mosaic mutation to the next generation
- Working through a Blaschko-linear rash
Testing for mosaicism
Why the biopsy site matters more than the blood tube
- Skin biopsy beats a blood sample
- One gene, many different-looking diseases
Functional mosaicism in X-linked disease
How a woman's own X-chromosome shuffle can paint a rash
- Lyonization makes every woman a mosaic
- What happens if a son inherits the abnormal X
- How a boy can still be born with a "lethal" X-linked disease
- An exception: CHILD syndrome
- Which X-linked diseases do NOT follow Blaschko's lines
- Boys, girls, and NEMO mutations
- Findings in girls and boys with NEMO mutations
- Findings in girls and boys with NEMO mutations (continued)
Incontinentia pigmenti
The prototype X-linked mosaic skin disease
- Incontinentia pigmenti at a glance
- How common is it, and why the name
- A name built from two case reports
- Genetics: an X-linked dominant disease, usually lethal in boys
- Pathogenesis: a pro-apoptotic state
- How loss of NEMO triggers cell death in incontinentia pigmenti
- Four skin stages over a lifetime
- Stage 1: the blistering phase
- Incontinentia pigmenti, stage 1: streaks of blisters and redness
- Stages 2 and 3: verrucous plaques, then pigment streaks
- Incontinentia pigmenti: the four clinical stages
- Incontinentia pigmenti, early inflammatory stages with eosinophils on biopsy
- Incontinentia pigmenti, stage 3: scalloped hyperpigmented streaks
- Stage 4 and later-life findings
- Incontinentia pigmenti, stage 4: hairless, pale streaks
- Nail changes in incontinentia pigmenti
- Beyond the skin
- Additional manifestations of incontinentia pigmenti
- Pathology, look-alikes, and treatment
Goltz syndrome
Focal dermal hypoplasia: skin, bone, and Wnt signalling
- Goltz syndrome at a glance
- Genetics: another lethal-in-boys X-linked gene
- From PORCN to dermal thinning and fat herniation
- Clinical features
- Further features and how to tell it apart
- Treatment
Other X-linked dominant genodermatoses
Four more diseases only survivable in mosaic form
- Conradi-Hunermann-Happle syndrome
- Conradi-Hunermann-Happle syndrome: linear hyperpigmentation
- CHILD syndrome
- Linear skin defects with congenital anomalies (MIDAS syndrome)
- Oral-facial-digital syndrome type I
X-linked causes of Blaschko-linear pigment change
Streaky colour change as the presenting sign of a systemic disease
- Three rarer X-linked syndromes
- Two carrier states that show up as streaks
- X-linked reticulate pigmentary disorder
Epidermal nevi and related syndromes
A mosaic birthmark of the top skin layer, with many genetic causes
- What an epidermal nevus looks like
- Non-epidermolytic verrucous epidermal nevi
- Two families of epidermal nevus
- Organoid epidermal nevi: nevus sebaceus, woolly hair, and comedones
- More examples of the keratinocytic type
- An extensive epidermal nevus
- A further example of a non-epidermolytic verrucous epidermal nevus
- Splitting keratinocytic nevi further
- Epidermolytic verrucous epidermal nevus: clinical and biopsy findings
- The genes behind epidermal nevi
- Which gene, which nevus
- An FGFR3-driven nevus, and a lookalike acquired lesion
- The gene map for epidermal nevi
- Epidermal nevi: associated genes and syndromic associations
- Epidermal nevi: associated genes and syndromic associations (continued)
- Epidermal nevi: associated genes and syndromic associations (continued)
- Epidermal nevi: associated genes and syndromic associations (continued)
- Epidermal nevi: associated genes and syndromic associations (continued)
- Epidermal nevi: associated genes and syndromic associations (continued)
- Epidermal nevi: associated genes and syndromic associations (continued)
- Epidermal nevus syndromes: naming a broad idea
- Phakomatosis pigmentokeratotica and Schimmelpenning syndrome
- Cutaneous skeletal hypophosphatemia syndrome
- PIK3CA-related overgrowth spectrum (PROS)
- Managing PROS
- Proteus syndrome
- Proteus syndrome: risk and treatment
- Superimposed mosaic PTEN disease (SOLAMEN syndrome)
- SOLAMEN syndrome: epidermal nevus, vascular malformation, and fatty overgrowth
- ILVEN: inflammatory linear verrucous epidermal nevus
- Inflammatory linear verrucous epidermal nevus (ILVEN)
- Telling ILVEN apart from its look-alikes
Mosaic forms of other dominant skin diseases
When a familiar diagnosis shows up as a streak instead of a rash
- Simple segmental versus superimposed - a quick comparison
- Linear Darier disease
- Linear Darier disease: hyperpigmented, keratotic papules
- Linear Hailey-Hailey disease
- Superimposed (type 2) segmental Hailey-Hailey disease
- Linear porokeratosis
- Porokeratotic adnexal ostial nevus (PAON)
- Porokeratotic eccrine ostial and dermal duct nevus
- Linear basal cell nevus syndrome
- Curry-Jones and Happle-Tinschert syndromes
- Mosaic neurofibromatosis type 1 and Legius syndrome
- Mosaic tuberous sclerosis complex and other benign tumours
- Encephalocraniocutaneous lipomatosis (Haberland syndrome)
Vascular malformations
Birthmarks made of blood vessels, one mosaic mutation at a time
- Venous and glomuvenous malformations
- Capillary malformations and port-wine birthmarks
- Phakomatosis pigmentovascularis type II: dermal melanocytosis and port-wine birthmark
Pigmented lesions with a mosaic pattern
Congenital moles and cafe-au-lait patches, gene by gene
- Congenital melanocytic nevi (CMN)
- The genes behind CMN
- Nevus spilus (speckled lentiginous nevus)
- Nevus spilus and its two named syndromes
- McCune-Albright syndrome
Linear inflammatory skin disease
Ordinary rashes that sometimes choose to follow Blaschko's lines
- Why an inflammatory rash goes linear
- Linear psoriasis
- Linear psoriasis
- Linear psoriasis: streaks of erythematous scaly papules and plaques
- Linear lichen planus
- Linear lichen planus
- Lichen striatus
- "Blaschkitis"
- Other diseases that can go linear
- Exaggerated eczema along the lines of Blaschko
- Exaggerated eczema along the lines of Blaschko
- Linear lichenoid graft-versus-host disease
- Linear atrophoderma of Moulin
- Linear atrophoderma of Moulin: cliff-drop hyperpigmented depressions
- Linear atrophoderma of Moulin: a further example
Pigmentary mosaicism
Streaky and block-like colour change, and the syndromes it can flag
- Colour change as its own mosaic category
- What causes it
- Linear versus block-like patterns
- The single most common named cause: mosaic MTOR mutations
- RHOA-related neuroectodermal syndrome
- Blaschko-linear hypopigmentation from a mosaic RHOA mutation
- Two further named chromosomal causes
- Evaluating a child with patterned pigment change
- Nevus depigmentosus
Chimerism
When two genetically different embryos become one person
- How chimerism differs from mosaicism
- What chimerism looks like on the skin
- Key takeaways
- Key takeaways, continued
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- Dermatology, 5th Edition (2-Volume Set)