Morning melatonin levels in Prader–Willi syndrome

Prader–Willi syndrome (PWS) is a classical genomic imprinting disorder characterized by hypotonia, hypogonadism, hyperphagia, central obesity, short stature, small hands and feet and learning/ behavioral problems due to a paternal deletion of chromosome 15q11–q13 region (about 70% of cases), maternal disomy 15 (UPD) (about 25%), or imprinting defects or translocations involving chromosome 15 (about 5%) [Butler, 1990; Bittel and Butler, 2005; Cassidy and Driscoll, 2009]. Several of these characteristics are consistent with endocrine and/or metabolic abnormalities involving the hypothalamic-pituitary axis. Similarly, findings of daytime drowsiness, obesity, sleep apnea and possibly scoliosis which are frequently seen in PWS may be linked to melatonin production and function [Bartness et al., 2002; Azeddine et al., 2007]. Two earlier studies reported normal melatonin levels in PWS subjects; however, the studies were limited by sample size, children only, and lack of genetic subtype information [Tamarkin et al., 1982; Willig et al., 1986]. Melatonin is secreted by the pineal gland in synchronization to light/dark cycles achieving maximum plasma concentrations of approximately 200 pg/ml at night and lower daytime levels of approximately 10 pg/ml [Cavallo, 1992; de Leersnyder et al., 2001]. Melatonin is produced from tryptophan with serotonin as an intermediate compound while high dietary tryptophan can elevate plasma levels. It can affect the autonomic regulation of the cardiovascular system, regulation of the hypothalamic– pituitary–gonadal axis, circadian rhythms and wake-sleep cycles [Cavallo, 1993; Commentz and Helmke, 1995; Nishiyama et al., 2001]. Melatonin levels are linked to energy expenditure and body mass regulation [Bartness et al., 2002] with obese pubertal males having an overall increase in melatonin production and release [Fideleff et al., 2006]. Because several PWS features could be influenced by melatonin, morning plasma melatonin levels were measured in 53 PWS subjects (25 males and 28 females) with a mean age of 23.6 years (range 10–50 years). All blood samples were drawn in the clinic setting under standard room lighting conditions. About 60% of the blood samples were collected between 7 and 8 AM and the remaining subjects between 8 and 11 AM with an average time of 8 AM. Ninety percent of the subjects were Caucasian. Age, obesity status, gender, genetic subtype, history of daytime drowsiness, sleep apnea, scoliosis, bone density measures, and diabetes status were recorded as well as any use of selective serotonin reuptake inhibitors (SSRIs), insulin and/or growth hormone. All subjects had genetic testing including DNA methylation, cytogenetic analysis with FISH and/or genotyping of informative markers from the 15q11–q13 region to identify the typical deletion type (type I or type II) or maternal disomy (UPD) as previously described [Bittel and Butler, 2005]. No PWS subjects were on thyroid or growth hormone, but four males were on testosterone and 12 were currently on SSRIs. Ten subjects were diabetic and four were on insulin. No PWS individuals were taking melatonin or dietary supplements with tryptophan. Body mass index (BMI) was calculated (kg/m) for each subject and obesity defined as BMI>30 for adults (>18 years) and a BMI>95% using published standards for sex for subjects less than 18 years [Kuczmarski et al., 2000]. Demographic data and melatonin levels are summarized in Table I. Daytime drowsiness and sleep apnea were determined by the use of questionnaire forms and history at the time of enrollment and sleep apnea verified by reviewing medical records including sleep assessment studies. Bone density measurements were determined by dual X-ray absorptiometry (DEXA) scans at the time of blood collection and scoliosis determined by physical examination and inspection of DEXA scans as previously described [Butler et al., 2001]. Fasting plasma morning melatonin levels were determined by a double-antibody radioimmunoassay (RIA) using a melatonin direct RIA kit purchased from ALPCO Diagnostics (Salem, NH)