A neonate is born with thick, plate-like armor of skin separated by deep red fissures over the entire body. There is severe ectropion (everted eyelids), eclabium (everted lips with a fixed open mouth), flattened nose and ears, and constrictive bands around the digits. Within the first hours of life the infant develops hypothermia, tachypnea, hypernatremia, and feeding failure from the catastrophic transepidermal fluid and electrolyte loss across the disrupted skin barrier.
AR; ABCA12 encodes an ATP-binding cassette transporter required to load glucosylceramides into lamellar granules of the stratum corneum. Functional ABCA12 is essential for the lamellar lipid layer that constitutes the epidermal water barrier.
| ABCA12 variant type | Phenotype |
|---|---|
| Biallelic loss-of-function (truncating) | Harlequin ichthyosis; most severe |
| Biallelic missense with residual function | Lamellar ichthyosis or congenital ichthyosiform erythroderma (milder autosomal recessive congenital ichthyoses) |
Carrier frequency is low; the disease is rare. Recurrence in siblings of affected probands is the classic 25%.
At birth:
- Massive plate-like hyperkeratotic scales with deep erythematous fissures forming a geometric "armor"
- Ectropion: everted lower eyelids with conjunctival exposure
- Eclabium: everted lips, fixed open mouth ("O" sign)
- Flattened, hypoplastic nose and ears
- Constrictive bands around fingers and toes (autoamputation risk)
- Digits may appear underdeveloped from in-utero compression
Acute neonatal complications (drive early mortality):
- Hypothermia (impaired thermoregulation)
- Severe hypernatremic dehydration from transepidermal water loss
- Respiratory compromise (chest restriction by armor, plus difficulty feeding/breathing through fixed-open mouth)
- Sepsis (compromised skin barrier)
- Feeding failure
- Corneal exposure injury from ectropion
If they survive infancy (significantly improved with modern NICU care):
- Transition to a severe lamellar ichthyosis phenotype with chronic erythroderma
- Persistent ectropion, scarring alopecia, joint contractures
- Heat intolerance (impaired sweating)
- Normal cognitive development is the rule when neurologic injury is avoided
- Clinical recognition at birth is unmistakable
- ABCA12 sequencing (and del/dup analysis) confirms
- Prenatal diagnosis available by molecular testing in known-carrier couples; 3D fetal ultrasound has limited sensitivity (severe cases may show fixed open mouth, fixed-flexion limb posture, ectropion late in 2nd trimester)
Neonatal, treat as a critical-care emergency:
- NICU admission with humidified incubator; meticulous fluid/electrolyte management
- Early systemic retinoid (acitretin): has substantially improved survival; initiate within first days of life
- Bland emollients (avoid keratolytics in raw skin)
- Eye lubrication; ophthalmology consult for ectropion
- Empiric antibiotics for sepsis (low threshold)
- Pain control during peeling phase
- Cardiology, ENT, plastics consults as needed; multidisciplinary skin team
Long-term:
- Lifelong retinoids (often acitretin or isotretinoin) to manage hyperkeratosis
- Aggressive emollient regimen
- Ophthalmologic care for ectropion
- Hearing assessment (canal occlusion by scale)
- Reproductive counseling for parents (25% sibling recurrence) and patient (autosomal recessive)
Historically near-uniformly fatal in the neonatal period; with early systemic retinoids and modern NICU care, survival now exceeds 50%. Survivors transition to a severe but stable lamellar ichthyosis phenotype with normal cognitive development.