Pfeiffer 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. Pfeiffer syndrome also affects bones in the hands and feet.

Many of the characteristic facial features of Pfeiffer syndrome result from premature fusion of the skull bones. Abnormal growth of these bones leads to bulging and wide-set eyes, a high forehead, an underdeveloped upper jaw, and a beaked nose. More than half of all children with Pfeiffer syndrome have hearing loss; dental problems are also common.

In people with Pfeiffer syndrome, the thumbs and first (big) toes are wide and bend away from the other digits. Unusually short fingers and toes (brachydactyly) are also common, and there may be some webbing or fusion between the digits (syndactyly).

Pfeiffer syndrome is divided into three subtypes. Type 1, also known as classic Pfeiffer syndrome, has symptoms as described above. Most individuals with type 1 Pfeiffer syndrome have normal intelligence and a normal life span. Types 2 and 3 are more severe forms of Pfeiffer syndrome that often involve problems with the nervous system. The premature fusion of skull bones can limit brain growth, leading to delayed development and other neurological problems. In addition, individuals with type 2 or 3 can have fusion of the bones (ankylosis) in the elbow or other joints, limiting mobility, and abnormalities of the face and airways, which can cause life-threatening breathing problems. Type 2 is distinguished from type 3 by the presence of a cloverleaf-shaped head, which is caused by more extensive fusion of bones in the skull.

Pfeiffer syndrome affects about 1 in 100,000 individuals.

Pfeiffer syndrome is most commonly caused by mutations in the FGFR2 gene. Mutations in the FGFR1 gene cause a small percentage of cases of type 1 Pfeiffer syndrome. Mutations in this gene have not been associated with type 2 or 3.

The FGFR1 and FGFR2 genes provide instructions for making proteins known as fibroblast growth factor receptors 1 and 2, respectively. Among their multiple functions, these proteins signal immature cells to become bone cells during embryonic development. A mutation in either the FGFR1 or FGFR2 gene alters the function of the respective protein, causing prolonged signaling, which can promote the premature fusion of skull bones and affect the development of bones in the hands and feet.

Normal Function

The FGFR1 gene provides instructions for making a protein called fibroblast growth factor receptor 1. This protein is one of four fibroblast growth factor receptors, which are related proteins that are involved in processes such as cell division, regulation of cell growth and maturation, formation of blood vessels, wound healing, and embryonic development.

The FGFR1 protein spans the cell membrane, so that one end of the protein is inside the cell and the other end projects from the outer surface of the cell. This positioning allows the FGFR1 protein to interact with other proteins called fibroblast growth factors (FGFs) outside the cell and to receive signals that help the cell respond to its environment. When an FGF attaches to the FGFR1 protein, the receptor triggers a cascade of chemical reactions inside the cell that instruct the cell to undergo certain changes, such as maturing to take on specialized functions. This signaling is thought to play an important role in the development and growth of several parts of the body, including the brain, bones of the head and face (craniofacial bones), bones in the hands and feet, and the long bones in the arms and legs.

Signaling through the FGFR1 protein plays a critical role in the formation, survival, and movement (migration) of nerve cells (neurons) in several areas of in the brain. In particular, this signaling appears to be essential for neurons that produce a hormone called gonadotropin-releasing hormone (GnRH). GnRH controls the production of several other hormones that direct sexual development before birth and during puberty. These hormones are important for the normal function of the ovaries in women and the testes in men. FGFR1 also appears to play a role in a group of nerve cells that are specialized to process smells (olfactory neurons). These neurons migrate from the developing nose to a structure at the front of the brain called the olfactory bulb, which is critical for the perception of odors.

Health Conditions Related to Genetic Changes

8p11 myeloproliferative syndrome

The FGFR1 gene is involved in a type of blood cancer called 8p11 myeloproliferative syndrome. This condition is characterized by an increased number of white blood cells (myeloproliferative disorder) and the development of lymphoma, a blood-related cancer that causes tumor formation in the lymph nodes. The myeloproliferative disorder usually develops into another form of blood cancer called acute myeloid leukemia. 8p11 myeloproliferative syndrome results from a rearrangement (translocation) of genetic material between chromosome 8 and another chromosome, which fuses part of the FGFR1 gene with part of another gene from the other chromosome. The most common partner gene is ZMYM2 on chromosome 13. These translocations are found only in cancer cells.

Regardless of the partner gene, the protein produced from the fused gene turns on FGFR1 signaling without the need for stimulation from growth factors. The uncontrolled signaling promotes continuous cell growth and division, leading to cancer.

Encephalocraniocutaneous lipomatosis

At least two mutations in the FGFR1 gene have been identified in people with encephalocraniocutaneous lipomatosis (ECCL), a rare condition characterized by the growth of noncancerous tumors and other abnormalities affecting the brain, eyes, and skin. The mutations that cause ECCL are not inherited from a parent; they arise randomly in one cell during the early stages of development before birth. As cells continue to grow and divide, some cells will have the mutation and other cells will not. This mixture of cells with and without a genetic mutation is known as mosaicism.

The FGFR1 gene mutations associated with ECCL change single protein building blocks (amino acids) in the FGFR1 protein. These mutations are described as "gain-of-function" because they overactivate the receptor, triggering abnormal signaling that affects cell growth and division. Researchers are studying how these changes in signaling lead to tumor growth and the other features of ECCL.

Hartsfield syndrome

At least seven mutations in the FGFR1 gene have been identified in people with Hartsfield syndrome, a rare condition characterized by holoprosencephaly, which is an abnormality of brain development, and a malformation of the hands and feet called ectrodactyly.

Some of these mutations affect one of the two copies of the FGFR1 gene in each cell, causing the autosomal dominant form of the disorder. Researchers believe that these mutations have a "dominant negative" effect, which means that the version of the FGFR1 protein produced from the mutated copy of the gene interferes with the activity of the version of the protein made from the normal copy of the gene. In other cases, mutations occur in both copies of the FGFR1 gene, causing the autosomal recessive form of the disorder.

All of the mutations associated with Hartsfield syndrome greatly reduce or eliminate the function of the FGFR1 protein, including its ability to bind to FGFs. As a result, the receptor is unable to transmit signals properly, which impairs many aspects of normal development. It is unclear how these changes lead specifically to holoprosencephaly and ectrodactyly, the characteristic features of Hartsfield syndrome.

Kallmann syndrome

Researchers have identified more than 140 FGFR1 gene mutations that can cause Kallmann syndrome, a disorder characterized by the combination of hypogonadotropic hypogonadism (a condition affecting the production of hormones that direct sexual development) and an impaired sense of smell. This condition can also affect other body systems, and its features vary among affected individuals. Researchers estimate that mutations in the FGFR1 gene account for about 10 percent of all cases of Kallmann syndrome.

The FGFR1 gene mutations that cause Kallmann syndrome change single amino acids in the FGFR1 protein or result in the production of an abnormally small, nonfunctional version of the protein. Because these mutations reduce or eliminate the function of FGFR1, preventing it from transmitting signals properly, they are described as "loss-of-function" mutations. Studies suggest that a shortage of functional FGFR1 disrupts the migration and survival of olfactory neurons and GnRH-producing neurons in the developing brain. If olfactory nerve cells do not extend to the olfactory bulb, a person's sense of smell will be impaired or absent. Misplacement or premature loss of GnRH-producing neurons prevents the production of sex hormones, which interferes with normal sexual development and causes puberty to be delayed or absent.

Some people with Kallmann syndrome resulting from FGFR1 gene mutations have additional features, such as a split in the lip (cleft lip) with an opening in the roof of the mouth (a cleft palate), abnormal tooth development, and abnormalities of the hands and feet. It is unclear how mutations in the FGFR1 gene lead to these other signs and symptoms. Because these features vary among individuals, researchers suspect that other genetic and environmental factors may be involved. Some affected individuals have mutations in one of several other genes in addition to FGFR1, and these genetic changes may contribute to the varied features of the condition.

Osteoglophonic dysplasia

At least three mutations in the FGFR1 gene can cause a rare condition called osteoglophonic dysplasia. This condition is characterized by abnormal bone growth that leads to head and face (craniofacial) abnormalities and dwarfism. FGFR1 gene mutations that cause osteoglophonic dysplasia change single amino acids in the FGFR1 protein. The altered FGFR1 protein appears to cause prolonged signaling, which promotes premature fusion of bones in the skull and disrupts the regulation of bone growth in the arms and legs, leading to craniofacial abnormalities and shortened limbs. Because the FGFR1 gene mutations that cause osteoglophonic dysplasia abnormally increase FGFR1 signaling, they are described as "gain-of-function" mutations.

Pfeiffer syndrome

Another "gain-of-function" mutation in the FGFR1 gene can cause Pfeiffer syndrome. This condition is characterized by premature fusion of certain bones in the skull (craniosynostosis), which leads to a misshapen head and distinctive facial features. Affected individuals also have hand and foot abnormalities. The FGFR1 gene mutation that causes this condition changes a single amino acid in the FGFR1 protein; the amino acid proline is replaced with the amino acid arginine at protein position 252 (written as Pro252Arg or P252R). The altered FGFR1 protein appears to cause prolonged signaling, which promotes early fusion of the skull bones and affects the development of bones in the hands and feet.

Other disorders

Several mutations in the FGFR1 gene have been found to cause a form of hypogonadotropic hypogonadism that occurs without an impaired sense of smell. This condition is often called normosmic isolated hypogonadotropic hypogonadism (nIHH). Like the FGFR1 gene mutations that cause Kallmann syndrome (described above), these mutations reduce or eliminate the function of the FGFR1 protein, preventing it from transmitting signals properly.

A shortage of functional FGFR1 disrupts the migration of GnRH-producing nerve cells in the developing brain, which affects the production of sex hormones and leads to delayed or absent puberty. It is unclear why some FGFR1 gene mutations affect the sense of smell (resulting in Kallmann syndrome) and others do not (resulting in nIHH). A few mutations have been found to cause Kallmann syndrome in some people and nIHH in others.

Other cancers

Changes involving the FGFR1 gene have been found in certain cancers. These genetic changes are somatic, which means they are not inherited but instead occur in cells that give rise to the tumor. Gene amplification, which results in an abnormally large number of copies of the FGFR1 gene, occurs in several forms of cancer. These include some cancers of the lung, esophagus, breast, and oral cavity. Additionally, mutations that change single amino acids in the FGFR1 gene have been identified in several types of brain tumor.

Studies suggest that the genetic changes in FGFR1 that are associated with cancer abnormally increase the activity of the FGFR1 protein and enhance its ability to trigger chemical reactions within the cell. The resulting uncontrolled signaling can promote continuous cell growth and division, which is a hallmark of cancer. Amplification of the FGFR1 gene has been associated with a poorer prognosis for some cancers and an increased likelihood that the tumor will spread (metastasize) to other parts of the body.

Other Names for This Gene

• BFGFR
• C-FGR
• CD331
• CEK
• FGFR1_HUMAN
• fibroblast growth factor receptor 1 (fms-related tyrosine kinase 2, Pfeiffer syndrome)
• FLG
• FLJ14326
• FLT2
• FMS-like gene
• FMS-like tyrosine kinase 2
• heparin-binding growth factor receptor 1
• hydroxyaryl-protein kinase
• KAL2
• N-SAM tyrosine kinase
• protein-tyrosine kinase
• tyrosyl protein kinase

Genomic Location

Normal Function

The FGFR2 gene provides instructions for making a protein called fibroblast growth factor receptor 2 (FGFR2). Fibroblast growth factor receptors are related proteins that are involved in important processes such as cell growth and division (proliferation), cell maturation (differentiation), bone development, formation of blood vessels (angiogenesis), wound healing, and embryonic development.

The FGFR2 protein spans the outer membrane surrounding cells, so that one end of the protein remains inside the cell and the other end projects from the outer surface of the cell. This positioning allows the FGFR2 protein to interact with specific growth factors outside the cell and to receive signals that help the cell respond to its environment. When growth factors attach to the FGFR2 protein, the receptor triggers a series of chemical reactions inside the cell that instruct the cell to undergo certain changes, such as maturing to take on specialized functions.

The FGFR2 protein plays an important role in bone growth, particularly during development before birth (embryonic development). For example, this protein signals certain immature cells in the developing embryo to become bone cells and form the head, hands, feet, and other tissues. The protein is also involved in bone remodeling, a normal process in which old bone is broken down and new bone is created to replace it.

There are several slightly different versions (isoforms) of the FGFR2 protein. Specific patterns of these isoforms are found in the body's tissues, and these patterns may change throughout growth and development.

Health Conditions Related to Genetic Changes

Apert syndrome

At least ten mutations in the FGFR2 gene have been found to cause Apert syndrome. This condition causes premature closure of the bones of the skull (craniosynostosis), leading to a misshapen head, distinctive facial features, and brain abnormalities. Affected individuals often have abnormalities of the fingers and toes, hearing and vision problems, and other signs and symptoms.

More than 98 percent of cases of Apert syndrome are caused by one of two mutations in the FGFR2 gene. These mutations change single protein building blocks (amino acids) in the FGFR2 protein. One mutation replaces the amino acid serine with the amino acid tryptophan at protein position 252 (written as Ser252Trp). The other mutation replaces the amino acid proline with the amino acid arginine at position 253 (written as Pro253Arg). These changes are described as "gain-of-function" because they increase the activity of the protein, leading to stronger signaling, which causes cells to mature too quickly. As a result, structures in the body develop abnormally, leading to premature fusion of bones in the skull, hands, and feet and other characteristic features of Apert syndrome.

Beare-Stevenson cutis gyrata syndrome

At least three mutations in the FGFR2 gene have been found to cause Beare-Stevenson cutis gyrata syndrome, a condition that causes craniosynostosis, leading to a misshapen head and distinctive facial features, and a skin abnormality called cutis gyrata. The most common mutation replaces the amino acid tyrosine with the amino acid cysteine at position 375 in the protein (written as Tyr375Cys). The FGFR2 gene mutations that cause Beare-Stevenson cutis gyrata syndrome appear to overactivate signaling by the FGFR2 protein, which promotes the premature fusion of bones in the skull and alters skin development.

Crouzon syndrome

At least 60 mutations in the FGFR2 gene can cause Crouzon syndrome, a condition that causes craniosynostosis, leading to a misshapen head and distinctive facial features. Affected individuals can have vision, hearing, and dental problems related to abnormal skull development. Most of the mutations that cause Crouzon syndrome change single DNA building blocks (nucleotides) in the FGFR2 gene. Insertions and deletions of a small number of nucleotides are also known to cause the disorder. These mutations in the FGFR2 gene appear to overactivate signaling by the FGFR2 protein, which promotes premature fusion of bones in the skull.

Jackson-Weiss syndrome

At least six mutations in the FGFR2 gene have been found to cause Jackson-Weiss syndrome. This condition causes craniosynostosis, leading to a misshapen head and distinctive facial features. Affected individuals also have foot abnormalities. Each of the mutations associated with Jackson-Weiss syndrome changes a single amino acid in a region of the FGFR2 protein known as the IgIII domain, which is critical for receiving signals and interacting with growth factors. The mutations appear to overactivate signaling by the FGFR2 protein, which promotes premature fusion of skull bones and affects development of bones in the feet.

Lacrimo-auriculo-dento-digital syndrome

At least two mutations in the FGFR2 gene have been found to cause lacrimo-auriculo-dento-digital (LADD) syndrome. The main features of LADD syndrome are abnormal tear production, malformed ears with hearing loss, decreased saliva production, small teeth, and hand deformities. A mutation that occurs in some people with LADD syndrome replaces the amino acid alanine with the amino acid threonine at position 628 in the FGFR2 protein (written as Ala628Thr or A628T).

The FGFR2 gene mutations that cause LADD syndrome reduce the FGFR2 protein's ability to trigger chemical signaling within cells when it binds to its growth factor. These defects in cell signaling disrupt cell maturation and development, which results in abnormal formation of glands in the eyes and mouth, the ears, and the skeleton in people with LADD syndrome.

Pfeiffer syndrome

More than 25 mutations in the FGFR2 gene can cause Pfeiffer syndrome, a condition that causes craniosynostosis, leading to a misshapen head and distinctive facial features. People with this condition can also have elbow, hand, or foot abnormalities. The severity of this condition varies widely among affected individuals. Several of the mutations that cause this condition change the number of cysteine amino acids in a critical region of the FGFR2 protein known as the IgIII domain. The remaining mutations affect amino acids other than cysteine or result in an FGFR2 protein that is missing one or more amino acids. These mutations appear to overactivate signaling by the FGFR2 protein, which promotes premature fusion of skull bones and affects the development of bones in the hands and feet.

Breast cancer

MedlinePlus Genetics provides information about Breast cancer

Cholangiocarcinoma

MedlinePlus Genetics provides information about Cholangiocarcinoma

Epidermal nevus

MedlinePlus Genetics provides information about Epidermal nevus

Prostate cancer

MedlinePlus Genetics provides information about Prostate cancer

Other disorders

Mutations in the FGFR2 gene can cause other disorders that affect bone development. FGFR2 gene mutations have been found in individuals with conditions called bent bone dysplasia syndrome and Antley-Bixler syndrome.

Bent bone dysplasia syndrome is characterized by the underdevelopment of certain bones, bent long bones in the arms and legs, low bone mineral density (osteopenia), and distinctive facial features. Signs and symptoms of Antley-Bixler syndrome typically include craniosynostosis, distinctive facial features, arm and leg malformations, and genitourinary abnormalities.

The FGFR2 gene mutations that cause these conditions appear to overactivate signaling by the FGFR2 protein, leading to skeletal abnormalities and other characteristic features of the conditions.

The particular condition that results from FGFR2 gene mutations may be determined by the region of the gene in which the mutation occurs. It is likely that mutations in different regions of the FGFR2 gene have varied effects on the protein, resulting in a range of protein activity and signaling. Changes in other genes or modifications of DNA that do not alter the DNA sequence (epigenetic changes) may also help determine the resulting signs and symptoms. The different factors lead to similar but distinct features of the many conditions associated with FGFR2 gene mutations.

Cancers

Alterations in the activity (expression) of the FGFR2 gene are associated with certain cancers. The altered gene expression may enhance several cancer-promoting cell functions such as cell division (proliferation), cell movement, and the formation of new blood vessels (angiogenesis) that nourish a growing tumor.

The FGFR2 gene is abnormally active (overexpressed) in certain types of stomach (gastric) cancers, and this amplification is associated with a poor disease outcome. Abnormal expression of the FGFR2 gene is also found in patients with prostate cancer. A shift in the expression of two specific FGFR2 isoforms, IIIb and IIIc, appears to correlate with prostate cancer progression. This change in expression is complex, however, and varies depending on the type of prostate tumor. More advanced tumors may show an increase in the IIIb isoform, while other prostate tumors show a decrease in IIIb but an increase in IIIc. Altered FGFR2 gene expression is also associated with ovarian, breast, cervical, endometrial, pancreatic, lung, and head and neck cancers.

Other Names for This Gene

• bacteria-expressed kinase
• BEK
• BEK fibroblast growth factor receptor
• BEK protein tyrosine kinase
• BFR-1
• CD332
• CEK3
• CFD1
• ECT1
• FGF receptor
• FGFR2_HUMAN
• K-SAM
• keratinocyte growth factor receptor
• KGFR
• protein tyrosine kinase, receptor like 14
• TK14
• TK25
• tyrosylprotein kinase

Genomic Location