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At a glance

A type of ectodermal dysplasia characterized by hypertrichosis, atrophic skin, ectropion, and macrostomia.

Synonym

Say-Barber-Biesecker-Young-Simpson Syndrome; SBBS.

Incidence

At least 16 cases have been reported since 1982.

Genetic inheritance

Autosomal dominant inheritance caused by TWIST2-mutations on chromosome 2q37.3. However, most cases appear to be sporadic. TWIST2 encodes a transcription factor involved in the regulation of mesenchymal tissue development, mainly affecting the skin and its adnexa. Lysine instead of glutamate at TWIST2 residue 75 results in Ablepharon-Macrostomia Syndrome (AMS), whereas glutamine or alanine in the same location leads to Barber-Say Syndrome. Females seem more commonly affected than males.

Diagnosis

Based on the clinical features. Characteristic signs of BSS that distinguish it from AMS include bilateral ectropion and generalized hypertrichosis already present at birth. Skin biopsy can be helpful in the diagnosis.

Clinical aspects

This ectodermal dysplasia is characterized by marked hypertrichosis (mainly on forehead, neck, and back), an unusual face with bilateral ectropion (or less commonly microblepharon), absent or sparse eyebrows, hypertelorism, or telecanthus. The width of the nose is broad and the tip is bulbous. Macrostomia is a constant finding, often combined with thin vermillion of the lips, a high-arched and narrow palate, broad alveolar ridges with gingival fibromatosis (due to a lack of elastic fibers and an abundance of collagen fibers), and micro- and/or retrognathia. Cleft palate or high-arched palate, hearing loss and retinal changes have been described in isolated cases. Except for taurodontism in one patient, dentition is usually normal, but delayed tooth eruption and malocclusion are common. Abnormal sleep pattern and obstructive sleep apnea have been reported. The ears often have abnormally shaped conchae (microtia), are low set, and have a hypoplastic or atretic external auditory meatus. Audiometry and auditory brainstem reflexes are usually normal, although mild hearing loss has been reported. The chest is large with widely spaced, hypoplastic, inverted, or even absent nipples and the mammary glands may be hypo- or aplastic. Genital anomalies may include hypoplastic labia majora and/or minora or micropenis, hypospadias, cryptorchidism, and shawl scrotum, but are usually less severe than in AMS. Approximately one-third of male BSS patients have ambiguous genitalia. The skin is commonly thin, wrinkled, atrophic and translucent with abnormal laxity secondary to redundant skin folds. Skin histology reveals atrophic epidermis with slight orthohyperkeratosis, thin, reticular dermis, severely decreased number of elastic fibers and hypocollagenosis. Talipes equinovarus has been described in isolated cases. Mental retardation, if present is mild, however, most patients are mentally normal. Abdominal, renal, and cardiac ultrasound examinations are typically normal as are hematologic, endocrinologic, and radiologic examinations. BBS and AMS have many similarities with overlapping features. However, hypertrichosis and ectropion are typical for BSS, while micro- or ablepharon and sparse, thin hair and total absence of lanugo are more ...

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