Syndromic autism
 | This article may be too technical for most readers to understand. (June 2023) |
Syndromic autism (or syndromic autism spectrum disorders) denotes cases of autism spectrum disorder that are associated with a broader medical condition, generally a syndrome. Cases without such association, which account for the majority of total autism cases, are known as non-syndromic autism (or non-syndromic autism spectrum disorders).
Studying the differences and similarities (e.g. common pathways) between syndromic and non-syndromic cases can provide insights about the pathophysiology of autism and pave the way to new autism therapies.[1][2][3][4]
Syndromic autism
Autism spectrum disorder (ASD) is referred to as syndromic when it is one of the many characteristics associated with a broader medical condition, generally a syndrome.
Syndromic autism represents about 25% of the total ASD cases.[4][5] In most[quantify] cases, its etiology is known.[2][4]
Monogenic disorders are one of the causes of syndromic autism, which in this case are also known as monogenic autism spectrum disorders. They account for about 5% of the total ASD cases.
Certain[which?] syndromic forms of ASD can also have different[compared to?] phenomenology.[clarification needed]
Non-syndromic autism
Non-syndromic autism, also called classic autism or idiopathic autism (as in most cases, the etiology is unknown), represents the majority of total autism cases.
In most[quantify] cases, its cause is polygenic.[citation needed]
Classification
A 2017 study[relevant?] proposed to replace the classification "syndromic"/"non-syndromic" ASD into one based on the genetic etiology of the condition, specifying if the syndromic condition occurs in the context of a "phenotype first" clinically defined syndrome or from a "genotype first" molecularly defined syndrome.[4][clarification needed]
Following the proposal, ASD would be divided into three genetic categories:[4]
Clinically defined
Syndromes recognized by clinicians (depending on their experience), typically confirmed by a targeted genetic testing.
- Chromosomal (e.g.: Down syndrome)
- Syndromes caused by mutations in single genes (e.g.: NF1, TSC, PTEN-associated macrocephaly syndrome, some males with FXS)
- Syndromes caused by CNVs (e.g.: microdeletion 22q11.2 syndrome)
- Teratogens (e.g.: valproate aembryopathy)
Molecularly defined
Syndromes recognized by genome-wide testing, not by hypothesis-driven testing (since clinical recognition is difficult).
- Chromosomal (e.g.: isodicentric 15q)
- ASD-risk genes (e.g.: ADNP, ARIDB1B, ANK2, SCN2A)
- ASD-associated CNVs (e.g.: 16p11.2 deletion/duplication, exonic NRXN1 deletions)
Currently undefined
Currently undefined.[clarification needed]
| Condition | Cause | Chromosome(s) involved (if a mutation) | ASD prevalence (95% CI) | Clinically/Molecularly defined | Other characteristics | Ref. |
|---|---|---|---|---|---|---|
| Fragile X syndrome | Monogenic disorder: FMR1 (encodes FMRP) |
X | 30% (20.0–31.0) [male individuals only] 22% (15.0–30.0) [mixed sex] 14% (13–18) [female individuals only] |
Clinically defined [in some males] | Long/narrow face, macroorchidism, long ears and philtrum, mild to moderate intellectual disability, hyperactivity, intellectual disability (ID), seizures | [1][3][4][6] |
| Rett syndrome | Monogenic disorder: MECP2 |
X | 61.0% (46.0–74.0) [female individuals only] | Clinically defined | Microcephaly, breathing irregularities, language deficits, repetitive/stereotyped hand movements, epilepsy, ID | [1][3][4] |
| MECP2 duplication syndrome | Monogenic disorder: MECP2 |
X | 100% [in a single study composed by 9 male participants] | Clinically defined | Brachycephaly, spasticity, recurrent respiratory infections, gastrointestinal hypermotility, genitourinary abnormalities, epilepsy, ID | [1][4][7] |
| Tuberous sclerosis complex | Monogenic disorder: TSC1 TSC2 |
9 16 |
36.0% (33.0–40.0) | Clinically defined | Benign tumours in multiple organs, epilepsy | [1][3][4] |
| Angelman's syndrome | Monogenic disorder: UBE3A |
15 | 34.0% (24.0–37.0) | Cheerful demeanour, microcephaly, epilepsy, speech deficits, sleep disturbance, epilepsy, ID | [1][3] | |
| Phelan-McDermid Syndrome | Monogenic disorder: SHANK3 |
22 | 84% [in a single study composed by 32 participants] | Molecularly defined | [4][8] | |
| Timothy syndrome | Monogenic disorder: CACNA1C |
12 | 80% [in a single study composed by 17 participants] | Clinically defined | [4][9] | |
| Smith-Lemli-Opitz syndrome | Monogenic disorder: DHCR7 |
11 | 55% [in a single study composed by 33 participants] | [10] | ||
| Neurofibromatosis type I | Monogenic disorder: NF1 |
17 | 18% (9.0–29.0) | Clinically defined | [3][4] | |
| PTEN hamartoma tumor syndrome | Monogenic disorder: PTEN |
10 | 17% (8–27) | Clinically defined | [4][11] | |
| Down syndrome | Chromosomal disorder: trisomy 21 |
21 | 16% (8.0–24.0) | Clinically defined | [3][4] | |
| Cohen's syndrome | Monogenic disorder: VPS13B |
8 | 54% (44.0–64.0) | Clinically defined | [3][4] | |
| Cornelia de Lange syndrome | Polygenic disorder | 43% (32.0–53.0) | Clinically defined | [3][4] | ||
| CHARGE syndrome | Monogenic disorder: CHD7 |
8 | 28% (16–41) | Clinically defined | [4][12][13] | |
| Noonan's syndrome | Polygenic disorder | 15% (7.0–26.0) | [3] | |||
| William's syndrome | Microdeletion syndrome: 7q11.23 |
7 | 12% (6.0–20.0) | [3][14] | ||
| 22q11.2 deletion syndrome | Microdeletion syndrome: 22q11.2 |
22 | 11% (5.0–19.0) | Clinically defined | [3][4] | |
| Fetal Valproate Spectrum Disorder | Teratogen: valproate |
8–15% [in VPA exposed children] | Clinically defined | [4][15][16] |
References
- ^ a b c d e f Benger, Matthew; Kinali, Maria; Mazarakis, Nicholas D. (December 2018). "Autism spectrum disorder: prospects for treatment using gene therapy". Molecular Autism. 9 (1): 39. doi:10.1186/s13229-018-0222-8. PMC 6011246. PMID 29951185.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b Sztainberg, Yehezkel; Zoghbi, Huda Y (November 2016). "Lessons learned from studying syndromic autism spectrum disorders". Nature Neuroscience. 19 (11): 1408–1417. doi:10.1038/nn.4420. PMID 27786181. S2CID 3332899. Retrieved 4 June 2023.
- ^ a b c d e f g h i j k l Richards, Caroline; Jones, Christopher; Groves, Laura; Moss, Jo; Oliver, Chris (October 2015). "Prevalence of autism spectrum disorder phenomenology in genetic disorders: a systematic review and meta-analysis". The Lancet Psychiatry. 2 (10): 909–916. doi:10.1016/S2215-0366(15)00376-4. PMID 26341300. Retrieved 27 May 2023.
- ^ a b c d e f g h i j k l m n o p q r s Fernandez, Bridget A.; Scherer, Stephen W. (31 December 2017). "Syndromic autism spectrum disorders: moving from a clinically defined to a molecularly defined approach". Dialogues in Clinical Neuroscience. 19 (4): 353–371. doi:10.31887/DCNS.2017.19.4/sscherer. PMC 5789213. PMID 29398931.
- ^ Bourgeron, Thomas (September 2015). "From the genetic architecture to synaptic plasticity in autism spectrum disorder". Nature Reviews Neuroscience. 16 (9): 551–563. doi:10.1038/nrn3992. PMID 26289574. S2CID 12742356. Retrieved 8 June 2023.
- ^ Marlborough, M.; Welham, A.; Jones, C.; Reckless, S.; Moss, J. (December 2021). "Autism spectrum disorder in females with fragile X syndrome: a systematic review and meta-analysis of prevalence". Journal of Neurodevelopmental Disorders. 13 (1): 28. doi:10.1186/s11689-021-09362-5. PMC 8299695. PMID 34294028.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Ramocki, Melissa B.; Peters, Sarika U.; Tavyev, Y. Jane; Zhang, Feng; Carvalho, Claudia M. B.; Schaaf, Christian P.; Richman, Ronald; Fang, Ping; Glaze, Daniel G.; Lupski, James R.; Zoghbi, Huda Y. (December 2009). "Autism and other neuropsychiatric symptoms are prevalent in individuals with MeCP2 duplication syndrome". Annals of Neurology. 66 (6): 771–782. doi:10.1002/ana.21715. PMC 2801873. PMID 20035514.
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