Table 1 The genetic mechanism, estimated prevalence and suggested behavioural phenotypes of the comparison syndrome groups AS and CdLS

Pitt-Hopkins syndrome (PTHS)

Deletion of or variants in the TCF4 gene located at 18q21.2 that encodes transcription factor 4 [5].

Estimated as 1 in 225,000 to 300,000 [5].

ID, speech and language impairment, anxiety, self-injurious behaviour, aggression, repetitive behaviour and ASD [4,5,6,7].

Angelman syndrome (AS)

Deficiency or disruption to the UBE3A gene located on chromosome 15. Approximately 70% of AS cases are caused by de novo maternal deletions at 15q11-q13 [42].

Estimated at 1 in 20,000 in the population [43].

Severe ID, speech, and language impairment, ataxic movement/movement or balance disorder (e.g. hypermotoric behaviour), enhanced laughter/smiling, happy demeanour, short attention spans and aggression [12].

Cornelia de Lange syndrome (CdLS)

Heterozygous mutation of the NIPBL gene, located on chromosome 5p13 (approximately 65% of cases, with further cases being due to mosaicism). Less commonly caused by mutations in SMC3, SMC1A, HDAC8 and RED21 genes (11% of cases) [44].

Estimated between 1 in 10,000 and 1 in 30,000 live births [45].

ID, speech and language delay, self-injurious behaviour, autistic features, repetitive behaviours, aggression and hyperactivity [25, 36, 40, 41, 46].