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First Case of Congenital Myeloproliferative Disorder in a Newborn Diagnosed With Noonan Syndrome

Emeline Maisonneuve, Sandra Whalen, Clémence Conté, Bruno Carbonne, Isabelle Guellec

Noonan syndrome (NS) is one of the most common genetic syndromes, but its diagnosis is difficult antenatally because prenatal ultrasound findings are unspecific. Infants with NS are predisposed to developing juvenile myelomonocytic leukaemia (JMML) or myeloproloferative disorders. We report a case of severe polyhydramnios and hydrops fetalis at 32+6 weeks gestation, complicated by preterm labour. Tocolysis, amnioreduction and pleuroamniotic shunt were performed. Fetal blood sampling showed: 1127 monocytes/mm3 and 245 metamyelocytes/mm3. The patient gave birth at 33 weeks and 4 days to a 2780 g male baby. Absolute monocyte count was maximum at 8000/mm3, without blasts in peripheral blood. Study of the PTPN11 gene identified a de novo heterozygous missense mutation. Chemotherapy could not be started due to the severity of the multiple organ failure. The patient died at 2 months old. The prenatal monocytosis >1000/μL is one of the criteria for JMML. We suggest performing a cordocentesis, including white cell blood count in order to search for myelomonocytic disorders, especially in cases of hydropic fetuses and severe pleural effusions, before placing pleuroamniotic shunts. This could help evoking the diagnosis of NS and anticipating the postnatal clinical course.