What is harlequin ichthyosis?
Harlequin ichthyosis is a severe inherited form of ichthyosis that presents at birth as hard, thickened armour-like plates of skin covering the entire body. Harlequin ichthyosis is also called harlequin-type ichthyosis, and harlequin fetus .
Note that harlequin syndrome refers to a different condition characterised by asymmetrical, progressive, and segmental sweat loss (also known as progressive isolated segmental anhidrosis), and to unilateral sweating and flushing on the chest, neck, and face.
Harlequin change is another unrelated condition describing rapidly fluctuating unilateral erythema in neonates.
Who gets harlequin ichthyosis?
Harlequin ichthyosis is rare, and both sexes are affected in equal numbers. It affects approximately one in 300,000 newborns .
There is no racial predilection known for harlequin ichthyosis. Higher incidence may be encountered in cultures where parental consanguinity is common .
What causes harlequin ichthyosis?
The inheritance of harlequin ichthyosis is autosomal recessive. It is due to mutations in the ABCA 12 (ATP-binding cassette sub-family A member 12) gene. The ABCA12 gene is believed to encode a transporter protein involved in the transport of epidermal lipids across cell membranes and is essential for normal skin development.
Some mutations in the ABCA12 gene prevent the cell from making any ABCA12 protein. Other mutations lead to the production of an abnormally small version of the protein that cannot transport lipids properly. A loss of functional ABCA12 protein disrupts the normal development of the epidermis, resulting in the hard, thick scales characteristic of harlequin ichthyosis .
What are the clinical features of harlequin ichthyosis?
- Skin changes are present at birth.
- The patient's skin is severely thickened with large, shiny plates of hyperkeratotic scale.
- Deep erythematous fissures separate the scales.
- Severe ectropion affecting the patient's eyelids leaves the conjunctivae and cornea at risk of desiccation, infection, and trauma.
- The nose may be poorly developed, with the patient exhibiting nasal hypoplasia, eroded nasal alae, and obstructed nares.
- The ears may be poorly developed, flattened, or absent.
- The retroauricular folds and the pinnae of the ears may be small or absent, and the external auditory canal may be obstructed by scale.
- The traction of the lips causes eclabium.
- The limbs are encased in thick, hyperkeratotic skin.
- Hypoplasia of digits and extra fingers and toes may occur.
- The thickened skin prevents normal sweat gland function and heat loss.
- Excessive fluid loss leads to dehydration.
- The rise in body temperature can cause heatstroke.
What are the complications of harlequin ichthyosis?
- The cutaneous abnormalities associated with harlequin ichthyosis disrupt the normal skin barrier.
- Poor immunity leads to infections which may be life-threatening.
- Thick, hyperkeratotic skin may cause contractures (muscle shortening) across joints and constriction of the limbs (including the fingers and toes) leading to swelling, necrosis, and autoamputation.
- The patient's respiration is also restricted. The rigid skin impedes chest wall expansion, leading to hypoventilation and respiratory failure.
How is harlequin ichthyosis diagnosed?
The diagnosis of harlequin ichthyosis relies on a physical examination of the patient and genetic laboratory investigations.
Genetic testing for a loss of function mutation in the ABCA12 gene is the most specific diagnostic test for harlequin ichthyosis.
- Mutations in the gene may cause impaired transport of lipids in the skin and shrunken versions of proteins responsible for skin development.
- Less severe mutations result in a collodion membrane and congenital ichthyosiform erythroderma-like presentation [4,5].
Skin biopsy shows a very thickened stratum corneum, parakeratosis, and hypergranulosis on histology.
What is the differential diagnosis for harlequin ichthyosis?
- Ichthyosis vulgaris (95% of cases of ichthyosis), caused by a mutation of the gene encoding the protein filaggrin (the FLG gene)
- Recessive X-linked ichthyosis, caused by a mutation of the enzyme steroid sulfatase (STS)
- Autosomal recessive congenital ichthyoses, lamellar, congenital ichthyosiform erythroderma, and Netherton syndrome
- Keratinopathic ichthyoses (caused by a mutation of a keratin gene).
- Sjögren–Larsson syndrome is caused by an inborn error of metabolism, resulting in the deficiency of an enzyme, fatty aldehyde dehydrogenase (FALDH), which is needed to produce normal oils and fats in the body.
- Its clinical features include ichthyosis, cerebral palsy, and intellectual impairment.
Gaucher disease is an autosomal recessive inborn error in glucosylceramidase, which may present as a collodion baby with developmental and neurological problems.
Trichothiodystrophy is characterised by photosensitivity, ichthyosis, brittle hair, developmental delay, and/or short stature.
X-linked chondrodysplasia punctata (Conradi–Hünermann–Happle syndrome)
- X-linked chondrodysplasia punctata is caused by a defect in cholesterol biosynthesis due to a mutation in the gene coding for emopamil-binding protein (EBP).
- X-linked chondrodysplasia leads to early gestational lethality in males.
- X-linked chondrodysplasia leads to cicatricial scarring, alopecia, patchy/diffuse ichthyosis that may resolve into atrophoderma and hyperpigmentation, punctate calcification in epiphyseal cartilage (the cartilage plate at the end of long bones), asymmetrical rhizomelic (proximal) limb shortening, cataracts, and deafness in females.
What is the treatment for harlequin ichthyosis?
There is no cure for harlequin ichthyosis, and treatment is centred around protecting the skin and preventing infection.
After birth, the thick plate-like outer layer of skin eventually splits and peels, leaving the vulnerable inner layers of the dermis exposed. Most harlequin infants will need one-on-one nursing care for the first several weeks of life. Antibiotic treatment may also be necessary to prevent or treat infection during this time.
Softening emollients, especially those containing urea, salicylic acid or alpha hydroxy acids, are particularly effective when applied after bathing while the skin is still moist. These products work to keep the skin moisturised and pliable while preventing the cracking and fissuring that can lead to secondary bacterial infection.
Early systemic treatment with oral retinoids (eg, acitretin or isotretinoin) has also been shown to heal skin fissures, soften or resolve plate-like scales, and improve overall survival .
What is the outcome for harlequin ichthyosis?
In the past, harlequin ichthyosis infants rarely survived beyond the first few days of life. With advancements in neonatal care, the survival rate has improved, with worldwide figures approaching 50% .
Children who survive the neonatal period usually evolve to a less severe phenotype of ichthyosis but continue to develop fish-like scales, and have retention of waxy, yellowing material in seborrhoeic areas, generalised poor hair growth and scarring alopecia. Harlequin ichthyosis survivors may continue to suffer from temperature dysregulation, have contractures of the digits, arthralgias, failure to thrive, hypothyroidism, and short stature.