Case Report The Association of Pseudohypoparathyroidism Type Ia with Chiari Malformation Type I: A Coincidence or a Common Link? Paria Kashani, 1 Madan Roy, 1 Linda Gillis, 1 Olufemi Ajani, 2 and M. Constantine Samaan 3 1 Department of Pediatrics, McMaster University, Hamilton, ON, Canada 2 Division of Neurosurgery, McMaster Children’s Hospital, Hamilton, ON, Canada 3 Division of Pediatric Endocrinology, McMaster Children’s Hospital, Hamilton, ON, Canada Correspondence should be addressed to M. Constantine Samaan; samaanc@mcmaster.ca Received 23 July 2016; Accepted 25 August 2016 Academic Editor: Mamede de Carvalho Copyright © 2016 Paria Kashani et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A 19-month-old boy was referred for progressive weight gain. His past medical history included congenital hypothyroidism and developmental delay. Physical examination revealed characteristics of Albright Hereditary Osteodystrophy, macrocephaly, and calcinosis cutis. He had hypocalcemia, hyperphosphatemia, and elevated Parathyroid Hormone levels. Genetic testing revealed a known mutation of GNAS gene, confrming the diagnosis of Pseudohypoparathyroidism Type Ia (PHP-Ia) (c.34C>T (p.G1n12X)). He had a normal brain MRI at three months, but developmental delay prompted a repeat MRI that revealed Chiari Malformation Type I (CM-I) with hydrocephalus requiring neurosurgical intervention. Tis was followed by improvement in attaining developmental milestones. Recently, he was diagnosed with growth hormone defciency. Tis case suggests the potential association of CM-I with PHP-Ia. Larger studies are needed to assess whether CM-I with hydrocephalus are common associations with PHP-Ia and to defne potential genetic links between these conditions. We propose a low threshold in performing brain MRI on PHP-1a patients, especially those with persistent developmental delay to rule out CM-I. Early intervention may improve neurodevelopmental outcomes and prevent neurosurgical emergencies. 1. Introduction Pseudohypoparathyroidism Type Ia (PHP-Ia) is the most common form of pseudohypoparathyroidism. It is charac- terized by end organ resistance to several hormones. PHP- Ia is an imprinting defect, with heterozygous loss of func- tion mutation of Guanine nucleotide binding protein, alpha subunit 1 (GNAS1) gene on the maternal allele. Tis defect results in singular expression of paternally inherited GNAS1 allele [1]. Te mutation reduces the G-protein alpha- (Gs-) adenylate cyclase complex signaling and results in reduction of cyclic AMP production. cAMP serves as a second mes- senger in G-protein coupled receptor signaling for several hormones [2]. Te most common hormonal resistance noted in PHP- Ia is Tyroid Stimulating Hormone (TSH) and Parathyroid Hormone (PTH). PHP-Ia can also be associated with a char- acteristic phenotype termed Albright Hereditary Osteodys- trophy (AHO) [3], with round facies, short stature, and brachydactyly. Some of these patients also have growth hor- mone defciency [4]. Intellectual disability is present in 45–75% of patients with PHP-Ia, and it has been proposed that Gs is imprinted in the brain [5, 6]. Obesity is a common feature in PHP-Ia and is associated with reduced resting energy expenditure [7] and reduced lipolysis, which is due to resistance to epinephrine [8]. Chiari type I malformation (CM-I) is characterized by elongation of cerebellar tonsils into the cervical canal via foramen magnum, which can compress the herniated tissue [9]. Symptomatic CM-I is usually associated with cervical syringomyelia and hydrocephalus [10]. Patients with CM-I can present with a spectrum of symptoms including sleep apnea [11], irritability, failure to thrive, and developmental delay [12]. In this report, we present a case of PHP-Ia associated with CM-I in a patient referred for management of obesity Hindawi Publishing Corporation Case Reports in Medicine Volume 2016, Article ID 7645938, 4 pages http://dx.doi.org/10.1155/2016/7645938