Clinical Application of an Innovative Multiplex-Fluorescent-Labeled STRs Assay for Prader-Willi Syndrome and Angelman Syndrome

A Review of Prader–Willi Syndrome

Prader–Willi Syndrome (PWS, OMIM #176270) is a rare complex genetic disorder due to the loss of expression of paternally derived genes in the PWS critical region on chromosome 15q11-q13. It affects multiple neuroendocrine systems and may present failure to thrive in infancy, but then, hyperphagia and morbid obesity starting in early childhood became the hallmark of this condition. Short stature, hypogonadism, sleep abnormalities, intellectual disability, and behavioral disturbances highlight the main features of this syndrome. There have been a significant number of advances in our understanding of the genetic mechanisms underlying the disease, especially discoveries of MAGEL2, NDN, MKRN3, and SNORD116 genes in the pathophysiology of PWS. However, early diagnosis and difficulty in treating some of the disease’s most disabling features remain challenging. As our understanding of PWS continues to grow, so does the availability of new therapies and management strategies available to clinicians and families.

Possibility of early diagnosis in a fetus affected by Prader‑Willi syndrome with maternal hetero‑UPD15: A lesson to be learned

Prader-Willi syndrome (PWS), a complicated neurodevelopmental disorder arising from errors in genomic imprinting, is characterized by evident hypotonia along with feeding difficulties and the absence of crying in early infancy. Hyperphagia and obesity are not uncommon in patients with PWS, usually accompanied by intellectual disability, cognitive impairment, short stature, small hands and feet, as well as hypogonadism and typical facial features. Due to the severe complications associated with PWS, a thorough understanding of its features and an early diagnosis, preferably in the fetal period, are important for clinical management. According to previous studies, prenatal diagnosis has been confirmed in only a few cases of PWS, using ultrasound, or as an accidental finding by cytogenetic molecular techniques, as no precise fetal phenotype has been defined. In this present study, an infant with PWS arising from maternal heterodisomy of chromosome 15 is described. This is a typical case of missed diagnosis by fetal ultrasound examination, chromosome karyotype analysis and chromosome microarray (CMA) conducted during the pregnancy. To delineate the complex prenatal characteristics of a fetus with PWS, prenatally-diagnosed cases of PWS described in the literature were reviewed. This present study indicated that although prenatal signs are not sufficient for a diagnosis to be confirmed, a comprehensive consideration of these signs is important in leading to a diagnosis of suspected PWS, and thus prompts further prenatal investigations using molecular genetic tools. Furthermore, this present study also suggested that CMA can lead to a missed diagnosis of PWS/Angelman syndrome and other imprinting disorders despite its high value in the detection of copy-number variants in individuals with developmental delay. If clinical signs strongly suggest PWS, other prenatal molecular genetic investigations, including methylation tests and short tandem repeat-based linkage analysis for uniparental disomy, are recommended as an additional tool to aid diagnosis.

Genetic testing for Prader-Willi syndrome and Angelman syndrome in the clinical practice of Guangdong Province, China

Background

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are clinically distinct neurodevelopmental disorders caused by absence of paternally or maternally expressed imprinted genes on chromosome 15q11.2-q13.3 region.

Methods

3331 individuals was recruited from June 2013 to December 2016 under an institutional review board-approved protocol of informed consent. The methylation-specific PCR was employed as a first-tier screening test. The multiplex-fluorescent-labeled STR linkage analysis was carried out to define the underlying genetic mechanisms. The chromosomal microarray analysis was employed to identify chromosomal breakpoints in confirmed cases, and to detect other chromosomal abnormalities in undiagnosed cases. Genetic counseling and recurrence risk assessment were provided to families with affected individuals.

Results

The methylation-specific PCR identified 36 PWS suspected patients and 13 AS suspected patients. UBE3A sequence analysis identified another 1 patient with AS. The STR linkage analysis define the underlying genetic mechanisms. Thirty PWS patients were with paternal deletions on chromosome region 15q11-q13, 5 with isodisomic uniparental disomy and 1 with mixed segmental isodisomic/ heterodisomic uniparental disomy of maternal chromosome 15. Twelve AS patients were with maternal deletions, 1 with isodisomic uniparental disomy and 1 with UBE3A gene mutation. The chromosomal microarray analysis identified chromosomal breakpoints in confirmed cases, and detected chromosomal abnormalities in another 4 patients with clinically overlapped features but tested negative for PWS/AS. Genetic counseling was offered to all families with affected individuals.

Conclusions

Identifying the disorders at early age, establishing the molecular mechanisms, carrying out treatment intervention and close monitoring can significantly improve the prognosis of PWS/AS patients.

Diagnosis and treatment of GH deficiency in Prader-Willi syndrome

Prader-Willi syndrome (PWS) results from under-expression of the paternally-derived chromosomal region 15q11-13. Growth failure is a recognized feature of PWS, and both quantitative and qualitative defects of the GH/IGF-I axis revealing GH deficiency (GHD) have been demonstrated in most children with PWS. In PWS adults, criteria for GHD are biochemically fulfilled in 8-38% of the studied cohorts. Published data support benefits of early institution of GH therapy (GHT) in PWS children, with positive effects on statural growth, body composition, metabolic homeostasis, and neurocognitive function. Like in pediatric PWS, GHT also yields beneficial effects on lean and body fat, exercise capacity, and quality of life of PWS adults. Although GHT has been generally administered safely in PWS children and adults, careful surveillance of risks is mandatory during prolonged GH replacement for all PWS individuals.