Browsing by Author "Bicknell, L.S."

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Biallelic variants in DNA2 cause microcephalic primordial dwarfism.
(Wiley-Liss, 2019) Tarnauskaitė, Z.; Bicknell, L.S.; Marsh, J.A.; Murray, J.E.; Parry, D.A.; Logan, C.V.; Bober, M.B.; de Silva, D.C.; Duker, A.L.; Sillence, D.; Wise, C.; Jackson, A.P.; Murina, O.; Reijns, M.A.M.
Microcephalic primordial dwarfism (MPD) is a group of rare single-gene disorders characterised by extreme reduction in brain and body size from early development onwards. Proteins encoded by MPD-associated genes play important roles in fundamental cellular processes, notably genome replication and repair. Here we report identification of four MPD individuals with biallelic variants in DNA2, which encodes an ATP-dependent helicase/nuclease involved in DNA replication and repair. We demonstrate that the two intronic variants (c.1764-38_1764-37ins(53) and c.74+4A>C) found in these individuals substantially impair DNA2 transcript splicing. Additionally we identify a missense variant (c.1963A>G), affecting a residue of the ATP-dependent helicase domain that is highly conserved between humans and yeast, with the resulting substitution (p.Thr655Ala) predicted to directly impact ATP/ADP binding by DNA2. Our findings support pathogenicity of these variants as biallelic hypomorphic mutations, establishing DNA2 as an MPD-disease gene. This article is protected by copyright. All rights reserved.
Mutations in CDC45, encoding an essential component of the Pre-initiation complex, cause Meier-Gorlin syndrome and craniosynostosis
(University of Chicago Press, 2016) Fenwick, A.L.; Kliszczak, M.; Cooper, F.; Murray, J.; Sanchez-Pulido, L.; Twigg, S.R.; Goriely, A.; McGowan, S.J.; Miller, K.A.; Taylor, I.B.; Logan, C.; Bozdogan, S.; Danda, S.; Dixon, J.; Elsayed, S.M.; Elsobky, E.; Gardham, A.; Hoffer, M.J.; Koopmans, M.; McDonald-McGinn, D.M.; Santen, G.W.; Savarirayan, R.; de Silva, D.; Vanakker, O.; Wall, S.A.; Wilson, L.C.; Yuregir, O.O.; Zackai, E.H.; Ponting, C.P.; Jackson, A.P.; Wilkie, A.; Niedzwiedz, W.; Bicknell, L.S.
DNA replication precisely duplicates the genome to ensure stable inheritance of genetic information. Impaired licensing of origins of replication during the G1 phase of the cell cycle has been implicated in Meier-Gorlin syndrome (MGS), a disorder defined by the triad of short stature, microtia, and a/hypoplastic patellae. Biallelic partial loss-of-function mutations in multiple components of the pre-replication complex (preRC; ORC1, ORC4, ORC6, CDT1, or CDC6) as well as de novo stabilizing mutations in the licensing inhibitor, GMNN, cause MGS. Here we report the identification of mutations in CDC45 in 15 affected individuals from 12 families with MGS and/or craniosynostosis. CDC45 encodes a component of both the pre-initiation (preIC) and CMG helicase complexes, required for initiation of DNA replication origin firing and ongoing DNA synthesis during S-phase itself, respectively, and hence is functionally distinct from previously identified MGS-associated genes. The phenotypes of affected individuals range from syndromic coronal craniosynostosis to severe growth restriction, fulfilling diagnostic criteria for Meier-Gorlin syndrome. All mutations identified were biallelic and included synonymous mutations altering splicing of physiological CDC45 transcripts, as well as amino acid substitutions expected to result in partial loss of function. Functionally, mutations reduce levels of full-length transcripts and protein in subject cells, consistent with partial loss of CDC45 function and a predicted limited rate of DNA replication and cell proliferation. Our findings therefore implicate the preIC as an additional protein complex involved in the etiology of MGS and connect the core cellular machinery of genome replication with growth, chondrogenesis, and cranial suture homeostasis.