The tongue microbiome in autism

This post is a quick discussion of the tongue microbiome in autism

Fig 1 A “The gut microbiota is sampled by M cells that deliver bacteria and viruses across the epithelial layer to underlying immune cells, triggering immune responses or tolerance in the mucosa. The M cell pocket is occupied by a B lymphocyte that directs the maturation of M cell function.””M cells transport microbes across the mucosal barrier and deliver them to immune cells like dendritic cells in a process known as transcytosis [3]. The localization of immune cells beneath T1r3+ taste cells is reminiscent of MALT though true lymphoid tissue is located at the base of the tongue in humans.”
Please review McCluskey’s other articles

Taste neuropathways

On one hand, the tongue microbiome is not different between ASD and NT children. [2] KenHub [3] has is a good learning resource on all things about the neurobiology of how we experience taste. Some of the non -tongue innervations might be use in the future.

1. Heisey EM, McCluskey LP. A possible role for taste receptor cells in surveying the oral microbiome. PLoS Biol. 2023 Jan 13;21(1):e3001953 PMC free article
2. Abdulhaq A, Halboub E, Homeida HE, Kumar Basode V, Ghzwani AH, Zain KA, Baraniya D, Chen T, Al-Hebshi NN. Tongue microbiome in children with autism spectrum disorder. J Oral Microbiol. 2021 Jun 22;13(1):1936434 PMC free article
3. Ken Hub taste bud page

The Gingival Microbiome in Autism

The Olsen and Hicks review

A 2019 review by Ingar Olsen and Steven Hicks proposed a “chicken and egg” relationship between autism and the oral microbiome.[1] These authors came from the Department of Oral Biology, Faculty of Dentistry, University of Oslo, Oslo, Norway; bDepartment of Pediatrics, Penn State College of Medicine, Hershey, PA, USA

This review was searched for key letter combinations like “ging”

• The genera Haemophilus in saliva and Streptococcus in dental plaque were significantly more abundant in ASD whereas Prevotella, Selenomonas, Actinomyces,Porphyromonas and Fusobacterium were reduced.
• In dental plaque, however, six phylotypes including Streptococcus, Actinomyces and Capnocytophaga were positively associated with DMFT/S (decayed, missing or filled teeth or surfaces).
• Oral bacteria may be transferred to the gut. One would think bacteria are more likely to be transferred to the gut than bacteria in the gingiva. Localized ‘chronic’ periodontitis bacterium Porphyromonas gingivalis, a putative causitive agent, causes dysbiosis in the periodontal microbiota. This may lead to microbial dysregulation in the gut since each day 10⁸–10¹⁰ of P. gingivalis can be swallowed

“nerve” was mentioned once in this review as it related to the transfer via the olfactory nerve. A little more was found searching for “glia.”[1]

• Blood vessels, septicemia…Do bacteria from the oral cavity enter the general circulation via venus return to the heart and then the brain? The review did not have much to say about this matter.
• perivascular space in the mouth-brain-axis post. The Olsen and Hicks had almost nothing to say about this region.
• Olfactory tract was mentioned only in Figure1 and trigeminal nerve not at all in this review.
• Circumventricular organs page on Wikipedia has an explosion of authors who seem to place these osmoregulary ogans in the 3rd and 4th ventricles in the interface between the blood and the CSF. Nothing is in PubMed related to CVO and SCFA or TMAO. There are several dozen publications on CVO and LPS. Libretests has a better explanation of these windows of decreased barriers between teh blood and our brains.
• BBB, the blood brain barrier is composed of endothelial cells (rose), smooth muscle like pericytes (purple) and astrocytes. (yellow).

Olsen and Hicks seem convinced that there is a connection between the oral microbiome and neurological functioning in ASD. They seem to stop short of providing a convincing mechanistic understanding, perhaps because we don’t have one yet.

Oral hygiene in autism

Besides oral caries. malocclusion, bruxism, periodontal, and gingival disease are concerns in ASD. [2] TGingivitis, is inflammation of the gums, and a subset of peridontal diseaese, in general the disease of tissues serrounding teeth: the gums. Bruxism is excessive teeth grinding. Malocclusion is the failure of upper and lower to align when chewing. It may be brought on by thumb sucking and abnormal chewing behaviors. Three of the reviews [3-5] cited by the Zerman review [2] stated that there were gum and dental issues with autistic children. Many factors included lack of socialization making routine dental care difficult.

Forty-seven adults with ASD, (25 men, 22 women, mean age 33 years) and of normal intelligence and 69 age- and sex-matched typical controls completed a dental examination and questionnaires on oral health, dental hygiene, dietary habits and previous contacts with dental care. Except for increased number of buccal gingival recessions, the oral health was comparable in adults with ASD and the control group. The group with ASD had less snacking, but also less frequent brushing of teeth in the mornings. The stimulated saliva secretion was lower in the ASD group, regardless of medication. Frequencies of dental care contacts were equal in both groups. The most common reason for missing a dental appointment was forgetfulness in the ASD group.[6]

• The number of patients with buccal gingival recessions was significantly higher in the ASD group compared to the controls, 34/47 (72 %) versus 21/58 (36 %) (p < 0.001).
• Mean number of teeth with buccal gingival recessions was 6.3 ± 6.2 in the ASD group compared to 2.7 ± 4.8 in the control group (p = 0.001).
• Occurrence of calculus was equal in both groups (12/46, 26 % vs. 10/58, 17 %, p = 0.273).
• No association between severity of ASD (reflected by higher AQ scores) and DMFS in the ASD group (p = 0.381).
• The stimulated salivary secretion rate was 1.46 ± 0.72 in the ASD group (n = 43) compared to 2.74 ± 1.49 in the control group (n = 55) (p < 0.001) This was not due to increased use of medications in the adult ASD group.[6]

This article could be mistaken but it is clear that the gingiva is critically important as has been shown with other diseases. This makes sense as it would be easier to maintain a consistent microbiome in the gingiva including via biofilms as compared to the tongue which sloughs off frequently so is more transient and likely influenced by the gingival microbiome.

Circumventricular organs

Circumventricular organs are those regions of our brains that are a window to what’s going on in our circulation, the hypothalamus was a key region in my Med Physiology class. The establishment of tertiary lymphoid tissue may constitute virtual CVO in regions of our brains where they do not belong.