Apert syndrome is a form of acrocephalosyndactyly, a congenital disorder characterized by malformations of the skull, face, hands and feet. It is classified as a branchial arch syndrome, affecting the first branchial (or pharyngeal) arch, the precursor of the maxilla and mandible. Disturbances in the development of the branchial arches in fetal development create lasting and widespread effects.

"Syndactyly" refers to the webbing of fingers and toes

In 1906, Eugène Apert, a French physician, described nine people sharing similar attributes and characteristics. Linguistically, “acro” is Greek for “peak”, referring to the “peaked” head that is common in the syndrome. “Cephalo”, also from Greek, is a combining form meaning “head”. “Syndactyly” refers to webbing of fingers and toes.

In embryology, the hands and feet have selective cells that die, called selective cell death or apoptosis, causing separation of the digits. In the case of acrocephalosyndactyly, selective cell death does not occur and skin, and rarely bone, between the fingers and toes fuses.

The cranial bones are affected as well, similar to Crouzon syndrome and Pfeiffer syndrome. Craniosynostosis occurs when the fetal skull and facial bones fuse too soon in utero, disrupting normal bone growth. Fusion of different sutures leads to different patterns of growth on the skull. Examples include: trigonocephaly (fusion of the metopic suture), brachycephaly (fusion of the coronal suture), dolichocephaly (fusion of the sagittal suture), plagiocephaly (fusion of coronal and lambdoidal sutures unilaterally), and oxycephaly or turricephaly (fusion of coronal and lambdoid sutures).

The largest study shows an incidence of 1 per 65000 live births, with no preference for either sex.

Signs and symptoms

Craniosynostosis

Features of craniosynostosis

The cranial malformations are the most apparent effects of acrocephalosyndactyly. Craniosynostosis occurs, with brachiocephaly being the common pattern of growth. Another common characteristic is a high, prominent forehead with a flat posterior skull. Due to the premature closing of the coronal sutures, increased cranial pressure can develop, leading to mental deficiency. A flat or concave face may develop as a result of deficient growth in the mid-facial bones, leading to a conditir prognathism. Other features of acrocephalosyndactyly may include shallow bony orbits and broadly spaced eyes. Low-set ears are also a typical characteristic of branchial arch syndromes.

Syndactyly

All acrocephalosyndactyly syndromes show some level of limb anomalies so it can be hard to tell them apart. However, the typical hand deformities in patients with Apert Syndrome distinguish it from the other syndromes. The hands in patients with Apert syndrome always show four common features:

1. a short thumb with radial deviation
2. complex syndactyly of the index, long and ring finger
3. symbrachyphalangism
4. simple syndactyly of the fourth webspace

The deformity of the space between the index finger and the thumb may be variable. Based on this first webspace, we can differentiate three different types of hand deformation:

• Type I: Also called a “spade hand”. The most common and least severe type of deformation. The thumb shows radial deviation and clinodactyly but is separated from the index finger. The index, long and ring finger are fused together in the distal interphalangeal joints and form a flat palm. During the embryonic stage the fusion has no effect on the      longitudinal growth of these fingers so they have a normal length. In the fourth webspace we always see a simple syndactyly, either complete or incomplete.
• Type II: Also called a “spoon” or “mitten” hand. This is a more serious anomaly since the thumb is fused to the index finger by simple complete or incomplete syndactyly. Only the distal phalanx of the thumb is not joined in the osseous union with the index finger and has a separate nail. Because the fusion of the digits is at the level of the distal interphalangeal joints, a concave palm is formed. Most of the time complete syndactyly of the fourth webspace.
• Type III:  Also called the “hoof” or “rosebud” hand. This is the most uncommon but also most severe form of hand deformity in Apert syndrome. There is a solid osseous or cartilaginous fusion of all digits with one long, conjoined nail. The thumb is turned inwards and often it is impossible to tell the fingers apart. Usually proper imaging of the hand is very difficult, due to overlap of bones, but physical examination alone is not enough to measure the severity of deformation.