Findings from a large study comparing deletion and UPD forms of Prader-Willi syndrome were consistent with other evidence in indicating that paternally imprinted genes in the 15q11-13 region constitute a genetic risk factor for aspects of autistic symptomatology. These genes may therefore play a role in the aetiology of autism. By contrast with another report, there was no clear-cut relationship between the size of the deletion and the form of cognitive and behavioural phenotype.

Autism spectrum disorders (ASDs) have been linked with maternally derived duplications/triplications of chromosome 15q11-13 and therefore might occur more frequently in people with Prader-Willi syndrome (PWS) when due to uniparental disomy (UPD), than in other forms of chromosomal abnormality involving this region [i.e. deletion (DEL) forms of PWS and DEL+UPD forms of Angelman's syndrome -(AS)]. Twelve studies regarding ASD in PWS and AS were reviewed. It was noteworthy that among the genetically confirmed UPD and DEL cases of PWS and AS, the rate of ASD was 25.3% (38/150; range 0-36.5%) in PWS and 1.9% in AS (2/104; range 0-100%) (Fisher's exact P<0.0001). Among the subset of cases with confirmed UPD or DEL, the rate of ASD in the UPD cases of PWS was significantly higher (20/53) than in the remaining combined samples (i.e. DEL PWS+UPD AS+DEL AS cases; 20/201) (Fisher's exact P<0.0001). ASD in UPD PWS cases (20/53) compared with DEL PWS cases (18/97) was also statistically significant (Fisher's exact P=0.0176). Thus, the limited available evidence supported the prediction that overexpression of maternally imprinted genes in 15q11-13 confers a risk for ASD. Further research will be required to confirm these findings.

The measures most frequently used to assess psychotic symptoms fail to reflect important dimensions. The Psychotic Symptom Rating Scale (PSYRATS) aims to capture the multidimensional nature of auditory hallucinations and delusions. Individuals (N = 276) who had recently relapsed with positive symptoms completed the auditory hallucinations and delusions PSYRATS scales. These scores were compared with the relevant items from the SAPS and PANSS, and with measures of current mood. Total scores and distribution of items of the PSYRATS scales are presented and correlated with other measures. Positive symptom items from the SAPS and PANSS reflected the more objective aspects of PSYRATS ratings of auditory hallucinations and delusions (frequency and conviction) but were relatively poor at measuring distress. A major strength of the PSYRATS scales is the specific measurement of the distress dimension of symptoms, which is a key target of psychological intervention. It is advised that the PSYRATS should not be used as a total score alone, whilst further research is needed to clarify the best use of potential subscales.

We present clinical data on 33 subjects with additional copies of the Prader-Willi-Angelman critical region (PWACR) contained in a supernumerary marker chromosome (SMC). Twenty-three subjects had a typical large non-mosaic SMC(15) containing two copies of the PWACR. They showed a variable but generally severe phenotype of learning disability and autism, with seizures in approximately two-thirds. The other 10 differed from this typical pattern in respect of mosaicism, variation in copy number, or arrangement of the PWACR within the SMC or number of SMC per cell. Clinical severity increased with the number of additional copies of the PWACR and decreased with mosaicism for a normal cell line. There was a trend for a larger number of seizures to be associated with more severe learning disability. Three subjects with interstitial triplications of 15q11-q13 showed a range of phenotypes similar to those of the typical large SMC(15). All additional copies of the PWACR in this series were maternally-derived. FISH and molecular data localizing the breakpoints of the rearrangements have been previously published or are included in this report. No correlations were found between specific clinical features and variations in breakpoints proximal and distal to the PWACR.

The Prader-Willi/Angelman Critical Region (PWACR; Chromosome 15q11-13) is of interest as a potential locus for genes conferring susceptibility to autism spectrum disorders (ASD). This report describes a female proband referred for evaluation of a possible ASD. Genetic analyses indicated that the proband, her father and one of her sisters, carried a paternally derived interstitial duplication involving 15q11-13. The proband showed evidence of ASD (PDD-NOS), borderline mental retardation, mild hypotonia and joint laxity. Her father and her sister were of normal intelligence and neither was thought to have an ASD, although speech/language difficulties and some autistic type behaviours were reported to have been present early in the development of the sister. This is one of the first reports of a child with a paternal duplication and an autism spectrum disorder. More research is required to determine whether paternally derived duplications that involve 15q11-13 are associated with developmental impairments.