ASD is a complex clinical condition, adverse to neurological development and associated with an elevated loss of function, affecting close to 1% of the world’s population. Persons affected by ASD display communication deficit, socialization problems and behavioral alterations. The number of affected boys is 4 times greater than the number of affected girls.
Rett Syndrome is considered a relatively rare neurological development disorder, which has been recognized worldwide since the decade of 1980. Affecting mainly women, with a prevalence of 1 out of 10,000, this syndrome is caused by mutations in the gene MECP2, which is localized in the X chromosome. The patients develop normally until about 18 months of age. At that point, progressive neurological abnormalities begin to appear. Neurological manifestations as autistic-like behavior, stereotypy, loss of speech, microcephaly, convulsions and hypotonia are some of the symptoms described in Rett syndrome patients.
CDKL5 deficiency syndrome is a rare genetic disorder first identified in 2004. Primarily associated with girls, it has been seen in boys and includes many of the clinical features of classic Rett syndrome (including developmental problems, loss of language skills, and repeated hand wringing or hand washing movements), and also causes recurrent seizures beginning in infancy. The disorder is caused by mutations in the CDKL5 gene, that stands for cyclin-dependent kinase-like 5, and is located on the X chromosome. The CDKL5 gene provides instructions for making a protein that is essential for normal brain development, by playing a role in regulating the activity of other genes, including the MECP2 gene (of Rett Syndrome).
Fragile X Syndrome is a genetic disease considered the most frequent cause of inherited mental retardation, compromising neurological development. The cause of Fragile X syndrome is the loss of expression of the FMR1 gene, which is located in the X chromosome. Although this loss happens in both genders, it affects boys more frequently. To this date, Fragile X syndrome remains incurable and patients display compromised development, cognitive and learning deficiencies, as well as behavior and physical phenotypes such as stereotypic disorders.
Phelan-McDermid Syndrome (PMD) is a rare disease, which is associated to micro deletions of the chromosome 22, específically in the region containing the SHANK3 gene. This gene is important for synaptic function and has been related to the organizational density of the postsynaptic regions. Patients suffering from Phelan-McDermid display some autistic characteristics such as delay of language development and intellectual deficiencies. Due to its rarity and the lack of proper clinical diagnosis, this syndrome is frequently misdiagnosed and its true incidence is unknown.
Timothy Syndrome is a rare autosomal dominant disease, caused by mutations on the gene. The syndrome is characterized by physical malformations, neurological and developmental defects. It may include elongation of the heartbeat QT interval, arrhythmia and autism-like symptoms.
These two syndromes imply disruption of neurological development, usually associated to Autism. The syndromes are caused by specific deletions on the chromosome 15. Angelman syndrome is due to reduced expression of the UBE3A gene, on the chromosome inherited from the mother. Prader-Willi syndrome is due to the same deletion, but on the chromosome inherited from the father. Both syndromes display similar behavioral and neurological symptoms. On one hand, cognitive and neurological deficiencies, including convulsions, are much stronger on Angelman. On the other hand, behavioral problems are much stronger in Prader-Willi.