PHEX mutation positive X-linked hypophosphatemic rickets presenting with bilateral proptosis and misdiagnosed as bilateral optic glioma

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 199-237-Disorders of Parathyroid Hormone & Calcium Homeostasis
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-214
Sarar Mohamed*1, Nasir Al-Juryyan2, Rana Hasanato2, Amir Babiker2, Hessah Al-Otaibi3, Amal Al-Hakami2 and Abdelrahman Al-Nemri2
1King Saud University, Riyadh 11461, Saudi Arabi, Saudi Arabia, 2King Saud University,
PHEX mutation positive X-linked hypophosphatemic rickets presenting with bilateral proptosis and misdiagnosed as bilateral optic glioma
Sarar Mohamed1, Nasir Al-Juryyan1,  Rana Hasanato2, Amir Babiker1, Hessah Al-Otaibi1, Amel Hakmi1, Abdelrahman Al-Nemri1
1Department of Pediatrics, College of Medicine, King Saud University
2Department of Pathology, College of Medicine, King Saud University
X-linked hypophosphatemic rickets (XLHR) is a rare form of hereditary rickets. The gene responsible for XLHR was identified on chromosome Xp22.1 and named PHEX (Phosphate regulating Endopeptidase on the X chromosome). XLHR usually presents with short stature, abnormal gait and skeletal manifestations of rickets. We here report on an unusual case of XLHR presented with bilateral proptosis and misdiagnosed as bilateral optic glioma.
Case Report
A 5 year old girl presented to the endocrine clinic with a leg bowing noticed at the age of 1 year and a progressive eye protrusion started at 3 years of age. No history of headaches, visual impairment or symptoms suggestive of hyperthyroidism. She passed through normal development apart from mild delay of motor milestones. She received multiple courses of vitamin D3 without improvement. MRI of brain, done in the referring hospital reported bilateral optic nerve sheath ectasia and bilateral glioma. Clinical examination in our clinic confirms bilateral moderate proptosis in the right eye more than the left with intact visual acuity and eye movements. No lid lag or lid retraction was observed. Fundoscopy showed a pale optic disc. There were no signs  suggestive of hyperthyroidism. Height and weight were at 10th centile. No skeletal signs of rickets observed apart from bowing of legs and waddling gait. Laboratory investigations showed normal serum corrected calcium of 2.3 mmol/l (N= 2.1-2.55), low phosphorus 0.84 mmol/l (N= 0.87-1.45) and ALP of, 486 U/L (N= 50-136). PTH, 25 hydroxyvitamin D, 1, 25 dihydroxyVitamin D, TSH and T4 were normal. Skeletal survey showed generalized osteopenia with no specific signs of rickets.
Molecular genetic analysis of PHEX gene Shows heterozygous mutation c.1735G>A (p.Gly579Arg) which confirms XLHR. The patient was commenced on high dose of alfacalcidol and oral phosphate. Review of the MRI brain confirms presence of bilateral optic nerve sheath ectasia that mimics optic glioma. 
Clinical Lesson
This report highlights the rare association of bilateral proptosis and XLHR secondary to bilateral optic nerve sheath ectasia. This report elucidates the importance of considering XLHR as one of the differential diagnosis of any patient presenting with unexplained bilateral proptosis.

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