Genetic-environmental interaction in a unique case of Muenke syndrome with intracranial hypertension.

Abstract

Craniosynostosis, the premature fusion of one of more of the cranial sutures, is relatively common, with an incidence of approximately 1 in 3,000 live births [3]. Although craniosynostosis typically occurs in an isolated manner, without accompanying anomalies, it is also a feature of more than 150 genetic syndromes, the most common of which is Muenke syndrome [4, 15, 19]. Of all patients with craniosynostosis, 8% are estimated to have Muenke syndrome; 24% of patients with craniosynostosis and a known genetic cause have Muenke syndrome [15, 19, 29]. Muenke syndrome is an autosomal dominant craniosynostosis syndrome due to the defining point mutation, c.749C>G, in the FGFR3 gene, resulting in p.Pro250Arg [1, 16]. The condition is characterized by coronal craniosynostosis (bilateral more often than unilateral), carpal and/or tarsal bone fusion, hearing loss, and developmental delay. Following surgical treatment of the craniosynostosis, individuals with Muenke syndrome are five times more likely than individuals with non-syndromic craniosynostosis to need transcranial reoperation for raised intracranial pressure [28]. Vitamin A, which is necessary for the synthesis of visual pigments and is an important component of membrane stability, is obtained from two sources: preformed vitamin A (derived from animal sources) and provitamin A (from carotenoids, fruits, and vegetables) [11, 12]. Preformed vitamin A is efficiently absorbed and used by humans at absorption rates of 70–90%. Provitamin A, derived from carotenoids and plant foods, is absorbed much less efficiently, at rates of 20–30% [12]. Vitamin A toxicity has traditionally been thought of as being unlikely to result from provitamin A due to its relatively poor absorption efficiency and the fact that the conversion of carotenoids to vitamin A is highly regulated. For this reason, carotenemia, a term used to describe excess levels of carotene (a source of provitamin A) in the blood, has been described as being benign aside from the yellow pigmentation of skin. There have been several reports of benign carotenemia secondary to carrot ingestion, the most common cause of carotenemia, as well as dietary dried seaweed, green beans, and nutrient supplementation [14, 17, 26, 27]. The association of vitamin A with intracranial hypertension is well established. In one study of idiopathic intracranial hypertension, affected patients had significant elevation of serum retinal (a derivative of vitamin A) compared to controls [13]. Vitamin A is also one of the known contributors to the pathophysiology of idiopathic intracranial hypertension, although its exact role has yet to be elucidated [8]. Hypervitaminosis A has also been associated with hydrocephalus, a known structural cause of increased intracranial pressure [22].