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Ferrari L, Mangano E, Bonati MT, Monterosso I, Capitanio D, Chiappori F, Brambilla I, Gelfi C, Battaglia C, Bordoni R, Riva P. Digenic inheritance of subclinical variants in Noonan Syndrome patients: an alternative pathogenic model? Eur J Hum Genet 2020; 28:1432-1445. [PMID: 32514133 PMCID: PMC7608271 DOI: 10.1038/s41431-020-0658-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 04/21/2020] [Accepted: 05/22/2020] [Indexed: 11/22/2022] Open
Abstract
Noonan syndrome (NS) is an autosomal-dominant disorder with variable expressivity and locus heterogeneity. Despite several RAS pathway genes were implicated in NS, 20–30% of patients remain without molecular diagnosis, suggesting the involvement of further genes or multiple mechanisms. Eight patients out of 60, negative for conventional NS mutation analysis, with heterogeneous NS phenotype were investigated by means of target resequencing of 26 RAS/MAPK pathway genes. A trio was further characterized by means of whole-exome sequencing. Protein modeling and in silico prediction of protein stability allowed to identify possible pathogenic RAS pathway variants in four NS patients. A new c.355T>C variant in LZTR1 was found in patient 43. Two patients co-inherited variants in LRP1 and LZTR1 (patient 53), or LRP1 and SOS1 genes (patient 67). The forth patient (56) carried a compound heterozygote of RASAL3 gene variants and also an A2ML1 variant. While these subclinical variants are singularly present in healthy parents, they co-segregate in patients, suggesting their addictive effect and supporting a digenic inheritance, as alternative model to a more common monogenic transmission. The ERK1/2 and SAPK/JNK activation state, assessed on immortalized lymphocytes from patients 53 and 67 showed highest phosphorylation levels compared to their asymptomatic parents. These findings together with the lack of their co-occurrence in the 1000Genomes database strengthen the hypothesis of digenic inheritance in a subset of NS patients. This study suggests caution in the exclusion of subclinical variants that might play a pathogenic role providing new insights for alternative hereditary mechanisms.
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Affiliation(s)
- Luca Ferrari
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale (BIOMETRA), Università degli Studi di Milano, Segrate, Italy
| | - Eleonora Mangano
- Istituto di Tecnologie Biomediche (ITB) Centro Nazionale delle Ricerche (CNR), ITB-CNR, Segrate, Milano, Italy
| | - Maria Teresa Bonati
- Ambulatorio di Genetica Medica, IRCCS Istituto Auxologico Italiano, Milano, Italy.
| | - Ilaria Monterosso
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale (BIOMETRA), Università degli Studi di Milano, Segrate, Italy
| | - Daniele Capitanio
- Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, Milano, Italy.,IRCCS Istituto Ortopedico Galeazzi, Milano, Italy
| | - Federica Chiappori
- Istituto di Tecnologie Biomediche (ITB) Centro Nazionale delle Ricerche (CNR), ITB-CNR, Segrate, Milano, Italy
| | | | - Cecilia Gelfi
- Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, Milano, Italy.,IRCCS Istituto Ortopedico Galeazzi, Milano, Italy
| | - Cristina Battaglia
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale (BIOMETRA), Università degli Studi di Milano, Segrate, Italy.,Istituto di Tecnologie Biomediche (ITB) Centro Nazionale delle Ricerche (CNR), ITB-CNR, Segrate, Milano, Italy
| | - Roberta Bordoni
- Istituto di Tecnologie Biomediche (ITB) Centro Nazionale delle Ricerche (CNR), ITB-CNR, Segrate, Milano, Italy
| | - Paola Riva
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale (BIOMETRA), Università degli Studi di Milano, Segrate, Italy.
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