**6. Conclusion**

*Microorganisms*

[90]

**230**

**Country (Year)**

**ASD (GI+/GI**

21


23

Stool

1H NMR

**↑** Isopropanol, p-cresol.

**↓** GABA (associated to ↓

**↓**Phylotypes closely related to *Prevotella copri* ,

*Feacalibacterium prausnitzii and Haemophilus* 

*parainfluenzae*.

*Streptococcus thermophiles)*

spectroscopy

16S rRNA gene

sequencing

*Data presented here include microbial phylotypes or species and/or relevant metabolites pertaining ASD-associated alterations, compared to non-ASD siblings or unrelated healthy controls.*

*ASD, children with autism spectrum disorder; SIB, siblings without ASD; NTC, neuro typical controls; GI+, with gastrointestinal comorbidities; GI−, without gastrointestinal comorbidities, ↑, increased* 

*level(s);* ↓*, decreased level(s); NS, non statistically significant; FISH, fluorescent in situ hybridization; GC, gas chromatography; HPLC, high performance liquid chromtography; SCFA, short-chain fatty* 

*acids; PPA, propionic acid MS, mass spectroscopy; SPME, solid phase microextraction; 5-HIAA: 5-hydoxy-indoleacetic acid; H-NMR, proton nuclear magnetic resonance; GABA, gamma-amino butyric acid.*

**Table 2.** *Studies on gut microbiome in ASD.*

**↓**

USA (2018)

**−)**

**SIB (GI+/GI**

**−)**

**NTC (GI+GI**

**−)**

**Study Group**

**Specimen** 

**Analytical** 

**Changes in fecal microbiome in ASD**

**Refs.**

**method**

**type**

After the complete sequencing of the human genome was achieved, the scientific community began, in the second half of the past decade, the task of mapping the human microbiota, mainly the intestinal microbiota. In parallel, the notion that the ENS interplay with the intestinal microbiota, generating responses in the CNS, through the GBA and HPA axis, has opened an avenue for the study of gastrointestinal, metabolic, and/or neuropsychiatric disorders.

In this landscape, an increasing body of evidence suggests that HIM has a key role in gut and brain development and functionality but also in pathogenesis of mental disorders, including ASD. Studies on ASD have showed that HIM dysbiosis, with altered Bacteroidetes/Firmicutes ratio, presence of detrimental key species, and dysregulation of bacterial metabolite release, appears to correlate with severity of ASD symptoms. In this regard, intervention measures to restore HIM homeostasis are likely promising.

However, the part concerning the microbiota is only one more piece of the puzzle that are ASDs, mainly because the etiology of such disorders remains elusive.
