Background and objectives: The premature fusion of one or more cranial sutures has been coined as craniosynostosis, a condition, which is commonly associated with a wide spectrum of clinically overlapping phenotypes. Heterozygous gain-of-function mutations frequently found in FGFR2 have been attributed to various forms of craniosynostosis including Apert-, Pfeiffer- and Crouzon syndrome. However, a relatively large subset of these patients remains FGFR2 mutation negative, thus strongly suggesting genetic heterogeneity. We therefore aimed to elucidate the underlying molecular basis of syndromic craniosynostosis in mutation negative patients.
Methods: We performed whole exome sequencing in a patient clinically diagnosed with Crouzon syndrome in whom mutations in known craniosynostosis genes have been previously excluded. Since consanguinity was suspected, variants in regions of homozygosity were prioritized. Shortlisted, causative mutations were re-sequenced and further checked for annotation in over 6000 exomes of the Exome Variant Server (EVS). Direct sequencing of all coding regions of the newly identified candidate gene was then conducted in 12 additional syndromic cases.
Results: We detected a total of three different mutations in the low-density lipoprotein-related protein 2, encoded by LRP2, a gene known to be implicated in Donnai-Barrow syndrome but which has not been associated with the development of craniosynostosis so far. One homozygous splice-site mutation (c.8452 + 1 G/T) in a patient with Crouzon syndrome was located in the LRP domain class A. Another two cases with unclassified syndromic forms of craniosynostosis, carried a homozygous and heterozygous missense substitution (p.R3236Q and p.4019 K) within the LRP domain class B and the calcium-binding EGF-like domain respectively.
Conclusions: In this study, we were able to identify LRP2 as a novel gene underlying syndromic forms of craniosynostosis. Additional functional studies on LRP2 and its downstream molecules will further enhance our understanding on the regulation of cranial suture morphogenesis and fusion.