Brain-stem serotonin transporter availability in maternal uniparental disomy and deletion Prader-Willi syndrome

Psychotic illness in people with Prader-Willi syndrome: a systematic review of clinical presentation, course and phenomenology

BACKGROUND

Prader-Willi syndrome (PWS) is a rare and complex neurodevelopmental disorder resulting from absent paternal expression of maternally imprinted genes at chromosomal locus 15q11-13. This absence of expression occurs as a consequence of a deletion on the chromosome 15 of paternal origin (ca. 70%), a chromosome 15 maternal uniparental disomy (mUPD; ca. 25%), or an imprinting centre defect (IC; ca. 1-3%). At birth, individuals with PWS are severely hypotonic and fail to thrive. Hyperphagia and characteristic physical and neuropsychiatric phenotypes become apparent during childhood. The risk for the development of a co-morbid psychotic illness increases during the teenage years, specifically in those with PWS due to the presence of an mUPD. The primary aim of this literature review is to inform clinical practice. To achieve this, we have undertaken a systematic analysis of the clinical research literature on prevalence, presentation, course, characteristics, diagnosis and treatment of psychotic illness in people with PWS. The secondary aim is to identify clinical aspects of psychotic illness in PWS in need of further investigation.

METHODS AND FINDINGS

A systematic literature review on psychosis in PWS was conducted on the databases Web of Knowledge, PubMed and Scopus, using the terms "((Prader-Willi syndrome) OR (Prader Willi Syndrome)) AND ((psychosis) OR (psychotic illness))". All articles written in English and reporting original human research were reviewed. In all but three of the 16 cohort studies in which the genetic types were known, the authors reported higher rates of psychosis in people with PWS resulting from an mUPD, compared to those with the deletion subtype of PWS. When psychosis was present the presentation was psychosis similar regardless of genetic type and was usually characterised by an acute onset of hallucinations and delusions accompanied by confusion, anxiety and motor symptoms.

CONCLUSIONS

The onset of confusion, an affective cyclical pattern with the presence of abnormal mental beliefs and experiences, usually of rapid onset is suggestive of the development of psychotic illness. Phenomenologically, this psychosis in people with PWS is atypical in comparison to schizophrenia and bipolar disorder in the general population. The relationship to psychosis in the general population and the optimum treatments remain uncertain.

Pharmacodynamic Gene Testing in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a rare genetic disorder with a complex neurobehavioral phenotype associated with considerable psychiatric co-morbidity. This clinical case series, for the first time, describes the distribution and frequency of polymorphisms of pharmacodynamic genes (serotonin transporter, serotonin 2A and 2C receptors, catechol-o-methyltransferase, adrenergic receptor 2A, methylene tetrahydrofolate reductase, and human leucocytic antigens) across the two major molecular classes of PWS in a cohort of 33 referred patients who met medical criteria for testing. When results were pooled across PWS genetic subtypes, genotypic and allelic frequencies did not differ from normative population data. However, when the genetic subtype of PWS was examined, there were differences observed across all genes tested that may affect response to psychotropic medication. Due to small sample size, no statistical significance was found, but results suggest that pharmacodynamic gene testing should be considered before initiating pharmacotherapy in PWS. Larger scale studies are warranted.

Multiple methods used for type detection of uniparental disomy in paternity testing

Uniparental disomy (UPD) has attracted more attention recently in paternity testing, though it is an infrequent genetic event. Although short tandem repeat (STR) profiling has been widely used in paternity testing, it is not sufficient to use STR only to judge the genetic relationship, because the existence of UPD will inevitably affect the results of genotyping. Compared with complete UPD, segmental UPD is more difficult to detect because it does not affect all genotypes on the same chromosome. It is necessary to determine the type of UPD with multiple methods because a single method is not sufficient. Therefore, it is advisable to detect UPD in paternity testing with multiple methods. In this study, after autosomal STR profiling was used, we found that there were several gene loci on the same chromosome that did not conform to Mendelian genetic law, thus we highly suspected the existence of UPD and performed X-STR profiling immediately. Then whole-genome single nucleotide polymorphism (SNP) array analysis was performed to identify the type, and the results provided straightforward evidence for distinguishing complete from segmental UPD. Lastly, we used deletion insertion polymorphism (DIP)-SNP SNaPshot assay and Miseq FGx sequencing (for SNP and STR) to determine whether the mutation source is maternal uniparental disomy (mUPD) or paternal uniparental disomy (pUPD). To avoid false exclusion of kinship, it is vital to determine the type of UPD in paternity testing and effective strategies based on multiple methods to detect the type of UPD are provided in this study.

Complete Paternal Uniparental Disomy of Chromosome 2 in an Asian Female Identified by Short Tandem Repeats and Whole Genome Sequencing

Uniparental disomy (UPD) is a rare type of chromosomal aberration that has sometimes been detected in paternity testing. We examined a 3-person family (father, mother, daughter) first by using short tandem repeat markers, which revealed 4 markers, TPOX, D2S1338, D2S1772, and D2S441, on chromosome 2 that were not transmitted in a Mendelian style. We then performed whole genome sequencing (WGS) to determine the range of the UPD. Chromosome 2 in the daughter showed a complete paternal UPD. To the best of our knowledge, this is the 4th case of complete paternal UPD of chromosome 2 with no clinical phenotype. Our study suggests that WGS, when performed to enhance the accuracy and reliability of parentage testing, can provide a powerful method to detect an UPD.