Etiological investigation of genetic cause in autism spectrum disorder

METHODS: A retrospective descriptive study, with an analytical component, included children and adolescents with autism spectrum disorder followed in consultation at a level 2 hospital, between November 2017 and October 2019. The following variables were analyzed: age, sex, age at the first consultation, family history, objective examination, cognitive assessment, etiological investigation of genetic cause and etiological diagnosis of genetic cause. Statistical analysis was performed using the SPSS®v23 program (significance level 0.05).


INTRODUCTION
The first description of autism spectrum disorder (ASD) was made by Leo Kanner, in 1943 (1) The number of children diagnosed with ASD has increased significantly in recent years (5). The 2017 World Health Organization report shows that, worldwide, 1 in 160 children has ASD (6). Its prevalence is around 1-2%, with a ratio between male gender and female gender of 4-5:1 (7).
Although the etiology of ASD is not yet fully defined, most studies focus on genetic etiology, perhaps because ASD is one of the neurodevelopmental disorders highly heritable. Studies with families and twins suggest that heritability is around 50% (ranging from 26 to 93%) (5). However, only 10-20% of cases have an identified genetic cause (8).
Considering the databases and recently published articles, about 1000 genes are implicated in ASD (9,10). This disorder has been associated with polygenic variants, single nucleotide variants, copy number variations (CNV) and chromosomal abnormalities (10). However, it remains unclear how variations and different genes contribute to the great heterogeneity of the phenotype (11). Each gene represents <1% of the cases and none showed complete specificity for ASD, with several genes involved in multiple neurodevelopmental disorders (12).
In the etiological investigation of ASD, the American College of Medical Genetics and Genomics recommends performing microarray in all cases, molecular study of Fragile X syndrome in boys and specific genetic study in particular cases: This technique allows for the detection of microdeletions and microduplications whose size is too small to be identified by the karyotype, being one of the most used technologies today (7,14).
The aims of this study were to characterize the etiological investigation of cause genetics in ASD performed in patients followed at a level 2 hospital

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and determine the factors that relate to the identification of the etiology of genetic cause in ASD.

METHODS
We carried out a retrospective and descriptive study, with an analytical component.

DISCUSSION
Our study showed a clear predominance of boys in children and adolescents with ASD, with a ratio of 4.6:1, which is in line with what is described in the current literature (2,7,16). Several hypotheses have been suggested to explain this difference between genders, of which the "extreme male brain", the "female protective effect" and the "female autism phenotype" stand out (17).
The "extreme male brain" hypothesis argues that ASD is an extreme expression of physiological and psychological characteristics of the male brain (18), which resulted from exposure to fetal testosterone (19,20). The "female protective effect" theory postulates that girls need a greater mutational load to manifest the ASD phenotype in relation to boys (19). This latter hypothesis is supported by studies that show that girls have an excess of CNV in deletion, mutations that are more harmful to the genes than those found in boys (19), which in our study was not found, in a probable relationship with the small sample number. The "female autism phenotype" is slightly different from the conventional one. For example, girls have less restrictive interests than boys with ASD, which makes the diagnosis difficult (17).
There is yet another factor that potentially contributes to this bias introduced by health professionals, since they associate ASD with the male gender, its sensitivity decreasing in what concerns symptoms in girls (17).
The most prevalent ASD comorbidities in our sample were neurodevelopment disorders, namely GDD and ID, with a combined prevalence of around 50%, a percentage also described in other series (3,5,16).
In our study, the yield of the microarray was 15.6%, slightly higher than what is described in duplication is one of them, being the CNV more regularly described in the studies (10,26), and occurring in 1-3% of children with ASD, usually of maternal inheritance (7,9). In our study, this mutation is present in three siblings with ASD and ID, of maternal heritability. The 1q21.1 region is also frequently associated with ASD in several studies (16,27), including a recognized phenotype, which is manifested by ASD, ID and dysmorphisms. In our sample, we found a case that corresponds to Mutations in the MECP2 gene are responsible for Rett syndrome, which is diagnosed in 1-4% of girls with ASD (7,14). This is in line with that found in our sample, which was 3.7%, corresponding to one girl in the total of girls with ASD followed in consultation. Another syndrome also associated with ASD, which should be excluded in the pre- report that the presence of dysmorphisms, macro or microcephaly, increases the probability of genetic etiology, but such an association was not found in our study (18,29).
ASD is one of the most hereditable neurodevelopment disorders (10), estimated at 51-85%, (25) in agreement with the association found in our study between identification of etiology of genetic cause and the presence of family history of neurodevelopment/neurological pathology.
The limitations of our study are due to the small sample size and its retrospective nature.
Another important limitation was the fact that the etiological investigation of a genetic cause was not carried out uniformly in all children.
It is important to carry out the etiological investigation of ASD in a systematic way in order to adjust surveillance, determine a more reliable prognosis, allow genetic counseling and optimize resources (14). Identifying an etiology for the disorder also provides some emotional relief to the family putting an end to the diagnostic odyssey.
In addition, it is crucial for the establishment of a therapeutic alliance with parents (2). Our stu-

Funding
This study did not receive financial support from external sources

Conflicts of interest disclosure
The authors declare no competing interests relevant to the content of this study.