The neurobiology of the Prader-Willi phenotype of fragile X syndrome.
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ABSTRACT:
SUBMITTER: Muzar Z
PROVIDER: S-EPMC5116860 | biostudies-literature | 2016 Nov
REPOSITORIES: biostudies-literature
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The neurobiology of the Prader-Willi phenotype of fragile X syndrome.
Muzar Zukhrofi Z Lozano Reymundo R Kolevzon Alexander A Hagerman Randi J RJ
Intractable & rare diseases research 20161101 4
Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and autism, caused by a CGG expansion to greater than 200 repeats in the promoter region of <i>FMR1</i> on the bottom of the X chromosome. A subgroup of individuals with FXS experience hyperphagia, lack of satiation after meals and severe obesity, this subgroup is referred to have the Prader-Willi phenotype of FXS. Prader-Willi syndrome is one of the most common genetic severe obesity disorders known and it is ...[more]
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Project description:Prader-Willi syndrome (PWS) is a highly variable genetic disorder affecting multiple body systems whose most consistent major manifestations include hypotonia with poor suck and poor weight gain in infancy; mild mental retardation, hypogonadism, growth hormone insufficiency causing short stature for the family, early childhood-onset hyperphagia and obesity, characteristic appearance, and behavioral and sometimes psychiatric disturbance. Many more minor characteristics can be helpful in diagnosis and important in management. PWS is an example of a genetic condition involving genomic imprinting. It can occur by three main mechanisms, which lead to absence of expression of paternally inherited genes in the 15q11.2-q13 region: paternal microdeletion, maternal uniparental disomy, and imprinting defect.
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Project description:Prader-Willi syndrome (PWS) is a complex imprinting disorder related to genomic errors that inactivate paternally-inherited genes on chromosome 15q11-q13 with severe implications on endocrine, cognitive and neurologic systems, metabolism, and behavior. The absence of expression of one or more genes at the PWS critical region contributes to different phenotypes. There are three molecular mechanisms of occurrence: paternal deletion of the 15q11-q13 region; maternal uniparental disomy 15; or imprinting defects. Although there is a clinical diagnostic consensus criteria, DNA methylation status must be confirmed through genetic testing. The endocrine system can be the most affected in PWS, and growth hormone replacement therapy provides improvement in growth, body composition, and behavioral and physical attributes. A key feature of the syndrome is the hypothalamic dysfunction that may be the basis of several endocrine symptoms. Clinical and molecular complexity in PWS enhances the importance of genetic diagnosis in therapeutic definition and genetic counseling. So far, no single gene mutation has been described to contribute to this genetic disorder or related to any exclusive symptoms. Here we proposed to review individually disrupted genes within the PWS critical region and their reported clinical phenotypes related to the syndrome. While genes such as MKRN3, MAGEL2, NDN, or SNORD115 do not address the full spectrum of PWS symptoms and are less likely to have causal implications in PWS major clinical signs, SNORD116 has emerged as a critical, and possibly, a determinant candidate in PWS, in the recent years. Besides that, the understanding of the biology of the PWS SNORD genes is fairly low at the present. These non-coding RNAs exhibit all the hallmarks of RNA methylation guides and can be incorporated into ribonucleoprotein complexes with possible hypothalamic and endocrine functions. Also, DNA conservation between SNORD sequences across placental mammals strongly suggests that they have a functional role as RNA entities on an evolutionary basis. The broad clinical spectrum observed in PWS and the absence of a clear genotype-phenotype specific correlation imply that the numerous genes involved in the syndrome have an additive deleterious effect on different phenotypes when deficiently expressed.
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Project description:BackgroundSchaaf-Yang syndrome (SYS) is a newly recognized imprinting related syndrome, which is caused by a truncating variant in maternally imprinted MAGEL2 located in 15q11-q13. Yet, precise pathomechanism remains to be solved. We sequenced MAGEL2 in patients suspected Prader-Willi syndrome (PWS) to delineate clinical presentation of SYS. We examined 105 patients with clinically suspected PWS but without a specific PWS genetic alteration. Sanger sequencing of the entire MAGEL2 gene and methylation-specific restriction enzyme treatment to detect the parent of origin were performed. Clinical presentation was retrospectively assessed in detail.ResultsTruncating variants in MAGEL2 were detected in six patients (5.7%), including a pair of siblings. All truncating variants in affected patients were on the paternally derived chromosome, while the healthy father of the affected siblings inherited the variant from his mother. Patients with MAGEL2 variants shared several features with PWS, such as neonatal hypotonia, poor suck, and obesity; however, there were also unique features, including arthrogryposis and a failure to acquire meaningful words. Additionally, an episode of neurological deterioration following febrile illness was confirmed in four of the six patients, which caused severe neurological sequalae.ConclusionsSYS can be present in infants suspected with PWS but some unique features, such as arthrogryposis, can help discriminate between the two syndromes. An episode of neurological deterioration following febrile illness should be recognized as an important complication.
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Project description:Prader-Willi Syndrome Microbiota Targeted loci environmental
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Project description:Prader-Willi Syndrome (PWS) is a complex multisystem genetic disorder that shows great variability, with changing clinical features during a patient's life. The syndrome is due to the loss of expression of several genes encoded on the proximal long arm of chromosome 15 (15q11.2-q13). The complex phenotype is most probably caused by a hypothalamic dysfunction that is responsible for hormonal dysfunctions and for absence of the sense of satiety. For this reason a Prader-Willi (PW) child develops hyperphagia during the initial stage of infancy that can lead to obesity and its complications. During infancy many PW child display a range of behavioural problems that become more noticeable in adolescence and adulthood and interfere mostly with quality of life. Early diagnosis of PWS is important for effective long-term management, and a precocious multidisciplinary approach is fundamental to improve quality of life, prevent complications, and prolong life expectancy.
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Project description:The Prader-Willi syndrome (PWS) is a human imprinting disorder resulting from genomic alterations that inactivate imprinted, paternally expressed genes in human chromosome region 15q11-q13. This genetic condition appears to be a contiguous gene syndrome caused by the loss of at least 2 of a number of genes expressed exclusively from the paternal allele, including SNRPN, MKRN3, MAGEL2, NDN and several snoRNAs, but it is not yet well known which specific genes in this region are associated with this syndrome. Prader-Will-Like syndrome (PWLS) share features of the PWS phenotype and the gene functions disrupted in PWLS are likely to lie in genetic pathways that are important for the development of PWS phenotype. However, the genetic basis of these rare disorders differs and the absence of a correct diagnosis may worsen the prognosis of these individuals due to the endocrine-metabolic malfunctioning associated with the PWS. Therefore, clinicians face a challenge in determining when to request the specific molecular test used to identify patients with classical PWS because the signs and symptoms of PWS are common to other syndromes such as PWLS. This review aims to provide an overview of current knowledge relating to the genetics of PWS and PWLS, with an emphasis on identification of patients that may benefit from further investigation and genetic screening.
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