[10] Aside from intellectual disability, prominent characteristics of the syndrome may include an elongated face, large or protruding ears, flat feet, larger testes (macroorchidism), and low muscle tone.

Behavioral characteristics may include stereotypic movements (e.g., hand-flapping) and atypical social development, particularly shyness, limited eye contact, memory problems, and difficulty with face encoding.

[29] Social anxiety is one of the most common features associated with FXS, with up to 75% of males in one series characterized as having excessive shyness and 50% having panic attacks.

[11][29] Children with fragile X have very short attention spans, are hyperactive, and show hypersensitivity to visual, auditory, tactile, and olfactory stimuli.

Hyperactivity and disruptive behavior peak in the preschool years and then gradually decline with age, although inattentive symptoms are generally lifelong.

[citation needed] Individuals with fragile X-associated tremor/ataxia syndrome (FXTAS) are likely to experience combinations of dementia, mood, and anxiety disorders.

Males with the FMR1 premutation and clinical evidence of FXTAS were found to have increased occurrence of somatization, obsessive–compulsive disorder, interpersonal sensitivity, depression, phobic anxiety, and psychoticism.

[33] In larger study populations the frequency varies between 13% and 18%,[12][33] consistent with a recent survey of caregivers which found that 14% of males and 6% of females experienced seizures.

[citation needed] Individuals who are carriers of premutation alleles are at risk for developing fragile X-associated tremor/ataxia syndrome (FXTAS), a progressive neurodegenerative disease.

Typically, onset of tremor occurs in the sixth decade of life, with subsequent progression to ataxia (loss of coordination) and gradual cognitive decline.

[34] From their 40s onward, males with FXS begin developing progressively more severe problems in performing tasks that require the central executive of working memory.

Women with FXPOI still have the chance to get pregnant in about 10% of cases, because their ovaries occasionally release viable eggs through "escape" ovulation.

[48] Fragile X syndrome has traditionally been considered an X-linked recessive condition with variable expressivity and possibly reduced penetrance.

Due to genetic anticipation and X-inactivation in females, the inheritance of Fragile X syndrome does not follow the usual pattern of X-linked dominant inheritance, and scholars from The University of Chicago Medical Center and Groningen University Hospital have had an abstract published in the American Journal of Medical Genetics that proposes discontinuing labeling X-linked disorders as dominant or recessive.

Before the FMR1 gene was discovered, analysis of pedigrees showed the presence of male carriers who were asymptomatic, with their grandchildren affected by the condition at a higher rate than their siblings suggesting that genetic anticipation was occurring.

[51] The explanation for this phenomenon is that male carriers pass on their premutation to all of their daughters, with the length of the FMR1 CGG repeat typically not increasing during meiosis, the cell division that is required to produce sperm.

Mosaicism can result from instability in the CGG repeats, and affected individuals may show classic symptoms, although some evidence suggests higher intellectual abilities compared to those with a full mutation.

[11][14] It appears to be primarily responsible for selectively binding to around 4% of mRNA in mammalian brains and transporting it out of the cell nucleus and to the synapses of neurons.

The subsequent abnormalities in the formation and function of synapses and development of neural circuits result in impaired neuroplasticity, an integral part of memory and learning.

[11][14][29] The downregulation of GABA pathways, which serve an inhibitory function and are involved in learning and memory, may be a factor in the anxiety symptoms which are commonly seen in FXS.

Diagnostic tests include PCR to analyze the number of CGG repeats, Southern blot analysis, and examination of AGG trinucleotides in the FMR1 gene region.

[citation needed] Prenatal testing with chorionic villus sampling or amniocentesis allows diagnosis of FMR1 mutation while the fetus is in utero and appears to be reliable.

Most parents notice delays in speech and language skills, difficulties in social and emotional domains as well as sensitivity levels in certain situations with their children.

If an individual is diagnosed with FXS, genetic counseling for testing family members at risk for carrying the full mutation or premutation is a critical first-step.

Due to a higher prevalence of FXS in boys, the most commonly used medications are stimulants that target hyperactivity, impulsivity, and attentional problems.

Following antidepressants, antipsychotics such as risperidone and quetiapine are used to treat high rates of self-injurious, aggressive and aberrant behaviors in this population (Bailey Jr et al., 2012).

[61] Alongside pharmacological treatments, environmental influences such as home environment and parental abilities as well as behavioral interventions such as speech therapy, sensory integration, etc.

[60] While metformin may reduce body weight in persons with fragile X syndrome, it is uncertain whether it improves neurological or psychiatric symptoms.

[11] However, the use of stimulants in the fragile X population is associated with a greater frequency of adverse events including increased anxiety, irritability and mood lability.

And, in 1985, Felix F. de la Cruz outlined extensively the physical, psychological, and cytogenetic characteristics of those with the condition in addition to prospects for therapy.