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What is Fragile X?

Fragile X is a family of inherited genetic conditions, in particular Fragile X Syndrome. The gene which causes Fragile X Syndrome can also impact carriers of the genetic anomaly.

What is Fragile X Syndrome?

Fragile X Syndrome is the most common inherited form of intellectual, developmental and learning disability and autism. The genetic issue that causes Fragile X Syndrome lies on a single gene on the X chromosome. If this gene is fully mutated, the gene cannot fulfil its normal function any longer, and the protein it encodes cannot be produced anymore. The lack of the fragile X protein has various effects in different cells of the body, in particular in the brain cells, the neurons.

The name of the Fragile X gene/protein is Fragile X Messenger Ribonucleoprotein 1, abbreviated FMR1/FMRP.

Fragile X Syndrome is a rare condition, it occurs only in about 1:4000 males and about 1:6000 females.

What are the symptoms of Fragile X Syndrome?

People with Fragile X Syndrome have a very friendly nature and are pleasant, lovely, helpful and enjoyable.

However, the genetic condition means a substantial burden for them. Almost all affected males and a lot of females with Fragile X Syndrome need help in all stages of life.

The following symptoms of Fragile X Syndrome mostly apply to males, but also to some females. Special characteristics of females with Fragile X Syndrome are listed at the end. Note that normally not all of the listed symptoms will actually apply:

Physical symptoms:
  • Newborns: difficulties with sucking/breastfeeding
  • Strong salivary flow, often opened mouth
  • Gastric reflux
  • Low muscle tone (“Muscular hypotonia”)
  • Joint hypermobility
  • Ear infections in early childhood
  • Difficulties with sense of balance
  • Large prominent ears
  • Starting at adolescent’s age: prolonged face
  • Males: enlarged testicles (“Macroorchidism”), particularly after puberty
  • Single transverse palmar crease (STPC)
  • Epileptic seizures (ca. 10-25% of males and less than 8% of females, normally stopping during puberty)
  • Rarely: Mitral valve prolapse

Developmental symptoms
  • Late or no crawling
  • Late sitting and walking
  • Delayed development of social skills, how to play with other children
  • Delayed or no speech development
  • Speech perseveration (persistence in communication about certain thought content)
  • Echolalia (repeating words or sentences many times)
  • Long lasting incontinence

Behavioural symptoms
  • Hyperactivity
  • Hand flapping, fluttering with arms
  • Hand biting
  • Bolting food
  • Anxiety in new environments
  • Anxiety in stress situations
  • Social anxiety, social shyness
  • Avoiding direct eye contact
  • Autistic behaviours
  • Chewing on things, e.g. shirt collars
  • Putting everything in mouth
  • Waking up early in the morning
  • Emotionally unstable (fast mood swing)
  • Love to play with water
  • Love to play with switches
  • Love to turn things like spinners, etc.
  • Love to watch things turn like washing machines
  • Do not foresee dangerous situations (e.g., when crossing a road)
  • Love to play with automatic doors
  • Disinterest in environment, lack of curiosity in some situations

Symptoms specific to females affected by Fragile X Syndrome
  • Social anxiety and shyness
  • Depression
  • Learning issues (including deficits in attention, sequencing, mathematical abilities and spatial orientation)
  • Fine-motor coordination difficulties (e.g. handwriting, sewing)
  • Gross-motor coordination difficulties (e.g. uneven gait in running, difficulties in throwing and catching a ball, proprioception, etc.)
  • Sensory integration issues/sensory overload

Will my child with Fragile X Syndrome have a normal life expectancy?

It is believed that people with Fragile X Syndrome have a normal life expectancy. However, often due to reduced communication skills, one must be aware that the affected people might need help in recognising and reporting health problems, in particular, but not limited to, in adulthood.

Is there a cure for Fragile X Syndrome?

No. There have been various attempts to influence the effects of the missing protein, but so far, no positive outcomes of significance have been found. Due to the complexity of the underlying alterations in the proteomics caused by Fragile X Syndrome, a pharmacological “cure” in its actual meaning is unlikely to be found.

Other theoretically thinkable interventions like the “gene-scissor” CRISPR/Cas suffer other fundamental barriers in application.

Some pharmacological treatments are available for the symptoms a person might experience (e.g. anxiety; ADHD; gastro-intestinal problems), none of them without side effects that one has to consider.

We will add a special section on Fragile X research in the future on

What therapies are recommended?

It is very important to start giving the child support therapies as soon as the diagnosis has been reached. In some countries, there are early intervention programs for children with special needs that should be consulted. One of the most important therapies is speech and language therapy, as it will help the child communicate with the environment. Children with Fragile X Syndrome often don’t dare to begin speaking, as they think they can’t do it. Speech therapists can help overcome these anxieties. Other important therapies include physiotherapy, for example in addressing poor muscle tone, mobility issues and proprioception; behavioural therapy, addressing sensory integration issues and triggers for outbursts; occupational therapies; and educational therapies.

Where can I find help in my country?

We recommend first consulting a national Fragile X family association, if that is available in your country. However, there may not be such an organisation yet, but an organisation in another country speaking the same language might be worth contacting. Sometimes, the social and/or health system may provide support for children with disabilities.

[To be included: Link to list of FraXI members and other FX family organisations] Why is the genetic condition called “Fragile X Syndrome”?

Why is the genetic condition called “Fragile X Syndrome”?

The gene that causes Fragile X Syndrome is located on the X chromosome. Until the gene was identified in 1991, it was only possible to diagnose the condition under the microscope, where the X chromosome then appears as if it is fragile.

Photo courtesy of Professor Christine J Harrison, Paterson Laboratories, Christie Hospital, Manchester.

How is Fragile X inherited?

Fragile X develops over multiple generations. For some still unknown reasons, a tiny bit of the gene that can cause Fragile X Syndrome eventually may mutate with a specific piece growing inside the gene from one generation to the next. This process can only happen from a mother to her offspring. Once the extension of the gene has grown to a certain size, the premutation of the gene turns into a full mutation in the next generation, and the gene does not function anymore, resulting in Fragile X Syndrome.

Mothers have two X chromosomes, and therefore can either forward the X chromosome with the healthy gene or the mutated one (premutated or fully mutated) to her children. If the gene was already fully mutated, or if it was severely premutated, the child will have a fully mutated gene and have Fragile X Syndrome.

Fathers give their sons a Y chromosome and therefore any mutation on their X chromosome will have no effect on their sons. Fathers give their daughters their X chromosome, and therefore, if the relevant gene is affected, fathers will pass it on to all their daughters. However, the mutation does not grow if forwarded by fathers, and therefore it will not cause Fragile X Syndrome in the father’s daughters: only the premutation is inherited.

Further reading:

Where can I get help for my child?

First of all, it is important to seek help. It is very likely that you will run into one or two problems, and there’s nothing bad about looking for support. You are not alone. Experts and support organisations (like your country’s Fragile X association) can offer help and support.

If you have friends and family members, try to involve them. Explain the situation to them, tell them what you know about Fragile X Syndrome (FXS) and the character of your child. If they can spend some time with your child (which will then give you some time for yourself), that can be of great help!

It can be difficult to find professional help from doctors, as many will not know anything about FXS. A paediatrician may only experience one child with FXS in his or her whole practice career. It is more likely that you will find a therapist who may have seen a child with FXS before, as they are specialists in children with special needs.

Don’t wait to begin speech therapy if your child doesn’t seem to start speaking. And even then, if their speech is hard to understand or is further delayed, try to find a good speech and language therapist.

What is important in kindergarten/preschool?

It is very important to prepare staff before the child enters kindergarten. They need to know how the child “functions”, what should be avoided, what needs to be prepared.

There are several important points:

  1. The group should not be too big. The less noise, mess and confusion, the better.
  2. Normally, a support worker should be there for the child. It is not always necessary to have 1:1 support, but there should be someone there for the child if problems occur.
  3. It is important to have a quiet space, perhaps a separate room or a hallway, somewhere to be able to go to and calm the child down in case of excitement.
  4. It is very important to structure the day for the affected child. Routines are important.
  5. Food and drinks are not always requested independently by the child, it should be taken care that the child gets enough to eat and drink.
  6. Generally, the teacher or support worker should keep an eye on the child in all situations as the child will not always speak up for themselves.
  7. Children with Fragile X Syndrome (FXS) should not be overwhelmed with tasks. What is easy for a “normal” child may already be a difficult task for a child with FXS.
  8. Instructions should be broken down, and the teacher/support worker should check the child has understood. Simple sentences should be used, avoiding subordinate clauses.

What needs to be done to have a good education?

Actually, all the points above in regard to pre-school also hold true for primary education. Having an ‘About Me’ statement for the child, that explains how best to support them in their learning, is a real help. An educational or occupational therapist can help with this.

The choice of school often depends on the possibilities a country or region offers for pupils with special needs. As the child develops, there are decisions to make that are very much based on the individual.
Some children (particularly girls) with Fragile X Syndrome (FXS) can happily continue into secondary education in a regular school. Some will even go to a college or on to a university, or decide for vocational education. Often, males may attend a regular school that can offer support for their needs in order to be able to follow education based on their individual possibilities. For others, a special school might be the better choice.

The important thing is to have a happy child who is settled. There are many possibilities and it is important to discover what they enjoy doing. For parents, it is important to carefully examine what is available in their region and to talk to teachers and school personnel in order to find out where there child will get the best education. Often, teachers never had a child with Fragile X, so it is important to explain to them what is needed in order to optimally support the child.

Further reading:
> Behavior and FXS

How can I help my child transition to independent living as an adult?

It is never too early to start with preparations, but it can easily become too late. As soon as education approaches an endpoint, one should take a look around and do some research about different possibilities. Depending on the country you live in, there will be social programs provided by the government; charities which support those with disability to find work; social enterprises for employment; shared living accommodation; training in independent living and life skills. It is important to find out what is available where you live. Your country's fragile x association can give you guidance on this. Talking to other fragile x families is also useful, as you can get ideas and learn from their experiences.

What issues affect adults with Fragile X Syndrome?

[To be included soon]

What actually is the Fragile X mutation?

Genes are contained in the cell nucleus. They are like recipes for producing proteins or enzymes. Every time a protein is needed, the recipe for it (=gene) is read and the protein is produced inside the cell. Some of the recipe “text” is very important, while other is there for organisational purposes only. Like the headline “Cheesecake” for a cheesecake recipe, there is a little bit of information in a gene that precedes the actual recipe.

In the case of the FMR1 gene, there is a little part inside of that prefix that consists of a certain number of repeating occurrences of recipe text denoted by “CGG”. In the normal case, that number of repetitions of the CGG triplet is about 32 on average. For some still unexplained reasons, it can happen that the number of CGG repeats grows from one generation to the next. Unfortunately, this process can happen again in the next generation, until the sequence length of CGG finally becomes problematic (and the gene is considered being mutated). There are different levels of being “problematic”. The various levels are explained in the next question/answer section.

However, eventually, there can be so many CGG repeats that the gene is considered “dubious” and the gene’s information marked unreadable by the cell. The analogon of a cake recipe: imagine you read to use one pound of yeast in a single cake. You’d be better off not using that recipe, or end up with a real mess in your kitchen!

Further reading:

What is the Fragile X premutation?

The Fragile X genetic mutation happens in different stages. Once the gene starts mutating, the mutation may (or may not) continue and get more severe from one generation to the next (see also above “What actually is the Fragile X mutation” and “How is Fragile X inherited”).

“Getting more severe” means that the CGG triplet repeat number in the gene grows from its average size of approx. 30 first to around 50 (the “grey zone” ranging from 45-54 CGG triplets).

At the end of this continuing mutation process, the CGG repeat size may have reached a number greater than 200, up into the thousands, and the gene will be shut off. The person carrying that gene will develop symptoms of Fragile X Syndrome (FXS).

But even before the gene has reached the full mutation stage (200+ CGGs), that is, between 55 and 200 CGGs, it may have effects on people carrying this so-called Fragile X (or FMR1) “premutation”. There are various conditions associated with the premutation, collected under the term “Fragile X Premutation Associated Conditions” (FXPAC, see next question).

About every 200th female and about every 400th male in the general population carry the FMR1 premutation.

It is important to note that the higher the number of CGG repeats of a woman with the FMR1 premutation is, the more likely it is that her offspring will be born with the FMR1 full mutation, and therefore, develop symptoms of FXS. However, most female carriers of the FMR1 premutation have a lower number of CGG repeats, making it less likely that their children will have FXS.

What is FXPAC?

FXPAC (Fragile X Premutation Associated Conditions) is a term that collects the possible effects of the FMR1 premutation on those who are carriers of the fragile x gene.. The most common conditions affecting carriers of the FMR1 mutation are Fragile X associated primary ovarian insufficiency (FXPOI) and Fragile X associated tremor ataxia syndrome (FXTAS). FXPOI can only affect women, whilst FXTAS is more common and also more severe in (older) men. Both conditions are described in the next sections. Other issues which may affect carriers are:

- Depression
- Anxiety
- Migraines
- Hypothyroidism
- Chronic pain
- Sleep apnea

However, it is believed that in general, premutation carriers are not sicker than individuals in the general population.

The exact influence of the FMR1 premutation is still under investigation. It will need more research to get a clearer view of the symptoms/conditions a premutation carrier may develop.

Further reading:

What is FXPOI?

Fragile X Primary Ovarian Insufficiency (=FXPOI) is a condition in which the ovaries’ function is reduced. It affects about 1 in 4 women carrying the FMR1 premutation. Symptoms can include menstrual irregularities, early menopause (before the age of 40) and infertility.

In particular for family planning, but also for their own health awareness, it is important that women who have been diagnosed with the FMR1 premutation are aware of the fact that they may develop symptoms of FXPOI. Often, diagnoses of the FMR1 premutation are made only after a child was diagnosed with Fragile X Syndrome. However, there are cases where a woman was first diagnosed with FXPOI and only after that, the child was diagnosed with Fragile X Syndrome. Women carrying the full mutation are not affected by FXPOI.

Further reading:

What is FXTAS?

Fragile X associated Tremor/Ataxia Syndrome (FXTAS) is a neurological condition that can occur in both older females and older males carrying the FMR1 premutation. It is more severe and more common in males. Normally, affected people are the grandparents of a child with Fragile X Syndrome.

As the name suggests, major symptoms of FXTAS are intention tremor (trembling/shaking hands), ataxia (balancing problems), cognition issues (short term memory problems, inability to plan things), anxiety and depression. It is sometimes misdiagnosed with Parkinson and/or Alzheimer’s disease.

About 4 out of 10 men over the age of 50 develop symptoms of FXTAS with a variable spectrum and severity of symptoms. Only about every 6th woman with the premutation is affected by FXTAS.

People with the FMR1 full mutation (and therefore, people with Fragile X Syndrome) are not affected by FXTAS.

Further reading:

Why are girls affected differently by Fragile X Syndrome?

Girls have two X chromosomes. In each of their body cells, one X is switched off, and only the other one is responsible for all its biological cell functions. If one of the X chromosomes of a female carries the full mutation of its Fragile X gene, it depends on how many cells have that affected chromosome activated. The fewer cells (in particular the brain cells) which have the Fragile X chromosome activated, the less the girl or woman will be affected by the symptoms of Fragile X Syndrome (FXS). Unfortunately, that often means that the effects of FXS in females are not as easily visible and detectable as in males. Therefore, a diagnosis will often only be reached much later, or even never, causing the affected female to be misunderstood in a lot of situations in life.

What is mosaicism?

Mosaicism in genetics basically means that there can be variations of a gene in one body. In Fragile X Syndrome (FXS), there are two forms of mosaicism, so called size and methylation mosaicism.

Size mosaicism means that there are variations of the level of mutation of the Fragile X gene among the cells (in terms of the length of the CGG repeat number). That means, in some cells, the FMR1 gene is only premutated whereas in others, it is fully mutated.

Methylation mosaicism means that the Fragile X gene is mutated in all cells, but that it is shut off by methylation in some cells and still functioning in others where the gene is unmethylated.

In both cases, the severity of the FXS symptoms may be reduced, depending on how many cells can produce FMR-protein.

Mosaicism is quite common in Fragile X (with size mosaicism occuring more often than methylation mosaicism), leading to a wide spectrum of the severity of symptoms amongst individuals with FXS.

Further reading:

Should I tell my family?

Short answer: Of course! It is almost certain that you will need help and support from your family. And it is important that they understand your child, and that it will have special needs.

Also, Fragile X is a family condition. This means that due to its inheritance pattern, it can occur in various branches of the family tree. So, it might be really important that other family members know that there is something that may have affected their children or be important for future generations and family planning.

Some members of the family, particularly the grandparents (but also some mothers), may develop feelings of guilt, in the sense that they are responsible for forwarding a genetic condition to their offspring. Talk to them, tell them there is zero responsibility for forwarding a genetic condition. Zero.

Having said all of this, in some cases people choose to tell only selected family members and very few friends as they feel their child will be treated badly if the condition is known. This might be more relevant in the case of girls, where discrimination and stigmatisation can occur. Sometimes families prefer to explain that their child has mild learning difficulties, or needs support in some areas. FraXI is working against discrimination and stigmatisation, so that the world is much more accepting of people with Fragile X Syndrome.

How do I tell my child? How do they tell others?

This is a personal decision - some families choose not to tell their Fragile X Syndrome (FXS) child with severe intellectual disability as they would not understand and it might frighten them. However, other parents feel it is best for their child to grow up knowing they have something called Fragile X Syndrome. That it is a part of who they are.

Whether and when you choose to introduce the topic to your child is up to you. They might not ever fully understand the condition, but at least they have a reason for why they might struggle when seeing others around them (e.g. at school) do things more easily. Do talk this issue through with other families who have children with FXS, and seek support and advice from your country organisation.

It is often good for the child to share their condition with their classmates or in a school assembly. This can raise awareness of Fragile X Syndrome, create an understanding of the condition and lead to a more welcoming and inclusive environment at school. This sharing can be supported by a family member (parent or sibling) as appropriate. The important thing is to celebrate each person’s individuality and to promote inclusion and affirmation.

Can I influence if my next child will have Fragile X Syndrome?

Parents of a child that has been diagnosed with Fragile X Syndrome (FXS) may want to have another child and ask themselves if their next child will also have FXS. As FXS is a genetic condition that is a possibility. The chance that the next child will also have Fragile X Syndrome is about 50:50. IMPORTANT: This probability is the same whether or not the previous children have FXS.

It is possible to use medical interventions that are aimed at ensuring a future child does not have FXS. This is an ethically problematic topic. Some parents may feel that avoiding a second child with FXS indicates that they also do not really accept their first child. Other parents may prefer to avoid a future child having FXS, much as they love their affected child. None of the available options that families have in this situation are unproblematic.

In what follows here, a few things must be kept in mind, and you must have understood and accepted these before continuing to read:

  1. Fragile X International was NOT founded to avoid people with Fragile X Syndrome, but rather, to help them and their families. But the topic of this section does of course play a role in the lives of many families, which is why we include it here.
  2. The information given here is not meant to be a substitute for proper family counselling, including genetic counselling and consultation of a medical doctor.
  3. Fragile X International is not responsible for any consequences that reading of the information below may have.
  4. Some of the information given below will need to be balanced with people's religious or ethical beliefs.
If families have a child with FXS, there are various options for family planning:
  1. Decide not to have another child.
  2. Decide to have another child without any interventions/testing.
  3. Do prenatal testing for FXS.
  4. Do preimplantation diagnostics (PGD).
Option 1: This might be a “reasonable” option if the child with FXS is not the first child and has a sibling without FXS. If it is the first child, the desire of parents to have another child without FXS may be strong. Also, all siblings do benefit from each other. Children with FXS may particularly benefit from having a sibling. A lot of families report that their child without FXS benefited from being in the special situation of having a sibling with a disability. That may, however, also put a significant burden on the sibling without FXS. Also, some families with two children with FXS have noticed the co-dependency and special relationship they have with one another, supporting each other in a shared condition.

Option 2: Some families find this unsuitable, as their child with FXS already requires so much attention that they don’t have enough capacity to care for another child that may have FXS. However, in other cases, parents feel they have enough capacity that they don’t find it necessary to consider options 3 or 4; or for moral or ethical reasons wish to have a child regardless of whether the child might have FXS or not.

For both options 3 and 4, it is important to remember that these can only prevent the child from being born with FXS. But there are many thousands of other conditions that can affect humans. So, you cannot guarantee that even if steps are taken to avoid the birth of a child with FXS, that the child will be ”healthy”. This may be a somewhat scary thought, but it is important to keep in mind.

Option 3: Prenatal testing means that a needle will be inserted into the uterus of the pregnant mother to gain a sample of the amniotic fluid that can then be tested to see if the embryo has FXS or not. This process, which is called amniocentesis, is not innocuous, as it may harm or even kill the embryo. So far, there is no non-invasive test for FXS such as the blood sample test for Down Syndrome. The most problematic part is the decision of what to do if there is a positive test for FXS ( which means that the child will most likely (but not 100%) be born having Fragile X Syndrome). Parents should be aware that at that stage, the only way to avoid having a FXS child is to have an abortion.

Some may decide to have the prenatal test in order to be best prepared to welcome their FXS baby, which is a reason to consider testing, even if you are not prepared to have an abortion..It is beyond the scope of this website to discuss all aspects of prenatal testing and abortion. Rather, it requires good genetic, medical and psychological counselling.

Option 4: Preimplantation diagnostics (PGD) means that after an medically assisted conception in a test tube, one cell of the embryo at a very early stage will be taken away from it and tested for FXS. If the test indicates that the embryo has not inherited the Fragile X chromosome, the embryo can be implanted into the uterus and may develop into a child without Fragile X Syndrome. If the test indicates the embryo has FXS then another embryo will be tested. However, this process is complex and can carry physical and psychological burdens.. In many cases, the embryo implantation is unsuccessful in the sense that it does not result in a pregnancy. Also, preimplantation diagnostics is expensive and will normally not be paid by any health insurance, though it is sometimes covered by nationalised health systems.

Both options 3 and 4 are not available in many countries for cultural, ethical, religious or health system related reasons or combinations thereof. As mentioned above, family planning cannot be completely covered by this short summary and needs proper family, genetic, and medical counselling.

Where can I find information on research opportunities?

Ideally, your national Fragile X association will be contacted by researchers who want to do research about Fragile X. Your association would then do some checks to see if safety and ethical requirements are fulfilled. Provided everything looks in order, they would pass the information on to the association’s members. If you get directly contacted by research institutions, you need to make sure yourself that everything is fine. Of course, in many countries, every research project involving patients/vulnerable individuals needs to go through an ethical check process, e.g. by applying at a University’s ethical committee, in order to get confirmation that good ethical principles are met. However, often the time frame for this process is very short and experts in the field will hardly be involved in the ethical committees’ decision process. Your country association can seek advice from FraXI’s Research Committee when considering research opportunities.

Particularly in clinical trials involving new medication candidates, families should be especially careful, as there are several risks involved. Questions like “Have I really understood what is given to my child?”, “Do I really know the possible side effects?”, “Do I really think my child is willing to take part in the trial?” are of great importance and should honestly be considered and answered. In particular, the last question is far from easy to answer, as most people with Fragile X can’t give consent to participate in a medical trial on their own.

What if I’ve heard of a drug that I want to try and I’m not sure it’s safe?

Please consult with your paediatrician or general practitioner, or whoever medical professional is responsible and would prescribe the desired medication. Make sure he/she and in particular, you yourself have completely understood what kind of side effects may occur. Plus, it needs to be kept in mind that people with Fragile X may not be able to report medical problems properly. So the time it takes until the caring persons realises there is a problem that occurred with a medication can be longer than usual, and may have gotten more severe until then. In all cases, medical professionals must be involved when considering a pharmaceutical intervention for a person with Fragile X, and there must be constant supervision.

What are the diagnosis codes for Fragile X and why do they matter?

Fragile X Syndrome is coded in several medical coding systems, among them ICD-10/11 and ORPHA-Code. The particular codes for Fragile X Syndrome are:

ICD-10: Q99.2
ICD-11: LD55
ORPHA-Code: 908

Diseases/conditions are coded, that is, they get a number (code), so that they can easily be identified within a country’s health system. Normally, a paediatrician who receives a genetic diagnosis from a lab, or the geneticist of a hospital that took care of the diagnosis process will write down not only the name of the condition (e.g. “Fragile X Syndrome”), but the identifying code, which would normally be Q99.2 for Fragile X Syndrome. In the future, due to extensions and changes of the coding, it might be that this will change, for instance to the newer code ICD-11, which will result in LD55 for Fragile X Syndrome. Of course, it might be that a person has more than one condition, so the records would get additional entries. For instance, it might be appropriate that a person with Fragile X Syndrome who also shows typical symptoms of autism might get another diagnosis recorded, which in the ICD-10 code could be F84.1 for Atypical Autism.

It is important to have all conditions/diseases recorded in a person’s health records with the appropriate code, as that may have an impact on the possibility of the prescription of therapies and reimbursement of the costs for them.

Some Numbers

The Fragile X full mutation is believed to be appearing in around 1 in 4000 newborns. Fragile X Syndrome in males occurs about as often as the full mutation, that is, 1 in 4000. Fragile X Syndrome in females happens somewhat less, about 1 in 6000 perhaps.

The Fragile X premutation occurs in about 1 in 200 females and 1 in 400 males in the general population.

The average number of cgg repeats in a premutation carrier is about 70.

The likelihood of a premutation extending to a full mutation in the next generation strongly depends on the length of the cgg chain. The average likelihood is about 1/3. However, it is much more likely in the higher cgg repeat range and lower in case of fewer cgg repeat lengths. For instance, if the mother has 100 or more cgg repeats, the likelihood of the child having the full mutation is almost 100%, provided it inherits the affected X chromosome from the mother.

[To be extended.]

Further reading: