Obesity is a complex, heritable trait influenced by the interplay of genetics, epigenetics, metagenomics and the environment. With the increasing access to high precision diagnostic tools for genetic investigations, numerous genes influencing the phenotype have been identified, especially in early onset severe obesity. This review summarizes the current knowledge on the known genetic causes of obesity and the available therapeutic options. Furthermore, we discuss the role and potential mechanism of epigenetic changes that may be involved as mediators of the environmental influences and that may provide future opportunities for intervention.

Genetic and epigenetic causes of obesity.

PWS is a severe neurodevelopmental genetic disorder now usually diagnosed in the neonatal period from hypotonia and feeding difficulties. Our study analyzed the birth incidence and care of infants with early diagnosis. Data were collected on 61 infants with a molecular diagnosis of PWS born in 2012 and 2013 in France. Thirty-eight infants with PWS were born in 2013. The median age at diagnosis was 18 days. Birth incidence calculated for 2013 was 1/21,000 births. No case was diagnosed prenatally, despite 9 amniocenteses, including 4 for polyhydramnios. Five infants had delayed diagnosis, after 3 months of life. For 2 of them, the diagnosis was not suspected at birth and for 3, FISH analysis in the neonatal period was normal, with no further molecular studies. Ninety-three percent of the neonates were hospitalized, and 84% needed nasogastric tube feeding for a median of 38 days. Swallowing assessment was performed for 45%, at a median age of 10 days. Physiotherapy was started for 76% during hospitalization. Eighty percent of those diagnosed within the first 3 months were seen by a pediatric endocrinologist within the first week of life. Our study is the first to assess the birth incidence of PWS in France, at 1/21,000 births. Some prenatal or neonatal cases remain undiagnosed because of unrecognized clinical signs and the inappropriate choice of the initial molecular test. We also underscore the need to optimize neonatal care of infants with PWS.

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Early diagnosis and care is achieved but should be improved in infants with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a complex multisystem disorder due to the absent expression of the paternally active genes in the PWS critical region on chromosome 15 (15q11.2-q13). The syndrome is considered the most common genetic cause of obesity, occurring in 1:10,000-1:30,000 live births. Its main characteristics include neonatal hypotonia, poor feeding, and lack of appetite in infancy, followed by weight gain, lack of satiety, and uncontrolled appetite, frequently after the age of 2-3 years. The clinical picture includes short stature, multiple endocrine abnormalities (hypogonadism, growth hormone/insulin-like growth factor-I axis dysfunction, hypothyroidism, central adrenal insufficiency), dysmorphic features, scoliosis, osteoporosis, mental retardation, and behavioral and psychiatric problems. Subjects with PWS will become severely obese unless their food intake is strictly controlled. Constant and obsessive food seeking behavior can make life very difficult for both the family and caretakers. Prevention of obesity is mandatory in these patients from the first years of life, because once obesity develops it is difficult to maintain the control of food intake. In fact, PWS subjects die prematurely from complications conventionally related to obesity, including diabetes mellitus, metabolic syndrome, sleep apnea, respiratory insufficiency, and cardiovascular disease. The mechanisms underlying hyperphagia in PWS are not completely known, and to date no drugs have proven their efficacy in controlling appetite. Consequently, dietary restriction, physical activity, and behavior management are fundamental in the prevention and management of obesity in PWS. In spite of all available therapeutic tools, however, successful weight loss and maintenance are hardly accomplished. In this context, clinical trials with new drugs have been initiated in order to find new possibilities of a therapy for obesity in these patients. The preliminary results of these studies seem to be encouraging. On the other hand, until well-proven medical treatments are available, bariatric surgery can be taken into consideration, especially in PWS patients with life-threatening comorbidities.

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Obesity management in Prader-Willi syndrome: current perspectives.

Prader-Willi syndrome (PWS) is a complex genetic disorder with implications on the endocrine and neurologic systems, metabolism, and behavior. Early in life, PWS is characterized by hypotonia and failure to thrive, followed by obesity and hyperphagia. Patients with PWS develop hypothalamic dysfunction which may lead growth hormone deficiency (GHD), hypogonadism, hypothyroidism, adrenal insufficiency, and poor bone mineral density (BMD). In addition to hypothalamic dysfunction, individuals with PWS have increased risk for obesity which may be complicated by metabolic syndrome and type 2 diabetes mellitus (T2DM). In this paper, we will review the current literature pertaining to the endocrine concerns of PWS and current recommendations for screening and management of these conditions.

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Review of Prader-Willi syndrome: the endocrine approach

Endocrine disorders in Prader-Willi syndrome: a model to understand and treat hypothalamic dysfunction.

BACKGROUND AND OBJECTIVES: Patients with Prader–Willi syndrome (PWS) display poor feeding and social skills as infants and fewer hypothalamic oxytocin (OXT)-producing neurons were documented in adults. Animal data demonstrated that early treatment with OXT restores sucking after birth. Our aim is to reproduce these data in infants with PWS. METHODS: We conducted a phase 2 escalating dose study of a short course (7 days) of intranasal OXT administration. We enrolled 18 infants with PWS under 6 months old (6 infants in each step) who received 4 IU of OXT either every other day, daily, or twice daily. We investigated the tolerance and the effects on feeding and social skills and changes in circulating ghrelin and brain connectivity by functional MRI. RESULTS: No adverse events were reported. No dose effect was observed. Sucking assessed by the Neonatal Oral-Motor Scale was abnormal in all infants at baseline and normalized in 88% after treatment. The scores of Neonatal Oral-Motor Scale and videofluoroscopy of swallowing significantly decreased from 16 to 9 (P CONCLUSIONS: OXT is well tolerated in infants with PWS and improves feeding and social skills. These results open perspectives for early treatment in neurodevelopment diseases with feeding problems.

https://pediatrics.aappublications.org/content/pediatrics/early/2017/01/16/peds.2016-2976.full.pdf

Jeanne Pourrinet

Papers

The Use of Oxytocin to Improve Feeding and Social Skills in Infants With Prader-Willi Syndrome.