Front Matter

70 What is Autism?

or other contributors to impairment of social interactions. Some maintain that

ASD with and without intellectual disability represent distinct disorders.

However, concrete genetic links have not been established to explain these

distinct phenotypes. Perhaps if we understood more about common and rare

risk loci, we could more accurately predict diagnosis. For example, the combi-

nation of the genetic background of a family and the presence of a high‐risk

variant may contribute to the development of ASD. To understand this better,

individuals with rare variants should be assessed for a broader range of

disorders.

Why Fragile X Syndrome or Tuberous Sclerosis Should Not

Be Included in ASD

Although persons with ASD may also have conditions knows as Fragile X syn-

drome or tuberous sclerosis, these conditions are not forms of ASD. Fragile X

syndrome, which has symptoms that resemble those associated with ASD, is

clearly a genetically caused disorder that passes on intellectual disability from

one generation to the next (Figure 2.2).

An X chromosone

affected by

Fragile X syndrome

CAUSE

Tr inuoleotide repeat

in the FMR-1 gene on

the X chromosone

APPEARANCE

Portion of chromosone

appears fragile and

about to break

2114

Normal

Tr anslocation

carrier 14/21

Tr anslocation

carrier

45

Gamete formation

Gametes

Normal

46

Tr isomy 21

(Down)

46

Monosomic

(lethel)

45

Chromosone number

Figure 2.2 Fragile X syndrome and Down syndrome have genetic etiologies that are

well‐defined and clear. Neither of them have environmental etiologies. Source: Adapted

from: http://epilepsyu.com/blog/researchers‐propose‐new‐explanation‐for‐symptoms‐of‐

fragile‐x‐syndrome/; https://www.pinterest.se/pin/749990144165025587/.