Gonadotropin-Releasing Hormone Studies to Assess Pubertal Deficiencies in Prader-Willi Syndrome

Research Article

J Pediatri Endocrinol. 2023; 8(1): 1057.

Gonadotropin-Releasing Hormone Studies to Assess Pubertal Deficiencies in Prader-Willi Syndrome

Melissa Kreutz1,2#; Ani Galfayan1,2#; Diane Stafford3*; Manaswitha Khare1,4#; Abhilasha Surampalli1; Brinda Patolia1; June-Anne Gold1,5; Suzanne B Cassidy6; Virginia Kimonis1,7#

1Division of Genetics and Genomic Medicine, Department of Pediatrics, University of California, USA

2Western University of Health Sciences, College of Osteopathic Medicine, USA

3Division of Pediatric Endocrinology, Department of Pediatrics, Stanford University School of Medicine, USA

4Division of Pediatric Hospital Medicine, Department of Pediatrics, Rady Children’s Hospital, USA

5Division of Medical Genetics, Department of Pediatrics, University of Loma Linda, USA

6Division of Medical Genetics, Department of Pediatrics, University of California San Francisco, USA

7Children’s Hospital of Orange County, USA

#These authors have contributed equally to this article.

*Corresponding author: Diane Stafford Division of Pediatric Endocrinology, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA. Email: vkimonis@uci.edu; dejs@stanford.edu

Received: February 22, 2023 Accepted: March 29, 2023 Published: April 05, 2023

Abstract

Patients with Prader-Willi Syndrome (PWS) are known to have variable pubertal development with most having delayed or incomplete puberty. This study aims to evaluate the activity of the Hypothalamic-Pituitary-Gonadal (HPG) axis in individuals with PWS. Thirty-five patients (18 males, 17 females) ages ranging from 3 to 38 years with genetically verified PWS underwent GnRH stimulation testing using gonadorelin along with clinical evaluations. Of patients in the typical age range for initiation of puberty, six had LH peak >5IU/L, indicating activation, but the remaining six had variable peaks, indicating lack of, or indeterminate activation. In some females, physical examination noted breast development to Tanner stage II to III, despite apparent lack of HPG axis activation, while in some males testicular volumes were smaller than expected despite apparent activation of the HPG axis. We studied genotype differences (deletion vs UPD) with respect to HPG axis activation. Mean LH levels were nearly double for PWS females with UPD compared to PWS females with deletion. Both peak LH and peak FSH levels appear to be higher in males with deletion compared to UPD. Inconsistency between physical examination and stimulation testing results and the high variability in the age at activation of the HPG axis accentuates the need for the evaluation of pubertal staging in patients with PWS, and consideration of sex-steroid supplementation.

Keywords: Endocrine; LH; FSH; Deletion; Uniparental disomy

Introduction

Prader-Willi Syndrome (PWS) is a complex, multi-system syndrome that occurs at a frequency of approximately 1/10,000-1/30,000 and is equally distributed among males and females of all ethnic groups [1]. PWS results from loss of expression of paternally inherited genes on the chromosome 15(15q11.2-q13) by a variety of mechanisms which include large deletions (70-75%), maternal uniparental disomy for chromosome 15, UPD15 (20-30%), imprinting defects (2-5%), or rarely balanced translocations [1]. The deletion subtype of parental chromosome 15 is further divided into type I and type II deletions depending on chromosome breakpoint assignments [2]. Some of the patients with UPD 15 have both copies of the two maternal chromosomes 15 (heterodisomy: one copy each from the maternal grand-mother and one from the maternal grand-father), where as others inherit a duplicated single maternal 15(isodisomy). Duplication of deleterious genes in isodisomy could also cause differences between those patients and others with PWS and could point to candidate genes in the region. Clinical diagnosis in infancy and early childhood can be made on the basis of hypotonia with poor suckling in infancy, dysmorphic features including bitemporal narrowing, upslanting palpebral fissures, high palate, small chin, small hands and feet, and gonadal hypoplasia.

PWS is associated with multiple variable endocrine abnormalities, including hypogonadism, central hypothyroidism, Growth Hormone (GH)/insulin-like growth factor I axis dysfunction, and occasional central adrenal insufficiency. These are felt to be due to hypothalamic dysfunction and can result in short stature and delayed pubertal development. The most significant complications of PWS are related to uncontrollable hyperphagia due to hypothalamic dysfunction which results in severe obesity and increased risk of developing type 2 diabetes mellitus if food intake is not controlled externally. This has been reported in 25% of the adult PWS population [3,4]. Decreased lean body mass is common due to the combination of growth hormone deficiency and hypogonadism [1,5-7]. Obesity resulting from PWS in adult patients is distinguishable from exogenous obesity through the dominance of fat mass over lean body mass [6]. Active treatment with GH beginning prior to two years of age has been shown to improve body composition, motor function, cognition, height, and lipid profiles [5,7,8].

While there is a significant variability in the reproductive phenotype of those with PWS, there is commonly dysfunction of the HPG axis that is notable at birth [9]. Individuals with PWS often show clitoral and labia minora hypoplasia in females and a small penis with hypoplastic scrotal sac in males [7]. Also, unilateral or bilateral cryptorchidism is detected in 8090% of males [2]. Further, hypogonadism represents a common finding in adolescence leading to a range of outcomes from normal puberty to stalled puberty to complete or partial pubertal failure due to insufficient secretion of the pituitary gonadotropins LH and FSH and gonadal sex steroids. In adulthood, those with PWS are generally infertile with rare exceptions. Most women have either lack of or irregular menstruation and most men have either undetectable or low testosterone levels [10].

The aim of the current study is to determine the frequency of reproductive dysfunction based on GnRH agonist stimulation testing in a cohort of 35 individuals with PWS, comparing the incidence among the common subtypes, deletion vs UPD, and correlation with physical examination of pubertal status.

Materials and Methods

Subjects: Research protocols were approved by UC Irvine Institutional Review Board, and written informed assents and consents were obtained from all eligible participants or their legally responsible caregivers. Affected subjects aged 3 years to adulthood of both sexes were recruited into the study. Data was collected on 35 individuals with PWS who underwent GnRH stimulation testing to assess for pubertal development as part of a phenotype-genotype correlation study. Participants had a genetically and clinically confirmed diagnosis of PWS by methylation, and FISH and UPD analysis. Individuals who were FISH negative had UPD analysis if parents were available and those who had negative FISH and UPD analysis but were methylation abnormal were presumed to have imprinting center defects and eliminated from analysis because of the small sample size.

Thirty-five individuals with genetically verified PWS underwent GnRH stimulation testing using gonadorelin (2.5ug/kg. up to 100ug). GnRH stimulation testing involves giving a GnRH analog (gonadorelin or leuprolide) to stimulate the pituitary and then monitoring of LH and FSH levels occurred over time. Blood was drawn at baseline, 30 minutes, 60 minutes and 90 minutes post-gonadorelin administration through a standard protocol to measure serum LH and FSH levels at each time interval. If the HPG axis has been activated, there would be an increase in the LH and FSH levels after administration. Lack of rise implies absent activation of the HPG axis [10].

Physical examinations to gather data on breast Tanner staging or testicular volume in all 35 individuals were completed concurrently with the gonadorelin testing. Physical examinations were conducted uniformly by the Same Clinical geneticist (SC).

Data analysis: All data had a normal distribution, based on a p-value>0.05 with Levene’s test for normal distribution. The effect of genetic subtype was tested in pertinent variables of interest between groups using two-tailed, two-sample equal variance t-tests. Statistical significance was based on a p-value of <0.05 for all tests. The results were presented as mean +/-SD.

Results

Thirty-five patients underwent GnRH stimulation testing with gonadorelin. Of these, 18 were male and 17 were female (Table 1). A total of 16 had UPD and 19 had classic 15q deletions. The age range was slightly wider for the female patients with a maximum age of 38 years. All patients below 9 years of age had undetectable LH levels indicating lack of GnRH activation. An LH peak >5IU/L indicates activation of the HPG axis and onset of pubertal development. There was high variability in the group between 9 and 17 years, indicating lack of pubertal development in some patients, and activation of the HPG axis in others. In patients over 18 years, all but one male had an LH peak >5IU/L, indicating activation of the HPG axis in these adults (Table 2 & 3). We did not note precocious puberty in individuals in this cohort.