Acrocephalo-syndactyly type 1
Apert syndrome is a genetic disorder characterized by the premature fusion of certain skull bones (craniosynostosis). This early fusion prevents the skull from growing normally and affects the shape of the head and face. In addition, a varied number of fingers and toes are fused together (syndactyly). It is classified as a branchial arch syndrome and specifically affects the first branchial (or pharyngeal) arch, which is the precursor of the maxilla and mandible. Since the branchial arches are important developmental features in a growing fetus, disturbances in its development create lasting and widespread effects.
Many of the characteristic facial features of Apert syndrome result from the premature fusion of the skull bones. The head is unable to grow normally, which leads to a sunken appearance in the middle of the face, bulging and wide-set eyes, a beaked nose, and an underdeveloped upper jaw leading to crowded teeth and other dental problems. Shallow eye sockets can cause vision problems. Early fusion of the skull bones also affects the development of the brain, which can disrupt intellectual development. Cognitive abilities in people with Apert syndrome range from normal to mild or moderate intellectual disability.
Individuals with Apert syndrome have webbed or fused fingers and toes. The severity of the fusion varies; at a minimum, three digits on each hand and foot are fused together. In the most severe cases, all of the fingers and toes are fused. Less commonly, people with this condition may have extra fingers or toes (polydactyly). Additional signs and symptoms of Apert syndrome can include hearing loss, unusually heavy sweating (hyperhidrosis), oily skin with severe acne, patches of missing hair in the eyebrows, fusion of spinal bones in the neck (cervical vertebrae), and recurrent ear infections that may be associated with an opening in the roof of the mouth (a cleft palate).
The cranial malformations are the most apparent effects of acrocephalosyndactyly. Craniosynostosis occurs, in which the cranial sutures close too soon, though the child's brain is still growing and expanding. Brachycephaly is the common pattern of growth, where the coronal sutures close prematurely, preventing the skull from expanding frontward or backward, and causing the brain to expand the skull to the sides and upwards. This results in another common characteristic, a high, prominent forehead with a flat back of the 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.
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:
- a short thumb with radial deviation
- complex syndactyly of the index, long and ring finger
- 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 handdeformation:
- 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, we see 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 it is often 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.
Other signs and symptoms may include:
- Distinctive facial features (bulging and wide-set eyes
- Beaked nose
- Underdeveloped upper jaw leading to crowded teeth and other dental problems
- Shallow eye sockets which can cause vision problems)
- Hearing loss
- Hyperhidrosis (increased sweating)
- Cognitive abilities in affected individuals range from normal to mild or moderate intellectual disability.
- Partially or totally joined fingers
- Partially or totally joined toes
- Premature joining of bones in the head
- Growth disturbance in the skull
- Long-shaped head
Mutations in the FGFR2 gene cause Apert syndrome and is inherited in an autosomal dominant manner. This gene produces a protein called fibroblast growth factor receptor 2. Among its multiple functions, this protein signals immature cells to become bone cells during embryonic development. A mutation in a specific part of the FGFR2 gene alters the protein and causes prolonged signaling, which can promote the premature fusion of bones in the skull, hands, and feet.
Apert syndrome is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Almost all cases of Apert syndrome result from new mutations in the gene, and occur in people with no history of the disorder in their family. Individuals with Apert syndrome, however, can pass along the condition to the next generation.
Apert syndrome and the other conditions associated with FGFR-related craniosynostosis were clinically defined long before the molecular basis of this group of disorders was discovered. Apert syndrome can be diagnosed primarily based on the following clinical findings:
- Turribrachycephalic skull shape (cone-shaped or towering skull) which is observable clinically and can be confirmed by skull radiograph or head CT examination;
- Characteristic facial features including moderate-to-severe underdevelopment of the midface, bulging and wide-set eyes, beaked nose, underdeveloped jaw and shallow eye sockets;
- Variable hand and foot findings such as syndactyly of the fingers and toes and polydactyly.
While clinical findings are suggestive of Apert syndrome, molecular genetic testing can help to confirm the diagnosis. Fibroblast growth factor receptor type 2 (FGFR2) sequence analysis is highly sensitive for Apert syndrome. More than 98% of cases are caused by a specific mutation in the 7th exon of the gene encoding FGFR2. The remaining cases are due to another specific mutation in or near exon 9 of FGFR2.
GeneTests lists laboratories offering clinical genetic testing for this condition. Clinical genetic tests are ordered to help diagnose a person or family and to aid in decisions regarding medical care or reproductive issues. Talk to your health care provider or a genetic professional to learn more about your testing options.
Surgery is needed to prevent the closing of the coronal sutures from damaging brain development. In particular, surgeries for the LeFort III or monobloc midface distraction osteogenesis which detaches the midface or the entire upper face, respectively, from the rest of the skull, are performed in order to reposition them in the correct plane. These surgeries are performed by both plastic and oral and maxillofacial (OMS) surgeons, often in collaboration.
There is no standard treatment for the hand malformations in Apert due to the differences and severity in clinical manifestations in different patients. Every patient should therefore be individually approached and treated, aiming at an adequate balance between hand functionality and aesthetics. However, some guidelines can be given depending on the severity of the deformities. In general it is initially recommended to release the first and fourth interdigital spaces, thus releasing the border rays. This makes it possible for the child to grasp things by hand, a very important function for the child's development. Later the second and third interdigital spaces have to be released. Because there are three handtypes in Apert, all with their own deformities, they all need a different approach regarding their treatment:
Type I hand usually needs only the interdigital web space release. First web release is rarely needed but often its deepening is necessary. Thumb clynodactyly correction will be needed.
In type II hands it is recommended to release the first and fifth rays in the beginning, then the second and the third interdigital web spaces have to be freed. The clynodactyly of the thumb has to be corrected as well. The lengthening of the thumb phalanx may be needed, thus increasing the first web space. In both type I and type II, the recurrent syndactyly of the second web space will occur because of a pseudoepiphysis at the base of the index metacarpal. This should be corrected by later revisions.
Type III hands are the most challenging to treat because of their complexity. First of all, it is advised to release the first and fourth webspace, thus converting it to type I hand. The treatment of macerations and nail-bed infections should also be done in the beginning. For increasing of the first web space, lengthening of the thumb can be done. It is suggested that in severe cases an amputation of the index finger should be considered. However, before making this decision, it is important to weigh the potential improvement to be achieved against the possible psychological problems of the child later due to the aesthetics of the hand. Later, the second and/or third interdigital web space should be released.
With growing of a child and respectively the hands, secondary revisions are needed to treat the contractures and to improve the aesthetics.
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