What is Fragile X Syndrome?
Introduction
Fragile X syndrome constitutes the most common cause of hereditary developmental delay in children. Because the syndrome is due to a single gene being switched off on one of the X chromosomes, girls diagnosed with fragile X usually have milder levels of intellectual difficulties than boys. Behavioural and cognitive difficulties are common in all students with fragile X but are most severe in boys. The syndrome also shares many similarities with autism but also important differences.
Causes
Fragile X syndrome is caused by an abnormal expansion of DNA just above the tip of the X chromosome's long arm, which may be passed from one generation to the next. Fragile X occurs across every culture and is not related to the age of the mother at the time of conception. In 1991, a DNA test for a gene called the Fragile X Mental Retardation – 1 (FMR1) was introduced. The test, which detects fragile X syndrome with a 99% rate of accuracy, is routinely conducted on a blood sample.
How is fragile X inherited?
Fragile X can be inherited from either a mother or father who carries an abnormal copy of the gene on their X chromosome. Typically, carriers of fragile X syndrome are themselves unaffected and experience neither intellectual impairments nor academic challenges. Since the fragile X gene is on the X chromosome, a father cannot pass on any version of the gene to his sons; a father can only pass on a Y chromosome to his male offspring. A father can, however, transmit an X chromosome to his daughter, who will consequently be a carrier of the gene as well. When the fragile X gene (FMR1) is passed on from a mother to her children, the gene may become dramatically altered to the point of being unable to work properly. When this happens, the gene cannot produce enough or any of the protein coded for it. Although the exact function of this protein is not yet fully understood, it is known to be critical to early intellectual and cognitive development.
Main Areas of Difficulty
The most defining characteristics of fragile X are academic and behaviour challenges.
The most salient academic challenges, especially in males, include:
- delayed and/or unusual patterns of speech;
- delayed language acquisition and repetitive (perseverative) speech;
- weak short- and long-term memory for abstract information such as mental mathematical calculations (e.g. 2 x 6), often leading to anxiety around mathematics;
- lack of spatial awareness and visuo-motor coordination, causing many children with fragile X to appear clumsy and awkward;
- difficulty maintaining attention over a long period for tasks that require abstract reasoning, such as math;
- Extreme difficulty performing sequential tasks, such as problem-solving equations;
- The ability to becoming easily distracted in class by sudden noises; movements and routine transitions when attempting to focus on a given task.
The most salient behaviour challenges include:
- Feelings of being overwhelmed by the demands created by social involvement, novel or unexpected situations and changes, even by the common transitions of daily life;
- Attention and hyperactivity problems, the severity of which often contributes to a clinical diagnosis of Attention Deficit Hyperactivity Disorder (ADHD);
- Social avoidance and anxiety;
- Autism-like characteristics.
Autism vs. Fragile X Syndrome
Commonalities
Current research estimates that 15-25% of children who have fragile X are misdiagnosed as having autism due to the disorders’ many overlapping features which include:
- language delays, echolalia and perseverative (repetitive) speech;
- poor eye contact;
- stereotypic movements such as hand-biting and hand-flapping;
- over-sensitivity to environmental stimuli like sudden noises (e.g. sirens or alarms), movements, or changes in routine such as transitions from one classroom activity to another. The anxiety provoked by sensory overload can often lead to hyperarousal which can lead to outbursts of aggression.
Significant Differences
Needless to say, the misdiagnosis of children with fragile X denies them access to syndrome–specific resources and support systems that they would undoubtedly benefit from, particularly in their early school years when early intervention is most effective. The physical features, social, behavioural and academic impairments present in people with fragile X differ from those in people with autism. Recognizing these features is critical in helping clinicians to properly diagnose the syndrome as early as possible so that effective educational and clinical interventions can be implemented from a young age.
Physical Features
Physical features that characterize the condition include an elongated face, large prominent ears and forehead and in males, macroorchidism (enlarged testicles) post-puberty. However, the wide variability in manifestation in both males and females, makes a diagnosis based on physical features alone almost impossible. It is precisely because of their “normal” appearance that many children are not identified as having fragile X until relatively late in their development.
Social Impairments
In contrast to students with autism who often have difficulty relating to others and understanding the concept of emotions and empathy, students with fragile X often express the desire to communicate and socialize with others. However, their relationships can be hindered by initial extreme shyness. Once they begin to feel at ease with social partners, early social relationships can be quite rich and productive for children with fragile X. Secondly, while students with autism are severely impaired in their ability to understand the intentions and beliefs of others, those with fragile X have a greater potential to develop relatively good “theory of mind” skills. “Theory of mind” refers to the ability to understand the beliefs and intentions of others.
Important strengths in children with fragile X syndrome can include:
- Good verbal skills, especially receptive and expressive vocabularies;
- Well-developed skills in verbal labelling and comprehension;
- Strong short- and long-term memory for meaningful information (e.g. stories, objects, names) with a particular ability to tap into a repertoire of acquired knowledge and vocabulary;
- Strong visual memory. Students with fragile X also have good face and emotion recognition skills;
- Ability to focus for long periods of time without experiencing too much distraction or hyper-arousal, especially if an activity is meaningful and non-sequential.