Physical phenotype
Large, protruding ears (both)
Long face (vertical maxillary excess)
High-arched palate (related to the above)
Hyperextensible finger joints
Hyperextensible thumbs (double-jointed)
Flat feet
Soft skin
Postpubescent macroorchidism (large testicles in men after puberty)
Hypotonia (low muscle tone)

Intellectual development
Individuals with FXS may present anywhere on a continuum from learning disabilities in the context of a normal intelligence quotient (IQ) to severe intellectual disability, with an average IQ of 40 in males who have complete silencing of the FMR1 gene. Females, who tend to be less affected, generally have an IQ which is normal or borderline with learning difficulties. The main difficulties in individuals with FXS are with working and short-term memory, executive function, visual memory, visual-spatial relationships, and mathematics, with verbal abilities being relatively unaffected.Data on intellectual development in FXS are limited. However, there is some evidence that standardized IQ decreases over time in the majority of cases, apparently as a result of slowed intellectual development. A longitudinal study looking at pairs of siblings where one child was affected and the other was not found that affected children had an intellectual learning rate which was 55% slower than unaffected children.Individuals with FXS often demonstrated language and communicative problems. This may be related to muscle function of the mouth and frontal-lobe deficits. Autism
Fragile X syndrome co-occurs with autism in many cases and is a suspected genetic cause of the autism in these cases. This finding has resulted in screening for FMR1 mutation to be considered mandatory in children diagnosed with autism.
However, many compounds can be metabolized by phase 2 directly or be excreted without any phase 2 reactions occurring. Phase 1 reaction involves oxidation, reduction, hydrolysis, hydration and many other rare chemical reactions. These processes tend to increase water solubility of the drug and can generate metabolites that are more chemically active and/or potentially toxic. Most of phase 2 reactions take place in  cytosol and involve conjugation with endogenous compounds via transferase enzymes. Phase 1 are typically more suitable for elimination. A group of enzymes located in the endoplasmic reticulum, known as cytochrome P-450, is the most important family of metabolizing enzymes in the liver. Cytochrome P-450 is not a single enzyme, but rather consists of a closely related family of 50 isoforms; six of them metabolize 90% of drugs. There is a tremendous diversity of individual P-450 gene products, and this heterogeneity allows the liver to perform oxidation on a vast array of chemicals (including most drugs) in phase 1. Three important characteristics of the P-450 system have roles in drug-induced toxicity:

1. Genetic diversity:Each of the P-450 proteins is unique and accounts (to some extent) for the variation in drug metabolism between individuals. Genetic variations (polymorphism) in P-450 metabolism should be considered when patients exhibit unusual sensitivity or resistance to drug effects at normal doses. Such polymorphism is also responsible for variable drug response among patients of differing ethnic backgrounds. 2. Change in enzyme activity:Many substances can influence the P-450 enzyme mechanism. Drugs interact with the enzyme family in several ways.