Introduction

Fraser syndrome is a rare genetic disorder that affects multiple organs and systems in the body. This rare condition typically affects the eyes, fingers, toes, kidneys, and genitals. Some of the most common features include:¹

• Cryptophthalmos (hidden eyes): The eyelids are fused shut, covering the eyeball
• Syndactyly: Fingers or toes are fused together
• Abnormalities of the genitals and urinary tract
• Kidney malformations
• Laryngeal defects that can affect breathing
• Ear malformations

The severity of these symptoms can vary widely among affected individuals, even within the same family.

The Genetic Basis of Fraser Syndrome 

Fraser syndrome is an autosomal recessive disorder.¹ This means that for a child to be affected, they must inherit two copies of the mutated gene – one from each parent. Parents who carry one copy of the mutated gene are called carriers. They typically don't show any signs of the condition but can pass the gene to their children.

When both parents are carriers, there's a 25% chance with each pregnancy that their child will have Fraser syndrome, a 50% chance the child will be a carrier like the parents, and a 25% chance the child will neither have the condition nor be a carrier.

Genes involved in Fraser Syndrome 

Research has identified several genes associated with Fraser syndrome. The primary genes involved are:²

• FRAS1 (Fraser Syndrome 1)
• FREM2 (FRAS1-Related Extracellular Matrix Protein 2)
• GRIP1 (Glutamate Receptor Interacting Protein 1)

These genes play crucial roles in embryonic development, particularly in the formation of the extracellular matrix – a network of proteins and other molecules that provides structural and biochemical support to surrounding cells.

FRAS1 Gene

The FRAS1 gene provides instructions for making a protein that is essential for the adhesion of epithelial cells to the underlying layer of connective tissue during embryonic development.³ This protein is particularly important in the development of the skin, kidneys, and eyes.

Mutations in the FRAS1 gene can disrupt the formation of this crucial protein, leading to the characteristic features of Fraser syndrome. These mutations can vary, including:

• Deletions: Parts of the gene are missing.
• Insertions: Extra DNA is inserted into the gene.
• Point mutations: A single DNA building block (nucleotide) is changed.
• Splice site mutations: These affect how the gene's instructions are read, potentially leading to an abnormal protein.

These mutations can result in:

• Complete absence of the FRAS1 protein
• Production of an abnormally short, non-functional protein
• Production of a full-length but dysfunctional protein

The absence or dysfunction of the FRAS1 protein leads to improper adhesion between tissue layers during development, resulting in many of the characteristic features of Fraser syndrome.

FREM2 Gene

The FREM2 gene is closely related to FRAS1 and also plays a role in the formation of the extracellular matrix.⁴ The protein produced by this gene interacts with the FRAS1 protein, forming a complex that is crucial for proper embryonic development.

Mutations in FREM2 can lead to similar outcomes as FRAS1 mutations, resulting in the features of Fraser syndrome. The types of mutations can be similar to those seen in FRAS1. 

Approximately 10-20% of Fraser syndrome cases are attributed to mutations in the FREM2 gene.⁴

GRIP1 Gene

The GRIP1 gene is slightly different from FRAS1 and FREM2. It provides instructions for making a protein that helps anchor other proteins, including FRAS1 and FREM2, to the cell membrane.⁵ This anchoring is crucial for these proteins to function correctly in the extracellular matrix. Mutations in GRIP1 can indirectly affect the function of FRAS1 and FREM2 proteins; these mutations can disrupt the anchoring process, leading to misplacement or dysfunction of the FRAS1 and FREM2 proteins. 

About 5-10% of Fraser syndrome cases are linked to mutations in the GRIP1 gene.⁵

How These Genetic Mutations Cause Fraser Syndrome

The proteins produced by FRAS1, FREM2, and GRIP1 genes work together to form a complex in the basement membrane, a specialised structure in the extracellular matrix.² This complex is crucial for the proper adhesion of the epidermis (outer layer of skin) to the underlying dermis during embryonic development.

When mutations occur in any of these genes, the complex doesn't form correctly. This can lead to:⁵

• Skin fragility: The epidermis may separate from the dermis, leading to blistering and other skin abnormalities.
• Eye defects: The failure of proper adhesion can prevent the eyelids from separating during development, leading to cryptophthalmos.
• Kidney problems: The proteins are important in kidney development, and their absence can lead to various kidney malformations.
• Syndactyly: The failure of proper tissue separation during limb development can cause fingers or toes to remain fused.
• Genital and urinary tract abnormalities: These proteins play a role in the development of these systems, and their dysfunction can lead to various malformations.

Other Genetic Factors

While FRAS1, FREM2, and GRIP1 are the primary genes associated with Fraser syndrome, research suggests that other genes may also be involved6:

• FREM1: Another member of the FRAS-FREM protein complex, mutations in this gene have been associated with a related condition called Manitoba oculotrichoanal syndrome.
• FRAS1, FREM2, and GRIP1 regulatory genes: Mutations in genes that regulate the expression of FRAS1, FREM2, and GRIP1 could potentially lead to Fraser syndrome, though this is an area of ongoing research.
• Modifier genes: These are genes that can influence the severity and presentation of Fraser syndrome when mutations are present in the primary genes.

Implications for Treatment and Research

Understanding the genetic causes of Fraser syndrome is crucial for several reasons:²

• Improved diagnosis: Genetic testing can provide a definitive diagnosis, which is particularly important in cases where the physical features are less pronounced.
• Genetic counselling: Families with a history of Fraser syndrome can receive informed genetic counselling about the risks of having affected children in future pregnancies.
• Potential treatments: While there is currently no cure for Fraser syndrome, understanding its genetic basis opens up possibilities for future gene therapies or treatments that target the underlying molecular mechanisms.
• Research directions: Knowing which genes are involved helps researchers focus their efforts on understanding how these genes function and interact, potentially leading to new insights into embryonic development and related disorders.

Summary 

Fraser syndrome is a complex genetic disorder caused by mutations in genes crucial for embryonic development. While the condition is rare, understanding its genetic causes provides valuable insights into fundamental developmental processes and opens up avenues for improved diagnosis and potential future treatments.

As our understanding of genetics continues to advance, we may uncover additional genes involved in Fraser syndrome or develop more sophisticated methods for genetic testing and analysis. This ongoing research not only benefits those affected by Fraser syndrome but also contributes to our broader understanding of human development and genetic disorders.

For families affected by Fraser syndrome, genetic counseling and support from medical professionals are crucial. While the genetic causes of the condition are complex, this knowledge empowers families to make informed decisions and helps medical professionals provide the best possible care for affected individuals.

FAQs

Is Fraser syndrome hereditary?

Fraser syndrome is inherited in an autosomal recessive pattern, meaning a child must inherit one mutated gene from each parent to be affected. While there is no cure for Fraser syndrome, corrective surgeries may be available to address some of the associated malformations, depending on their severity.

What genetic mutation causes Angelman syndrome?

Angelman syndrome is caused by a genetic mutation on chromosome 15, specifically affecting the UBE3A gene. Typically, individuals inherit one copy of this gene from each parent, and both copies are active in many parts of the body. However, in cases of Angelman syndrome, only one copy of the gene is active in certain areas of the brain.

What causes frasier syndrome?

Mutations in the WT1 gene lead to Frasier syndrome. The WT1 gene encodes a protein that acts as a transcription factor by binding to specific DNA regions to regulate the activity of other genes.

What are the genetic causes of disability syndrome?

The two most common genetic causes of intellectual disabilities are Down syndrome and Fragile X syndrome. Down syndrome is the most prevalent genetic origin of intellectual disability, occurring in approximately 1 in every 800 births.

What are the odds of getting Fraser syndrome?

Fraser syndrome is an autosomal recessive condition, and genetic counselling is recommended for at-risk families (where both parents are carriers of a disease-causing mutation). They should be informed of the 25% likelihood that each pregnancy could result in an affected child.

Can Fraser syndrome be detected before birth?

Fraser syndrome is often identified through ultrasound around the 18-week mark of gestation. Prenatal ultrasonographic diagnosis may be conducted if there is a family history of the disorder or if known gene mutations are present in the parents.