Louie, Raymond J.

Background Pathogenic variants in the zinc finger protein coding genes are rare causes of intellectual disability and congenital malformations. Mutations in the ZNF148 gene causing GDACCF syndrome (global developmental delay, absent or hypoplastic corpus callosum, dysmorphic facies; MIM #617260) have been reported in five individuals so far. Methods As a result of an international collaboration using GeneMatcher Phenome Central Repository and personal communications, here we describe the clinical and molecular genetic characteristics of 22 previously unreported individuals. Results The core clinical phenotype is characterised by developmental delay particularly in the domain of speech development, postnatal growth retardation, microcephaly and facial dysmorphism. Corpus callosum abnormalities appear less frequently than suggested by previous observations. The identified mutations concerned nonsense or frameshift variants that were mainly located in the last exon of the ZNF148 gene. Heterozygous deletion including the entire ZNF148 gene was found in only one case. Most mutations occurred de novo, but were inherited from an affected parent in two families. Conclusion The GDACCF syndrome is clinically diverse, and a genotype-first approach, that is, exome sequencing is recommended for establishing a genetic diagnosis rather than a phenotype-first approach. However, the syndrome may be suspected based on some recurrent, recognisable features. Corpus callosum anomalies were not as constant as previously suggested, we therefore recommend to replace the term ‘GDACCF syndrome’ with ‘ZNF148-related neurodevelopmental disorder’.

Abstract BACKGROUND AND AIMS NEK8/NPHP9 encodes a protein that localizes to the primary cilium. Biallelic NEK8 variants are known to cause multiorgan developmental defects, including kidney cystic dysplasia and extensive extra-renal defects, with heterozygous carrier parents being asymptomatic [1]. This autosomal recessive inheritance is the most common inheritance mode for ciliopathies. Complementary to this, we now propose a dominant negative effect for specific heterozygous NEK8 missense variants in the kinase domain resulting in an autosomal-dominant ciliopathy. METHOD We performed genetic testing in patients from several medical centers. To explore the consequences of the identified NEK8 variants, we are performing cilia staining assays in patients' skin fibroblast and kidney cells, as well as in mIMCD3 cells overexpressing the identified variants. Furthermore, we are examining the impact of the NEK8 variants on replication stress response. RESULTS We identified three distinct heterozygous NEK8 variants in 12 families (Table 1), all leading to missense alterations in the kinase domain. Interestingly the p.Arg45Trp variant is a recurrent variant we detected in 10 unrelated families. All patients have a kidney phenotype that varies from mild focal segmental glomerulosclerosis to prenatal presentation with polycystic kidneys. Most patients have kidney failure needing kidney replacement therapy at varying ages of onset. In all patients, we thoroughly checked whether a second variant could be found. Furthermore, the large symptomatic family and de novo occurrences favor a dominant inheritance mode. Our preliminary results from functional studies show abnormal primary cilia formation in serum-starved cells as well as increased replication stress. CONCLUSION We present the first evidence for a pathogenic effect of heterozygous NEK8 variants. Remarkably our patients present with a kidney limited phenotype as compared to the multiorgan defects found in patients with biallelic variants. This reveals a new mode of inheritance for NEK8 variants and expands genotype-phenotype correlations for this gene.

Background High-impact pathogenic variants in more than a thousand genes are involved in Mendelian forms of neurodevelopmental disorders (NDD). Methods This study describes the molecular and clinical characterisation of 28 probands with NDD harbouring heterozygous AGO1 coding variants, occurring de novo for all those whose transmission could have been verified (26/28). Results A total of 15 unique variants leading to amino acid changes or deletions were identified: 12 missense variants, two in-frame deletions of one codon, and one canonical splice variant leading to a deletion of two amino acid residues. Recurrently identified variants were present in several unrelated individuals: p.(Phe180del), p.(Leu190Pro), p.(Leu190Arg), p.(Gly199Ser), p.(Val254Ile) and p.(Glu376del). AGO1 encodes the Argonaute 1 protein, which functions in gene-silencing pathways mediated by small non-coding RNAs. Three-dimensional protein structure predictions suggest that these variants might alter the flexibility of the AGO1 linker domains, which likely would impair its function in mRNA processing. Affected individuals present with intellectual disability of varying severity, as well as speech and motor delay, autistic behaviour and additional behavioural manifestations. Conclusion Our study establishes that de novo coding variants in AGO1 are involved in a novel monogenic form of NDD, highly similar to the recently reported AGO2 -related NDD.

Germ line mutations in H3F3A and H3F3B cause a previously unidentified neurodevelopmental syndrome.