Genodermatoses and neurocutaneous clues

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

The skin and nervous system share ectodermal and developmental signalling pathways, so pigment, vessels, connective tissue and appendages can mark disease in brain, eye, kidney, heart, bone or peripheral nerve. Begin with onset and evolution, pregnancy and birth history, development, seizures, headache, vision, hearing, pain, blood pressure symptoms, heat tolerance and family history. Construct a three-generation pedigree but remember that a negative family history can reflect a new variant, reduced expression or mosaicism. Examine the whole skin, scalp, hair, nails, teeth and oral mucosa and perform a focused neurological, musculoskeletal, growth and blood-pressure assessment.

Pattern narrows the pathway. Multiple bilateral café-au-lait macules with flexural freckling suggest NF1; a segmental cluster may be mosaic. Hypomelanotic ash-leaf or confetti lesions, facial angiofibromas and shagreen texture suggest tuberous sclerosis, particularly with infantile spasms or other seizures. A high-risk facial capillary malformation redirects to eye pressure and brain assessment. Blaschko-linear staged lesions in a girl suggest incontinentia pigmenti. Fragility, photosensitivity, generalized scale or abnormalities of sweat, teeth and hair move away from a neurocutaneous tumour syndrome toward epidermolysis bullosa, xeroderma pigmentosum, ichthyosis or ectodermal dysplasia.

Care is organised by the associated organ risk rather than by the visibility of the skin sign. Confirm diagnoses clinically and genomically when testing will clarify surveillance, reproductive advice or targeted treatment. Explain that blood may miss low-level or tissue-confined mosaic variants and that an uncertain result is not a diagnosis. Offer the child age-appropriate involvement and revisit consent as maturity develops. Coordinate specialties through one written plan, avoid duplicated imaging, and address pain, itch, school, appearance, transition and reproductive choices without reducing the person to a syndrome.

Key points

A genodermatosis may be inherited or post-zygotic mosaic; distribution along Blaschko lines or a body segment can be as informative as family history.
Neurofibromatosis type 1 evolves with age: café-au-lait macules appear early, axillary or groin freckling later, then neurofibromas, with eye, bone, blood-pressure and developmental risks.
Tuberous sclerosis clues include three or more hypomelanotic macules at least 5 mm, facial angiofibromas, shagreen patch and ungual fibromas alongside seizures and renal, cardiac or lung disease.
Use a Wood lamp to reveal subtle hypomelanotic macules, especially in light skin, but record shape, size and number rather than treating fluorescence as a diagnosis.
A capillary malformation over the forehead or upper eyelid can signal Sturge–Weber syndrome and glaucoma; early ophthalmology and neurological assessment is more urgent than cosmetic planning.
Incontinentia pigmenti usually follows Blaschko lines through vesicular, verrucous and hyperpigmented stages and can associate with retinal, dental and neurological abnormalities.
Recurrent blistering after minimal trauma suggests epidermolysis bullosa; wound care, pain, nutrition, infection prevention and avoidance of adhesive injury begin before subtype confirmation.
Congenital scaling, hair-shaft abnormality, missing or conical teeth, reduced sweating or extreme photosensitivity can reveal ichthyosis, ectodermal dysplasia or DNA-repair disease.
Choose genomic testing from a defined phenotype and discuss uncertain findings, mosaicism, familial implications and future autonomy before sampling.
A normal early scan or examination does not end surveillance because many neurocutaneous manifestations emerge at predictable ages.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Autosomal dominant tumour suppression

NF1 and TSC commonly arise from inherited or new heterozygous variants affecting tumour-suppressor pathways, with variable expression within families.

Post-zygotic mosaic variant

A variant acquired after fertilisation produces segmental or Blaschko-linear disease and may be undetectable in a standard blood sample.

Structural skin-protein disorder

Pathogenic variants in keratin, adhesion and basement-membrane proteins cause epidermolysis bullosa, ichthyosis and other barrier-fragility phenotypes.

DNA repair or ectodermal-development defect

Impaired ultraviolet-damage repair or appendage development creates extreme photosensitivity or linked abnormalities of hair, teeth, nails and sweat glands.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
RAS pathway disinhibition
Loss of neurofibromin increases RAS signalling, promoting pigmentary change and growth of peripheral-nerve, vascular and other tumours in NF1.
2
mTOR pathway activation
Loss of hamartin or tuberin releases mTOR signalling, producing hamartomas in skin, brain, kidney, heart, lung and eye in TSC.
3
Neurovascular mosaicism
A developmental variant can involve geographically related skin, leptomeningeal vessels and eye, linking a facial capillary mark with seizures and glaucoma.
4
Mechanical tissue fragility
Defective epidermal or junctional proteins cause skin layers to separate under minor shear, creating blisters, wounds, scar and secondary infection.
5
Appendage dysfunction
Altered ectodermal signalling impairs sweat glands, teeth, hair and nails, causing hyperthermia risk, feeding difficulty and recognisable physical clues.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

NF1 pigmentary sequence

Six or more café-au-lait macules of threshold size, bilateral axillary or inguinal freckling and later dermal neurofibromas form an age-dependent pattern.

NF1 high-risk featureRed flag

A painful rapidly enlarging hard plexiform-neurofibroma area, new weakness, sphincter symptom or persistent night pain raises malignant or compressive transformation risk.

Tuberous sclerosis skin set

Multiple hypomelanotic macules, central facial angiofibromas, connective-tissue shagreen plaque, forehead plaque and periungual fibromas accumulate with age.

Sturge–Weber clue

A persistent capillary malformation involving forehead or upper eyelid, especially with seizures, weakness or glaucoma, signals possible ipsilateral eye and leptomeningeal disease.

Incontinentia pigmenti sequence

Blaschko-linear vesicles in infancy evolve through warty and swirling hyperpigmented phases, sometimes leaving hypopigmentation, sparse hair, abnormal teeth and retinal disease.

Epidermolysis bullosa pattern

Blisters and erosions follow friction or minor trauma and may involve mouth, oesophagus, eyes and nails, with scarring severity suggesting subtype.

Appendage and photosensitivity clues

Sparse or fragile hair, nail dystrophy, abnormal teeth, reduced sweat, congenital scale or severe early freckling after minimal sun identifies a broader ectodermal or DNA-repair phenotype.

Red flags requiring action

New seizures, developmental regression, persistent headache or vomiting, focal neurology, sudden visual symptoms, painful or rapidly enlarging nerve tumour, hypertension, haematuria, respiratory decline, extensive blistering or infection, inability to sweat with hyperthermia, or an evolving tumour within a mosaic lesion requires urgent syndrome-specific assessment.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Phenotype map and pedigreeFirst step
Why
Define diagnostic criteria, mosaic distribution and inheritance probability before testing.
Interpretation and limitations
Count and measure lesions, map segments and Blaschko lines, photograph with consent and record relatives' skin, neurological, tumour, renal, dental and reproductive histories.
02
Wood-lamp examination
Why
Increase contrast of subtle hypomelanotic macules in suspected tuberous sclerosis or pigmentary mosaicism.
Interpretation and limitations
Use a dark room and count lesions at least 5 mm, but interpret with morphology and systemic signs because isolated hypopigmentation is common.
03
Age-specific ophthalmic assessment
Why
Detect optic-pathway dysfunction, Lisch nodules, retinal lesions or glaucoma.
Interpretation and limitations
Choose visual assessment, optic-nerve examination, retinal review and intraocular pressure by syndrome and age; new visual behaviour or pain needs urgent examination, not screening delay.
04
Neurological and developmental assessment
Why
Identify seizures, learning difference, focal deficit, hydrocephalus or intracranial tumour.
Interpretation and limitations
Use developmental and school information plus examination; EEG and brain MRI answer defined clinical or syndrome-specific questions rather than being routine for every pigmentary mark.
05
Syndrome-directed organ surveillance
Why
Find renal, cardiac, pulmonary, vascular, skeletal and endocrine complications before irreversible harm.
Interpretation and limitations
For TSC coordinate renal imaging and function, cardiac review and age-appropriate lung assessment; for NF1 check blood pressure, growth, puberty, spine and bone and investigate symptoms selectively.
06
Genomic testing
Why
Confirm a clinical diagnosis, distinguish overlapping syndromes and inform familial and reproductive care.
Interpretation and limitations
Use the current genomic test directory and genetics advice; sequence and dosage analysis may be needed, and affected-tissue testing can be more informative than blood in mosaic disease.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Isolated birthmark

One café-au-lait, hypomelanotic or capillary lesion without threshold number, high-risk site or systemic feature is commonly non-syndromic.

Legius and other RASopathy

Multiple café-au-lait macules and freckling without NF1 tumours can reflect SPRED1-related Legius syndrome or another RAS–MAPK disorder.

Pigmentary mosaicism

Blaschko-linear hypo- or hyperpigmentation with developmental or skeletal findings can represent mosaic chromosomal or single-gene disease.

Vitiligo or post-inflammatory change

Acquired depigmentation and prior inflammation can mimic hypomelanotic macules but have different distribution, texture, history and systemic associations.

Acquired blistering or scaling disorder

Infection, burns, autoimmune bullous disease, eczema and psoriasis differ by age of onset, inflammatory border, trauma relationship and biopsy findings.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01First-line phenotype routeMap skin and linked organsFirst stepFirst lineMultiple congenital, patterned or syndromic skin signs are identified.

1Record lesion type, size, count, distribution and age of appearance and examine hair, nails, teeth, eyes, blood pressure, growth, development and neurology.
2Construct a three-generation pedigree and identify the organ complication that would cause most immediate harm, arranging its specialist assessment first.
3Refer to clinical genetics or the appropriate neurocutaneous service with photographs, measurements and a focused diagnostic question rather than an unfiltered feature list.

02NF1 surveillanceFollow an age-dependent phenotypeNF1 diagnostic criteria or a confirmed pathogenic NF1 variant is present.

1At least annually assess blood pressure, skin and plexiform lesions, vision and visual behaviour, growth, puberty, spine, limbs, development, learning and school function at age-appropriate depth.
2Investigate new persistent pain, rapid hard growth, neurological deficit, sphincter change, headache or hypertension urgently with the relevant specialist and targeted imaging.
3Avoid routine whole-body or brain imaging in an asymptomatic child unless the specialist surveillance pathway identifies a specific indication.

03TSC surveillanceCoordinate brain, kidney, heart and lung careClinical criteria or genomic testing supports tuberous sclerosis complex.

1Assess seizures and development promptly, obtain syndrome-directed brain imaging and EEG when indicated and provide an emergency plan for prolonged or clustered seizures.
2Schedule renal imaging, renal function and blood pressure, cardiac review and age- and sex-appropriate pulmonary assessment through a specialist TSC service.
3Treat disfiguring or symptomatic skin lesions with specialist topical, laser or procedural options while monitoring systemic mTOR-inhibitor infection, metabolic and reproductive risks when used.

04Barrier-failure routeProtect skin before subtype confirmationMinimal trauma causes blistering, erosion or extensive congenital scale.

1Use non-adhesive handling, soft dressings, wound drainage where trained, analgesia, temperature and fluid protection and urgent culture and sepsis assessment when infection is suspected.
2Refer early to the national or regional epidermolysis-bullosa or ichthyosis service for biopsy handling, genomic confirmation, nutrition, dental, eye and airway or oesophageal review.
3Give family and nursery or school an injury-minimising care plan without blaming ordinary handling, while still assessing any separate safeguarding concern on its own evidence.

05Genomic-consent routeTest with future implications visibleA genomic result could confirm diagnosis, alter surveillance or reveal familial risk.

1Explain possible positive, negative, uncertain and incidental outcomes, the chance of mosaicism and who in the family may be affected before obtaining a sample.
2Use the phenotype-matched test and record whether parental samples or affected tissue may help interpretation; do not treat a variant of uncertain significance as causal.
3Return results with genetics support, update surveillance only when clinical and molecular evidence justify it and revisit the child's own consent and reproductive questions over time.

Key medicines and prescribing safety1 treatment · regimens, roles and cautions

Reduces scale, fissuring, itch and water loss and supports the barrier while subtype-specific care is organised.

Emollient ointment for ichthyosis or fragile skin

Apply a bland fragrance-free ointment generously and repeatedly according to skin area and specialist plan, especially after bathing; use keratolytic additives only at age-, site- and surface-area-appropriate strength.

Large-area salicylic-acid or urea products can sting or be systemically absorbed in young children and broken skin. Emollient residue increases fire intensity, and heat intolerance requires cooling rather than heavier occlusion.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Neurological and developmental disease

Seizures, hydrocephalus, tumours, focal deficits, autism, attention and learning differences can arise and require age-specific support.

Vision loss

Optic-pathway tumour, glaucoma and retinal disease can impair vision before a young child can describe symptoms.

Tumour and organ burden

Peripheral-nerve malignancy, renal angiomyolipoma, renal cancer, cardiac rhabdomyoma and pulmonary disease cause substantial syndrome-specific morbidity and mortality.

Barrier failure and infection

Blistering and keratinisation disorders cause wounds, sepsis, fluid and heat imbalance, anaemia, scarring and nutritional compromise.

Psychosocial and familial impact

Visible difference, pain, learning need, uncertain prognosis and heritable risk affect education, independence, relationships and reproductive decision-making.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Maintain one syndrome-specific surveillance table listing organ, test, interval, result and responsible clinician and update it at transition between paediatric and adult services.
In NF1 review blood pressure, vision, growth, puberty, learning, spine, bone and tumour pain at least annually and provide urgent access for a changing plexiform lesion.
In TSC track seizure control, development, renal imaging and function, cardiac findings and age-appropriate pulmonary risk, with medicine monitoring when mTOR therapy is used.
For a high-risk facial capillary malformation continue ophthalmic pressure surveillance and neurological follow-up even after a normal initial assessment.
For blistering and keratinisation disorders monitor wounds, infection, pain, nutrition, anaemia, teeth, eyes, hands, feet, airway and oesophagus according to subtype.
Revisit how visibility, pain, schooling, work, insurance questions, relationships and reproductive choices affect the person and offer psychology and peer support without assuming distress.
Revisit genomic interpretation when the phenotype evolves, without repeatedly testing in the absence of a clearer clinical question.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Age is part of diagnostic criteria

NF1 freckling and neurofibromas and TSC angiofibromas or ungual lesions emerge over time, so an incomplete young-child phenotype is expected.

Mosaic disease follows developmental maps

Segmental or Blaschko-linear findings can reflect a post-zygotic variant that is absent or present at low level in blood.

Wood lamp finds, it does not diagnose

Enhanced hypomelanotic contrast helps count lesions but must be integrated with size, shape, seizures, development and other TSC criteria.

Blood is not every tissue

A negative blood genomic result may miss a low-level mosaic variant, and affected skin can sometimes provide the decisive sample.

11Common pitfallsFrequent interpretation and management errors.

01
Calling one café-au-lait macule NF1 or one hypopigmented patch tuberous sclerosis without counts, measurements and systemic context.
02
Excluding a neurocutaneous syndrome after a normal infant examination even though diagnostic signs accumulate with age.
03
Ordering routine serial brain MRI for every asymptomatic child with NF1 instead of using age-specific clinical surveillance and targeted imaging.
04
Treating a variant of uncertain significance as proof of disease or a negative blood result as proof against mosaicism.
05
Focusing on cosmetic laser treatment for a forehead capillary malformation before eye and neurological risk assessment.
06
Using adhesive dressings or vigorous handling on suspected epidermolysis bullosa skin.
07
Missing heat illness in a child with reduced sweating, sparse hair and abnormal teeth.
08
Failing to coordinate surveillance results across specialties and losing renal, eye or tumour follow-up during transition.