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Disease Information

Summary

FG syndrome type 1 is a genetic condition that affects many parts of the body and occurs almost exclusively in males. People with FG syndrome type 1 frequently have intellectual disability ranging from mild to severe, hypotonia, constipation and/or anal anomalies, a distinctive facial appearance, broad thumbs and great toes, a large head compared to body size (relative macrocephaly), and abnormalities of the corpus callosum. Medical problems including heart defects, seizures, undescended testicle, and an inguinal hernia have also been reported in some affected individuals. FG syndrome type 1 is inherited in an X-linked recessive pattern. Individualized early intervention and educational services are important so that each child can reach their fullest potential. FG syndrome 1 is a genetic condition that affects many parts of the body and occurs almost exclusively in males. "FG" represents the surname initials of the first family diagnosed with the disorder. FG syndrome 1 affects intelligence and behavior. Almost everyone with the condition has intellectual disability, which ranges from mild to severe. Affected individuals tend to be friendly, inquisitive, and hyperactive, with a short attention span. Compared to people with other forms of intellectual disability, their socialization and daily living skills are strong, while verbal communication and language skills tend to be weaker. The physical features of FG syndrome 1 include weak muscle tone (hypotonia), broad thumbs, and wide first (big) toes. Abnormalities of the tissue connecting the left and right halves of the brain (the corpus callosum) are also common. Most affected individuals have constipation, and many have abnormalities of the anus such as an obstruction of the anal opening (imperforate anus). People with FG syndrome 1 also tend to have a distinctive facial appearance including small, underdeveloped ears; a tall, prominent forehead; and outside corners of the eyes that point downward (down-slanting palpebral fissures). Additional features seen in some people with FG syndrome 1 include widely set eyes (hypertelorism), an upswept frontal hairline, and a large head compared to body size (relative macrocephaly). Other health problems have also been reported, including heart defects, seizures, undescended testes (cryptorchidism) in males, and a soft out-pouching in the lower abdomen (an inguinal hernia). FG syndrome 1 is inherited in an X-linked pattern. Mutations in a gene called MED12 appear to be the most common cause of the disorder.

About FG syndrome 1

Many rare diseases have limited information. Currently, GARD aims to provide the following information for this disease:

  • Symptoms:May start to appear during Pregnancy and as a Newborn.
  • Cause:This disease is caused by a change in the genetic material (DNA).
  • Organizations:Patient organizations dedicated to this rare disease are available on GARD, or you may contact a GARD Information Specialist for additional information.
  • Categories:Genetic diseases(Genetic diseases affect the DNA, or genetic instructions, which directs how tissues, organs, and body systems function.)Neurological diseases(Neurological diseases affect the brain, spinal cord, cranial nerves, autonomic nerves, or other peripheral nerves.)Gastrointestinal diseases(Gastrointestinal diseases, or digestive diseases, affect the esophagus, stomach, small intestine, large intestine, liver, gallbladder, or pancreas.)Birth defects(Birth defects are structural changes present at birth that can affect almost any part of the body, including how the body looks, works, or both.)

Resource(s) for Medical Professionals and Scientists on This Disease:

  • GeneReview provides clinical information on genetic diseases, including diagnosis, treatment, and genetic counseling.
  • MONDO provides GARD with information for this disease.
  • Orphanet provides GARD with information for this disease.
  • RARe-SOURCE™ offers rare disease gene variant annotations and links to rare disease gene literature.

Resource(s) for Medical Professionals and Scientists on This Disease:

  • GeneReview provides clinical information on genetic diseases, including diagnosis, treatment, and genetic counseling.
  • MONDO provides GARD with information for this disease.
  • Orphanet provides GARD with information for this disease.
  • RARe-SOURCE™ offers rare disease gene variant annotations and links to rare disease gene literature.

About FG syndrome 1

Many rare diseases have limited information. Currently, GARD aims to provide the following information for this disease:

  • Symptoms:May start to appear during Pregnancy and as a Newborn.
  • Cause:This disease is caused by a change in the genetic material (DNA).
  • Organizations:Patient organizations dedicated to this rare disease are available on GARD, or you may contact a GARD Information Specialist for additional information.
  • Categories:Genetic diseases(Genetic diseases affect the DNA, or genetic instructions, which directs how tissues, organs, and body systems function.)Neurological diseases(Neurological diseases affect the brain, spinal cord, cranial nerves, autonomic nerves, or other peripheral nerves.)Gastrointestinal diseases(Gastrointestinal diseases, or digestive diseases, affect the esophagus, stomach, small intestine, large intestine, liver, gallbladder, or pancreas.)Birth defects(Birth defects are structural changes present at birth that can affect almost any part of the body, including how the body looks, works, or both.)

Causes

What Causes This Disease?

Genetic Mutations

Changes in your genes (also called variants) cause FG syndrome 1.

Genes are sections of DNA that contains instructions that help the body grow, develop, and function. A genetic variant is a change in your DNA's order. Parents may pass variants to their children, or they may occur randomly. They may result from viruses, environmental factors, such as UV radiation, or a combination of causes.

Most genetic variants do not cause disease. However, some can affect how a gene works and interfere with the body's normal functions. A pathogenic variant is one that causes disease.

If you think you may have this disease, collect your family health history (CDC). It may help you and your medical team to know about family members who have had the disease or similar symptoms and when those symptoms first appeared.

Read more about genetic disorders (NIH MedlinePlus). 

Genetic Mutations

Changes in your genes (also called variants) cause FG syndrome 1.

Genes are sections of DNA that contains instructions that help the body grow, develop, and function. A genetic variant is a change in your DNA's order. Parents may pass variants to their children, or they may occur randomly. They may result from viruses, environmental factors, such as UV radiation, or a combination of causes.

Most genetic variants do not cause disease. However, some can affect how a gene works and interfere with the body's normal functions. A pathogenic variant is one that causes disease.

If you think you may have this disease, collect your family health history (CDC). It may help you and your medical team to know about family members who have had the disease or similar symptoms and when those symptoms first appeared.

Read more about genetic disorders (NIH MedlinePlus). 

Known Genetic Mutations

FG syndrome 1 is caused by genetic mutations in the following known gene(s):

MED12
Learn more about these genes by searching them on the National Library of Medicine (NLM).

Given these known genetic mutation(s), you may want to ask your health care team if genetic testing is right for you. Genetic tests are laboratory tests that use samples of blood, saliva, or other tissues to help identify changes in genes, chromosomes, or proteins. Genetic testing can help confirm or rule out a suspected genetic disease or can provide other useful information to your health care team. Learn more about genetic testing from the National Human Genome Research Institute (NHGRI).

Can diseases be passed down from parent to child?

A biological parent can sometimes pass down genetic changes, called mutations, that cause a disease or increase the chances of developing it. This is called inheritance. Knowing if other family members have had the disease, also known as your family health history, can give your medical team important information. The Surgeon General offers a tool to help you collect your family health history.

X-Linked

X-linked inheritance means the genetic mutation is located on the X chromosome, one of the sex chromosomes. The male sex chromosome pair consists of one X and one Y chromosome (XY). The female sex chromosome pair consists of two X chromosomes (XX). Because males have just one X chromosome, it takes only one copy of the mutated gene to cause the disease. Females that have one copy of the mutated gene may have symptoms similar to those experienced by affected males, but usually have less severe symptoms, or no symptoms at all.

Female parents with one X-linked mutated gene have a 50% chance of passing on the mutation to each of their biological children. Male parents with an X-linked mutated gene will pass on the mutation to all their female children but cannot pass the mutation on to their male children.

Learn more about inheritance patterns from the National Library of Medicine (NLM).

X-Linked

X-linked inheritance means the genetic mutation is located on the X chromosome, one of the sex chromosomes. The male sex chromosome pair consists of one X and one Y chromosome (XY). The female sex chromosome pair consists of two X chromosomes (XX). Because males have just one X chromosome, it takes only one copy of the mutated gene to cause the disease. Females that have one copy of the mutated gene may have symptoms similar to those experienced by affected males, but usually have less severe symptoms, or no symptoms at all.

Female parents with one X-linked mutated gene have a 50% chance of passing on the mutation to each of their biological children. Male parents with an X-linked mutated gene will pass on the mutation to all their female children but cannot pass the mutation on to their male children.

Learn more about inheritance patterns from the National Library of Medicine (NLM).

When Do Symptoms of FG syndrome 1 Begin?

Symptoms of this disease may start to appear during Pregnancy and as a Newborn.

The age symptoms may begin to appear differs between diseases. Symptoms may begin in a single age range, or during several age ranges. The symptoms of some diseases may begin at any age. Knowing when symptoms may have appeared can help medical providers find the correct diagnosis.
  1. Prenatal Selected
    Before Birth
  2. Newborn Selected
    Birth-4 weeks
  3. Infant
    1-23 months
  4. Child
    2-11 years
  5. Adolescent
    12-18 years
  6. Adult
    19-65 years
  7. Older Adult
    65+ years
Symptoms may start to appear during Pregnancy and as a Newborn.
This information comes from Orphanet

Symptoms

You may have one or more symptoms, and they may be mild or severe. Having some or all of these symptoms does not mean you have this disease. Only a health care provider can diagnose you.

Common

Many people have these, but not everyone.

  • Abnormality of the cerebellum (Abnormal cerebellum morphology)
  • Abnormality of the large intestine (Abnormal large intestine morphology)
  • Abnormality of the sternum (Abnormal sternum morphology)
  • An opening in the wall separating the top two chambers of the heart (Atrial septal defect)
  • Aplasia/Hypoplasia of the corpus callosum
  • Broad neck
  • Broad toe
  • Cross-eyed (Strabismus)
  • Cupped ear
  • Delayed speech and language development
  • Dental crowding
  • Downward slanting of the opening between the eyelids (Downslanted palpebral fissures)
  • Drooling
  • Flat feet (Pes planus)
  • Flat head syndrome (Plagiocephaly)
  • Frontal upsweep of hair
  • Full lips (Thick vermilion border)
  • Fused teeth
  • Generalized low muscle tone in neonate (Generalized neonatal hypotonia)
  • Global developmental delay
  • High forehead
  • High palate
  • Hypermobility of all joints (Generalized joint hypermobility)
  • Hypospadias
  • Increased size of skull (Macrocephaly)
  • Inguinal hernia
  • IQ between 34 and 49 (Moderate intellectual disability)
  • Limited elbow extension and supination
  • Little lower jaw (Micrognathia)
  • Long philtrum
  • Malrotation of colon
  • Narrowing of passageway from outer ear to middle ear (Stenosis of the external auditory canal)
  • Optic nerve hypoplasia
  • Premature birth
  • Prominent back of the skull (Prominent occiput)
  • Prominent nose
  • Pyloric stenosis
  • Short stature
  • Slender build
  • Small ears (Microtia)
  • Small pituitary gland
  • Undescended testes (Cryptorchidism)
  • Ventriculomegaly
  • Wide based walk (Broad-based gait)
  • Wide mouth
  • Wide-set eyes (Hypertelorism)
  • Widely patent fontanelles and sutures
  • Zygomatic flattening (Malar flattening)

Uncommon

Some people have these, but most people do not.

  • Abnormal social behavior
  • Abnormality of the thumb (Abnormal thumb morphology)
  • Absent anus (Anal atresia)
  • Acid reflux (Gastroesophageal reflux)
  • Attention deficit (Attention deficit hyperactivity disorder)
  • Blockage of the rear opening of the nasal cavity (Choanal atresia)
  • Clinodactyly of the 2nd finger
  • Constipation
  • Craniosynostosis
  • Facial wrinkling
  • Finger syndactyly
  • Increased blood pressure in blood vessels of lungs (Pulmonary arterial hypertension)
  • Mitral valve prolapse
  • Narrowing of aorta (Coarctation of aorta)
  • Obsessive compulsive behavior (Compulsive behaviors)
  • Open mouth
  • Progressive flexion contractures
  • Seizure
  • Sensorineural hearing impairment
  • Short chin
  • Single transverse palmar crease
  • Spinal dimple (Sacral dimple)
  • Too much cerebrospinal fluid in the brain (Hydrocephalus)
  • Umbilical hernia
This information comes from the Human Phenotype Ontology (HPO)

Navigating Health Care Decisions

On average, it can take more than six years to receive an accurate diagnosis. Many primary care providers (PCPs) may not be familiar with rare diseases, and patients often need to visit multiple specialists or seek second opinions to get answers.

If a diagnosis remains unclear, visiting a multidisciplinary care center or university hospital may help. These centers bring together teams of specialists who can work together to evaluate symptoms and coordinate a diagnosis. This team-based approach is also helpful after a diagnosis, when managing care for rare diseases.

Because only about 5% of rare diseases have FDA-approved treatments, finding the right healthcare team to manage your symptoms and overall health is essential. People living with rare diseases often face challenges such as delayed diagnosis, limited treatment options, and difficulty accessing knowledgeable providers. Building a care team that understands your needs can make a significant difference in your quality of life.

Your Health Care Team

Why is building the right health care team important?

Building the right health care team is key to the diagnosis, treatment, and management of your long-term health journey living with a rare disease. Start by choosing a primary care provider (PCP). Your PCP will be your main point of contact and help coordinate care with other medical professionals. Your PCP may order tests or refer you to specialists. To find a PCP near you, use the Medicare provider search tool and enter your location and “Primary Care Provider.”

Seeing multiple specialists is important for people with rare diseases because these conditions often affect many parts of the body and require care from doctors with different expertise. Most primary care providers may not be familiar with rare diseases, so involving specialists can lead to a more accurate diagnosis and better care. A coordinated team approach ensures that all symptoms are addressed and that care is well-managed. It can also connect patients with the latest research or treatment options.

A PCP that specializes in the care of children is called a pediatrician. Use this tool by the American Academy of Pediatrics to find a pediatrician in your area by inputting your location.

These specialists may help in the diagnosis, management, and treatment of FG syndrome 1:

Neurologists are doctors with specialized training in diagnosing and treating conditions that affect the brain, spinal cord, and nerves. These parts of the nervous system help control how the body moves, feels, and thinks. Neurologists often care for people with seizures, memory problems, muscle weakness, movement disorders, and inherited conditions such as muscular dystrophies. To better understand a person's symptoms, neurologists may use imaging tests that show the brain or spine, or tests that measure the brain’s electrical activity.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory provided by the American Board of Psychiatry and Neurology to find a specialist. 
Gastroenterologists are doctors trained to diagnose and treat diseases that affect the digestive system, including the esophagus, stomach, intestines, pancreas, gallbladder, and liver. To evaluate digestive health, they may use flexible tubes with cameras called endoscopes to look inside the digestive tract. They treat conditions such as acid reflux, inflammatory bowel disease, liver disease, and digestive cancers. If you have ongoing digestive symptoms like abdominal pain, difficulty swallowing, or changes in bowel habits, a gastroenterologist can help find the cause and recommend treatment.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory provided by the American College of Gastroenterology to find a specialist.
Geneticists are doctors trained to diagnose and manage conditions caused by genetic changes, birth defects, or metabolic disorders. Metabolic disorders affect how the body makes or uses energy. Geneticists often work alongside genetic counselors to review family history, discuss genetic risks, explain testing options, and interpret genetic test results. They help people understand how inherited conditions may affect them and their families.

You may want to consider bringing a copy of your medical history and a list of any medications to your appointment.

Ask your primary care provider for a referral or use this directory provided by the American College of Medical Genetics and Genomics to find a specialist.

Multidisciplinary Care Centers

Is It Time to Get a Second Opinion or Specialized Evaluation?

If you've visited your PCP, met with specialists, and undergone the recommended tests, but are still searching for a diagnosis, it may be time to visit an academic medical center or, for pediatric patients, a children's hospital. Academic medical centers and children's hospitals, often called multidisciplinary care centers, typically bring together specialists from different fields to work together on complex cases like rare diseases.

Multidisciplinary care centers may offer more coordinated care and be involved in clinical research, which may help reduce the time to diagnosis and provide access to emerging diagnostic tools. Specialists at these centers may have a deeper understanding of rare diseases and serve as a resource when you'd like a second opinion, particularly when test results or treatment plans are not delivering expected results.

Find hospitals that may partner with medical schools and programs in your area. 

Children’s hospitals and large teaching hospitals may also offer dedicated specialists and programs for pediatric patients with undiagnosed or rare diseases. These programs bring pediatric experts together in one place and may provide more coordinated care for your child.

Search for children's or university hospitals in your area.

Rare Disease Experts

How can you find a rare disease expert?

If a diagnosis, care management, or treatment plan remains unclear despite extensive efforts by your PCP and specialists, it may be time to find a rare disease expert for your disease, if available. A rare disease expert is a medical provider that has knowledge or training on specific rare disease(s), but there may only be a few experts in your state, region, or country. Rare disease experts may work at large research or teaching hospitals, sometimes called centers of excellence. Centers of Excellence commit to sharing knowledge and best practices that can lead to improved care and treatment for individuals living with a rare disease. 

You can also contact a GARD Information Specialist for help finding experts, centers of excellence, or clinics that focus on your disease.
You can ask your care providers for help finding an expert or use directory tools to search for experts near you. The National Organization for Rare Disorders (NORD) maintains a list of rare disease centers with experts that work together to find treatments and cures for a broad range of rare diseases. Search NORD's Center Directory to find experts near you.

Find Your Community

How can patient organizations help?

Patient organizations can help patients and families connect. They build public awareness of the disease and are a driving force behind research to improve patients' lives. They may offer online and in-person resources to help people live well with their disease. Many collaborate with medical experts and researchers.

Services of patient organizations differ, but may include:

  • Ways to connect to others and share personal stories
  • Easy-to-read information
  • Up-to-date treatment and research information
  • Patient registries
  • Lists of specialists or specialty centers
  • Financial aid and travel resources


Please note: GARD provides organizations for informational purposes only and not as an endorsement of their services. Contact a GARD Information Specialist for more information on organizations that may be dedicated to this disease. Please contact an organization directly if you have questions about the information or resources it provides.


View GARD's criteria for including patient organizations, which can be found under the FAQs on our About GARD page. Request an update or to have your organization added to GARD. 

Patient Organizations

3 Organizations

Simons Searchlight

People With

FG syndrome 1

Helpful Links
Country

United States

National Organization of Disorders of the Corpus Callosum

People With

FG syndrome 1

Country

United States

Pull-thru Network

People With

FG syndrome 1

Country

United States

OrganizationPeople WithHelpful LinksCountry
Simons SearchlightFG syndrome 1Research RegistryUnited States
National Organization of Disorders of the Corpus CallosumFG syndrome 1United States
Pull-thru NetworkFG syndrome 1United States

Participate in Research

Clinical studies are a part of clinical research and play an important role in medical advances for rare diseases. Through clinical studies, researchers may ultimately uncover better ways to treat, prevent, diagnose, and understand human diseases.

What Are Clinical Studies?

Clinical studies are medical research involving people as participants. There are two main types of clinical studies:

  1. Clinical trials determine if a new test or treatment for a disease is effective and safe by comparing groups receiving different tests/treatments.
  2. Observational studies involve recording changes over time among a specific group of people in their natural settings.

Learn more about clinical trials from this National Institutes of Health webpage.

Why Participate in Clinical Studies?

People participate in clinical trials for many reasons. People with a disease may participate to receive the newest possible treatment and additional care from clinical study staff as well as to help others living with the same or a similar disease. Healthy volunteers may participate to help others and to contribute to moving science forward.

To find the right clinical study we recommend you consult your doctors, other trusted medical professionals, and patient organizations. Additionally, you can use ClinicalTrials.gov to search for clinical studies by disease, terms, or location.

What if There Are No Available Clinical Studies?

ResearchMatch helps connect people interested in research studies  with researchers from top medical centers across the United States. Anyone from the U.S. can register with this free program funded by NIH. Researchers from participating institutions use the database to search for and invite patients or healthy volunteers who meet their study criteria to participate.

Why may you want to consider joining the All of Us Research Program?

The All of Us Research Program is inviting 1 million people from all backgrounds across the U.S. to help build one of the most diverse health databases in history. Researchers will use the data to learn how our biology, lifestyle, and environment affect health. This may one day help them find ways to treat and prevent diseases.

ClinicalTrials.gov, an affiliate of NIH, provides current information on clinical research studies in the United States and abroad. Talk to a trusted doctor before choosing to participate in any clinical study. We recommend checking this site often and searching for studies with related terms/synonyms to improve results.
Search ClinicalTrials.gov for this disease.
GARDGenetic and Rare Diseases
Information Center
Contact a GARD Information Specialist if you need help finding more information on this rare disease or available clinical studies. Please note that GARD cannot enroll individuals in clinical studies.
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Sources & References

Last Updated: September 2026