الفهرس 
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Abstract
ASD is complex neurodevelopmental conditions characterized by language and behavioral problems, social interaction skills impairments, cognitive defects, and communication. The exact ASD etiology is still unknown however, it has been suggested that ASD caused by a combination of factors. There have been many hypotheses for ASD etiology. One of these hypotheses is gut-brain axis abnormalities. The microbial composition of the intestine was proposed to contribute to the development of ASD. The gut microbiota could alter brain function, creating an important link in the bidirectional interactions between nervous system and the intestine. Several studies showed that autistic children with gastrointestinal symptoms show major fecal microbiota alterations. It was reported by several studies that changes in gut microbiota in ASD children could be attributed to yeast infection and leaky gut. Few previous studies have noted an overgrowth of Candida spp. in ASD. Candida could contribute to ASD. Moreover, Ammonia and toxins are metabolic byproducts of Candida which are considered to contribute to autistic symptoms. Propionic acid is in the presence of ammonia metabolites in the GIT, could be converted to beta-alanine, which is structurally comparable to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). (29) and lower absorption of minerals and carbohydrates and high toxin levels are due to excessive growth of yeast in gut. This hypothesis might be useful in understanding the aspect of the biochemical etiology of ASD (30).
The present study aimed to:
1. To study the association of Candida spp. and sensory impairment among children with autism spectrum disorders.
2. To detect the presence of candida spp. in stool of autistic and healthy neuro-typical children.
3. To assess the relation between the presence of candida spp. and ASD symptoms.
4. To detect which candida spp. are most associated with ASD.
This prospective case control study was conducted over a period of one year from August 2019 to July 2020 at Children University Hospital. It included 33 autistic children with age from 4 years to 11 years, who presented to the Autism Clinic of Alexandria University Children’s Hospital. These children were diagnosed with ASDs according to DSM-5 criteria. This study also included a control group of 33 healthy neurotypical unrelated children of similar age and sex, were also included.
Stool specimens were collected from both groups. DNA was extracted from stool samples using ISOLATE Fecal DNA Kit (Bioline, UK) according to the manufacturers’ instructions. The resulting DNA extracts were stored at -80°C until PCR procedures. Candida spp. detection and count was done by SYBR Green Real Time PCR where amplification was performed in a light cycler (Rotor Gene Q, Qiagen, Germany) and SensiFAST TM SYBR No-ROX PCR kit (Bioline Co. UK) was used. The RQ software (Qiagen) plots the rate of change of the relative fluorescence units (RFU) with reference to time (T) (-d (RFU)/dT) on the y axis versus the temperature on the x axis, with the curve peaking at the melting temperature (Tm), and melting curve analysis was always done to check the specificity of the amplification. The copy number of target DNA of each fungal species in each μl of crude DNA template was determined by comparison with the standard curve.
The results of the present study revealed that:
1. There was no statistically significant difference between ASD group and control group in the number of positive cases of candida spp. or in the number of copies of the positive cases.
2. There is a relation between the Candida spp. positive cases and the definite cases of ASD according to SSP score, and this relation was found to be statistically significant.
3. The most candida spp. associated with ASD was C. albicans as it represented (42.2%) of positive cases and this result was found to be statistically significant.
4. There is a relation between the C. albicans positive cases and the definite cases of ASD according to SSP score, and this relation was found to be statistically significant.
5. There is a relation between the C. albicans positive cases and the severity of ASD according to CARS score, and this relation was found to be statistically significant.
It can be concluded from the present study that:
1. The presence of C. albicans increased both the severity and the sensory impairment in ASD cases, and that was found to be statistically significant.
2. There was no statistically significant difference between ASD group and control group in the number of positive cases of Candida spp. or in the number of copies of the positive cases.
from the results of the present study, the following recommendations are suggested:
1. Further studies are recommended to identify the cause why C. albicans was found to increase the severity of ASD.
2. Identify whether it is beneficial to give antifungal therapy for patients with ASD.