RESUMO
Juvenile myelomonocytic leukemia (JMML) is a rare, generally aggressive myeloproliferative neoplasm affecting young children. It is characterized by granulomonocytic expansion, with monocytosis infiltrating peripheral tissues. JMML is initiated by mutations upregulating RAS signaling. Approximately 10% of cases remain without an identified driver event. Exome sequencing of 2 unrelated cases of familial JMML of unknown genetics and analysis of the French JMML cohort identified 11 patients with variants in SH2B3, encoding LNK, a negative regulator of the JAK-STAT pathway. All variants were absent from healthy population databases, and mutation spectrum was consistent with a loss of function of the LNK protein. A stoploss variant was shown to affect both protein synthesis and stability. The other variants were either truncating or missense, the latter affecting the SH2 domain that interacts with activated JAK. Of the 11 patients, 8 from 5 families inherited pathogenic bi-allelic SH2B3 germline variants from their unaffected heterozygous parents. These children represent half of the cases with no identified causal mutation in the French cohort. They displayed typical clinical and hematological JMML features with neonatal onset and marked thrombocytopenia. They were characterized by absence of additional genetic alterations and a hypomethylated DNA profile with fetal characteristics. All patients showed partial or complete spontaneous clinical resolution. However, progression to thrombocythemia and immunity-related pathologies may be of concern later in life. Bi-allelic SH2B3 germline mutations thus define a new condition predisposing to a JMML-like disorder, suggesting that the JAK pathway deregulation is capable of initiating JMML, and opening new therapeutic options.
RESUMO
The thoracic aortic aneurysm corresponds to the dilation of the ascending part of the aorta, which can lead to a dissection (TAAD for Thoracic Aortic Aneurysm and Dissection) or aortic rupture. The etiologies are diverse, but in approximately 20% of cases a genetic origin is found. About thirty genes are reported to be responsible for the development of TAAD. The majority of these genes encode for proteins involved in the extracellular matrix, the contraction of smooth muscle cells or the growth factor TGF-ß signaling pathway. Identifying the pathogenic variant responsible for the aortic disease becomes essential to make a definitive diagnosis, to guide and to personalize the treatment of the patients but also to screen relatives at risk. The availability and access to genetic testing have improved considerably with the development of new sequencing techniques (NGS for Next Generation Sequencing) and the use of gene panels. This review summarizes the main genes associated with TAAD as well as the current diagnostic strategy.
L'anévrisme de l'aorte thoracique correspond à la dilatation de la partie ascendante de l'aorte pouvant aller jusqu'à la dissection (TAAD pour Thoracic Aortic Aneurysm and Dissection), voire la rupture aortique. Les étiologies sont diverses mais dans environ 20 % des cas, l'origine est génétique. Une trentaine de gènes au total ont été rapportés comme étant responsables du développement de TAAD. La majorité de ces gènes codent pour des protéines impliquées dans la matrice extracellulaire, la contraction des cellules musculaires lisses ou la voie de signalisation du facteur de croissance TGF-ß. Identifier le variant pathogène responsable de la maladie aortique permet de poser un diagnostic définitif, d'orienter, voire de personnaliser la prise en charge des patients et permet le dépistage des apparentés à risque. La disponibilité et l'accès aux tests génétiques se sont considérablement améliorés avec le développement de nouvelles techniques de séquençage (NGS pour Next Generation Sequencing) et l'utilisation de panels de gènes. Cette revue résume les principaux gènes associés aux TAAD, ainsi que la stratégie diagnostique actuelle.
