Klinische Charakterisierung und Ursachenklärung von seltenen kortikalen Fehlbildungen - Mutationen im CRADD-Gen als Ursache einer neuen rezessiven Form von Lissenzephalie
Zusammenfassung der Projektergebnisse
Lissencephaly (LIS, which subsumes the terms agyria and pachygyria, together with subcortical band heterotopia (SBH) comprises a spectrum of malformations of cortical development caused by insufficient neuronal migration that was first described more than a century ago. LIS is an exclusively genetic disorder that demonstrate genetic heterogeneity and can be inherited in autosomal (dominant and recessive) as well as X-link mode. Progress in molecular genetics has led to identification of 16 LIS-associated genes, leaving the existing clinical classification system insufficient to distinguish the increasingly diverse patterns of LIS. Moreover, a systematic analysis of the genotype-phenotype correlation as well as clinical course and outcomes in patients with mutations in different genes has not been performed. During this project we carried out clinical, imaging and molecular characterization in 811 LIS patients. We recognized 21 distinct imaging patterns that are associated with mutations in different genes or gene groups and develop a new severity grading system that correlate imaging pattern with degree of intellectual disability, probability and severity of the epilepsy and probable clinical outcome. Our work gives the first overview of the mutation frequencies in LIS with the four most frequent genes – LIS1, DCX, TUBA1A and DYNC1H1 – accounting for 69%. Several other genes each accounted for approximately 1% of patients. The overall diagnostic yield after testing 16 known genes was 80%. 20% of patients that remained unsolved mostly presented with the rare morphological subtypes of LIS such as “thin” LIS. “Thin” lissencephaly is a novel autosomal recessive subtype characterized by anterior-predominant undulating or wavy pachygyria with shallow but unusually wide sulci (similar to the LIS seen with RELN mutations), mildly thick (5-7 mm) cortex, and no non-cortical malformations. The majority of the “thin” LIS patients unlike patients with other types of LIS had only mild intellectual disability and well controlled non-convulsive seizures. In total we identified 21 individuals with this specific imaging pattern. 6 of them showed a mild or true megalencephaly (head circumference > 2 SD or > 3 SD respectively). The head size of the other 15 patients were either normal or small (N=3). Whole exome and panel sequencing in 21 “thin” LIS patients revealed homozygous mutations in the CRADD gene in all 6 patients with the increased head size. Surprisingly, CRADD (encodes caspase-recruitmentdomain and death domain containing protein) is an activator of caspase-2-mediated apoptosis and does not participate in neuronal migration. We could convincingly demonstrate that human CRADD mutations associated with “thin” LIS abrogate CRADD’s ability to activate caspase-2 and drive neuronal apoptosis. Moreover, we demonstrated that Cradd knockout mice display megalencephaly and seizures without obvious defects in cortical lamination, supporting a role for CRADD/caspase-2 signaling in mammalian brain development. LIS and megalencephaly associated with defective programmed cell death from loss of CRADD function in humans implicates reduced apoptosis as an important pathophysiological mechanism of cortical malformation. Our data suggest that CRADD/caspase-2 signaling is critical for normal gyration of the developing human neocortex and for normal cognitive ability. Taken together, we performed a detailed analysis of the large cohort of patients with LIS and extensively revised an existing clinical classification. Several significant correlations between the imaging patterns and biological pathways allowed us to construct the first LIS classification system based on the underlying molecular mechanisms. Additionally, we describe a novel clinical LIS form – “thin” LIS and characterized underling genetic cause and its molecular pathomechanism. “Thin” LIS associated with the loss of CRADD function is the first malformation of coritical development associated with the defective programmed cell death, implicating reduced apoptosis as a new pathophysiological mechanism of human cortical malformation.
Projektbezogene Publikationen (Auswahl)
- Identification and Characterization of a Novel Constitutional PIK3CA Mutation in a Child Lacking the Typical Segmental Overgrowth of "PIK3CA-Related Overgrowth Spectrum". Hum Mutat. 2016. 3:242-245
Di Donato N, Rump A, Mirzaa GM, Alcantara D, Oliver A, Schrock E, Dobyns WB, O'Driscoll M
(Siehe online unter https://doi.org/10.1002/humu.22933) - Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant. Am J Hum Genet. AJHG Volume 99, Issue 5, 3 November 2016, Pages 1117-1129
Nataliya Di Donato, Ying Y. Jean, A. Murat Maga, Briana D. Krewson, Alison B. Shupp, Maria I. Avrutsky, Achira Roy, Sarah Collins, Carissa Olds, Rebecca A. Willert, Agnieszka M. Czaja, Rachel Johnson, Jessi A. Stover, Steven Gottlieb, Deborah Bartholdi, A
(Siehe online unter https://doi.org/10.1016/j.ajhg.2016.09.010) - Update on the ACTG1-associated Baraitser-Winter cerebrofrontofacial syndrome. Am J Med Genet. 2016
Di Donato N, Kuechler A, Velgano S, Heinritz W, Bodurtha J, Merchant SR, Breningstall G, Ladda R, Sell S, Altmuller J, Bogershausen N, Timms AE, Hackmann K, Schrock E, Collins S, Olds C, Rump A, Dobyns WB
(Siehe online unter https://doi.org/10.1002/ajmg.a.37771)
