| 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, hyperactivity, mild to moderate intellectual disability (ID), seizures | [1][3][4][10] |
| 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][11] |
| 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, 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][12] |
| KCNH1-related disorders |
Monogenic disorder: KCNH1 |
1 |
|
Molecularly defined, formerly clinically defined as Temple–Baraitser Syndrome or Zimmermann–Laband Syndrome |
Mild to severe developmental delay, profound intellectual disability, neonatal hypotonia, myopathic facial appearance, and infantile-onset seizures |
[13] |
| Timothy syndrome | Monogenic disorder:
CACNA1C | 12 | 80% [in a single study composed by 17 participants] | Clinically defined | | [4][14] |
| Smith-Lemli-Opitz syndrome | Monogenic disorder:
DHCR7 | 11 | 55% [in a single study composed by 33 participants] | | | [15] |
| 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][16] |
| 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][17][18] |
| Noonan's syndrome | Polygenic disorder | | 15% (7.0–26.0) | | | [3] |
| Williams syndrome | Microdeletion syndrome:
7q11.23 | 7 | 12% (6.0–20.0) | | | [3][19] |
| 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][20][21] |
