Transcriptomics of the Prader-Willi syndrome hypothalamus

A Comprehensive Review of Syndromic Forms of Obesity: Genetic Etiology, Clinical Features and Molecular Diagnosis

Syndromic obesity refers to obesity occurring with additional clinical findings, such as intellectual disability/developmental delay, dysmorphic features, and congenital malformations. PURPOSE OF REVIEW: To present a narrative review regarding the genetic etiology, clinical description, and molecular diagnosis of syndromic obesity, which is a rare condition with high phenotypic variability and genetic heterogeneity. The following syndromes are presented in this review: Prader-Willi, Bardet-Biedl, Pseudohypoparathyroidism, Alström, Smith-Magenis, Cohen, Temple, 1p36 deletion, 16p11.2 microdeletion, Kleefstra, SIM1-related, Börjeson-Forssman-Lehmann, WAGRO, Carpenter, MORM, and MYT1L-related syndromes. RECENT FINDINGS: There are three main groups of mechanisms for syndromic obesity: imprinting, transcriptional activity regulation, and cellular cilia function. For molecular diagnostic, methods of genome-wide investigation should be prioritized over sequencing of panels of syndromic obesity genes. In addition, we present novel syndromic conditions that need further delineation, but evidences suggest they have a higher frequency of obesity. The etiology of syndromic obesity tends to be linked to disrupted neurodevelopment (central) and is associated with a diversity of genes and biological pathways. In the genetic investigation of individuals with syndromic obesity, the possibility that the etiology of the syndromic condition is independent of obesity should be considered. The accurate genetic diagnosis impacts medical management, treatment, and prognosis, and allows proper genetic counseling.

AAV-BDNF gene therapy ameliorates a hypothalamic neuroinflammatory signature in the Magel2-null model of Prader-Willi syndrome

Individuals with Prader-Willi syndrome (PWS) exhibit several metabolic and behavioral abnormalities associated with excessive food-seeking activity. PWS is thought to be driven in part by dysfunctional hypothalamic circuitry and blunted responses to peripheral signals of satiety. Previous work described a hypothalamic transcriptomic signature of individuals with PWS. Notably, PWS patients exhibited downregulation of genes involved in neuronal development and an upregulation of neuroinflammatory genes. Deficiencies of brain-derived neurotrophic factor (BDNF) and its receptor were identified as potential drivers of PWS phenotypes. Our group recently applied an adeno-associated viral (AAV)-BDNF gene therapy within a preclinical PWS model, Magel2-null mice, to improve metabolic and behavioral function. While this proof-of-concept project was promising, it remained unclear how AAV-BDNF was influencing the hypothalamic microenvironment and how its therapeutic effect was mediated. To investigate, we hypothalamically injected AAV-BDNF to wild type and Magel2-null mice and performed mRNA sequencing on hypothalamic tissue. Here, we report that (1) Magel2 deficiency is associated with neuroinflammation in the hypothalamus and (2) AAV-BDNF gene therapy reverses this neuroinflammation. These data newly reveal Magel2-null mice as a valid model of PWS-related neuroinflammation and furthermore suggest that AAV-BDNF may modulate obesity-related neuroinflammatory phenotypes through direct or indirect means.

Hypothalamic syndrome

Hypothalamic syndrome (HS) is a rare disorder caused by disease-related and/or treatment-related injury to the hypothalamus, most commonly associated with rare, non-cancerous parasellar masses, such as craniopharyngiomas, germ cell tumours, gliomas, cysts of Rathke's pouch and Langerhans cell histiocytosis, as well as with genetic neurodevelopmental syndromes, such as Prader-Willi syndrome and septo-optic dysplasia. HS is characterized by intractable weight gain associated with severe morbid obesity, multiple endocrine abnormalities and memory impairment, attention deficit and reduced impulse control as well as increased risk of cardiovascular and metabolic disorders. Currently, there is no cure for this condition but treatments for general obesity are often used in patients with HS, including surgery, medication and counselling. However, these are mostly ineffective and no medications that are specifically approved for the treatment of HS are available. Specific challenges in HS are because the syndrome represents an adverse effect of different diseases, and that diagnostic criteria, aetiology, pathogenesis and management of HS are not completely defined.

Prader-Willi syndrome: an update on obesity and endocrine problems

Prader-Willi syndrome (PWS) is a rare complex genetic disorder that results from a lack of expression of the paternally inherited chromosome 15q11-q13. PWS is characterized by hypotonia and feeding difficulty in early infancy and development of morbid obesity aggravated by uncontrolled hyperphagia after childhood and adolescent. Dysmorphic facial features, delayed motor and language development, various degrees of cognitive impairment, and behavioral problems are common in PWS. Without early, intensive nutritional therapy along with behavioral modification, PWS patients develop severe obesity associated with type 2 diabetes, obstructive sleep apnea, right-side heart failure, and other obesity-related metabolic complications. Hypothalamic dysfunction in PWS can lead to several endocrine disorders, including short stature with growth hormone deficiency, hypothyroidism, central adrenal insufficiency, and hypogonadism. In this review, we discuss the natural history of PWS and the mechanisms of hyperphagia and obesity. We also provide an update on obesity treatments and recommendations for screening and monitoring of various endocrine problems that can occur in PWS.