Early-onset Obesity: Unrecognized First Evidence for GNAS Mutations and Methylation Changes

Annette Grüters-Kieslich; Monica Reyes; Amita Sharma; Cem Demirci; Terry J. DeClue; Erwin Lankes; Dov Tiosano; Dirk Schnabel; Harald Jüppner

Disclosures

J Clin Endocrinol Metab. 2017;102(8):2670-2677. 

In This Article

Materials and Methods

Clinical and laboratory data were obtained from routine investigations, which were performed at obesity and endocrine clinics. Genetic testing for PHP1B was performed in the Endocrine Unit at Massachusetts General Hospital, and all the parents provided written informed consent for genetic testing.

Group 1: Patients With Obesity as First Evidence for Sporadic or Autosomal Dominant PHP1B

Five patients had been referred to pediatric endocrine or obesity clinics because of excessive weight gain and hyperphagia, which had been noted by 3 to 12 months of age. One of these patients (patient 2B) developed clinical signs of hypocalcemia at the age of 14.0 years (i.e., >10 years after the first referral because of obesity), which prompted studies, the results of which suggested the diagnosis of PHP1B. PHP1B had been diagnosed in another patient (patient 3B) shortly after birth because of a positive family history.[19] However, the development of obesity was believed to be unrelated to PHP1B, and she was therefore evaluated further in an obesity clinic.

Because of the previous findings, we selected a group of 24 children from a cohort of 102 consecutive patients with earlyonset obesity to search for GNAS methylation abnormalities. These individuals had been followed at a single center (Charité, Berlin, Germany) because of unexplained obesity that was recognized in the first years of life (age, 0.5 to 3.0 years). Their body mass index ranged from21 to 28 kg/m2, and the individual values were all greater than the 97th percentile. Calcium and PTH levels were not determined as a part of the initial diagnostic evaluation for obesity. With the exception of patient 1B, who had symptomatic hypocalcemia and an elevated PTH level when admitted to his local hospital at the age of 11.5 years, none of the children in this obesity cohort had shown abnormal calcium and phosphate levels during the follow-up period (data not shown).

Group 2: Patients With Obesity as First Evidence for PHP1A

In five patients, initially evaluated because of parental concern of early-onset obesity and impaired growth in some, PHP1A was eventually diagnosed because of AHO features and/or because an older sibling was affected by the same disorder. None of these patients had symptomatic hypocalcemia.

Multiplex Ligation-dependent Probe Amplification and Methylation-specific Multiplex Ligation-dependent Probe Amplification

Genomic DNA was isolated from peripheral blood leukocytes using standard methods. The STX16/GNAS locus was analyzed using multiplex ligation-dependent probe amplification (MLPA) and methylation-specific MLPA, as described previously.[32] Biochemical and endocrine measurements were performed at the participating institutions.

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