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OBJECTIVEThe authors present population-based epidemiological data for craniosynostosis regarding incidence, age at diagnosis, sex differences, and frequency of syndromic and familial cases.METHODSThe prospective registry of the Norwegian National Unit for Craniofacial Surgery was used to retrieve data on all individuals with craniosynostosis treated between 2003 and 2017. The cohort was divided into three 5-year groups based on year of birth: 2003–2007, 2008–2012, and 2013–2017.RESULTSThe authors identified 386 individuals with craniosynostosis. Of these, 328 (85%) consented to be registered with further information. The incidence increased significantly during the study period and was 5.5 per 10,000 live births (1/1800) in the last 5-year period. The increase was seen almost exclusively in the nonsyndromic group. Syndromic craniosynostosis accounted for 27% of the cases, and the incidence remained stable throughout the three 5-year periods. Both syndromic and nonsyndromic craniosynostosis were highly suture specific. There was a male preponderance (male/female ratio 2:1), and males accounted for 75% of the individuals with midline synostosis. Overall, 9.5% were index individuals in families with more than one affected member; of these, 73% were nonsyndromic cases.CONCLUSIONSThe incidence of craniosynostosis increased during the study period, and the observed incidence is among the highest reported. The authors attribute this to increasing awareness among healthcare professionals. The number of syndromic cases was high, likely due to a broader definition compared to the majority of earlier reports. The study revealed a high number of familial cases in both syndromic and nonsyndromic craniosynostosis, thus highlighting the importance of genetics as an underlying cause of craniosynostosis.

Summary Truncating variants in exons 33 and 34 of the SNF2-related CREBBP activator protein ( SRCAP ) gene cause the neurodevelopmental disorder (NDD) Floating-Harbor syndrome (FLHS), characterized by short stature, speech delay, and facial dysmorphism. Here, we present a cohort of 33 individuals with clinical features distinct from FLHS and truncating (mostly de novo ) SRCAP variants either proximal (n = 28) or distal (n = 5) to the FLHS locus. Detailed clinical characterization of the proximal SRCAP individuals identified shared characteristics: developmental delay with or without intellectual disability, behavioral and psychiatric problems, non-specific facial features, musculoskeletal issues, and hypotonia. Because FLHS is known to be associated with a unique set of DNA methylation (DNAm) changes in blood, a DNAm signature, we investigated whether there was a distinct signature associated with our affected individuals. A machine-learning model, based on the FLHS DNAm signature, negatively classified all our tested subjects. Comparing proximal variants with typically developing controls, we identified a DNAm signature distinct from the FLHS signature. Based on the DNAm and clinical data, we refer to the condition as “non-FLHS SRCAP -related NDD.” All five distal variants classified negatively using the FLHS DNAm model while two classified positively using the proximal model. This suggests divergent pathogenicity of these variants, though clinically the distal group presented with NDD, similar to the proximal SRCAP group. In summary, for SRCAP , there is a clear relationship between variant location, DNAm profile, and clinical phenotype. These results highlight the power of combined epigenetic, molecular, and clinical studies to identify and characterize genotype-epigenotype-phenotype correlations.

We describe a three-generation Norwegian family with a novel X-linked intellectual disability (XLID) syndrome characterized by subtle facial dysmorphism, autism and severe feeding problems. By exome sequencing we detected a rare missense variant (c.1067A4G, p.(Tyr356Cys)) in the RLIM gene, in two affected male second cousins. Sanger sequencing confirmed the presence of the variant in the four affected males (none of whom were siblings) and in three mothers available for testing. The variant was not present in 100 normal Norwegian controls, has not been reported in variant databases and is deleterious according to in silico prediction tools. The clinical phenotype and the variant co-segregate, yielding a LOD score of 3.0 for linkage to the shared region (36.09 Mb), which contains 242 genes. No other shared rare variants on the X chromosome were detected in the two affected exome-sequenced individuals, and all female carriers had an extremely skewed X-chromosome inactivation pattern. RLIM encodes RING zinc finger protein 12 (RNF12), an ubiquitin ligase that is essential for X inactivation in mice and that acts as a co-regulator of a range of transcription factors, particularly those containing a LIM homeodomain. Tyrosine in position 356 in RNF12 is located within a highly conserved domain essential for binding such transcription factors. Expression of RNF12 is widespread during embryogenesis, and is particularly high in the outer layers of the cerebral cortex. Functional studies are needed to prove a definite causal relationship between the variant and the phenotype. Subsequent reports may confirm a role for RLIM variants in patients with XLID.