CBL-Mutated Juvenile Myelomonocytic Leukaemia With Loss of Heterozygosity on 11q Detected by Microarray: Not Always Such a Favourable Outcome.

CBL syndrome is caused by a heterozygous germline mutation in the CBL gene. It is a rare RASopathy that shares many clinical features with mild forms of Noonan syndrome. These patients have a higher risk of developing juvenile myelomonocytic leukaemia (JMML) during early childhood. Here we report a case of an 11-month-old infant with JMML and CBL syndrome. It was caused by a heterozygous de novo germline mutation in the CBL gene and acquired biallelic inactivation of the gene through copy-neutral loss of heterozygosity (CN-LOH) in haematological cells. CBL mutation was not found in parents and siblings. CN-LOH was confirmed by single nucleotide polymorphism array. This patient presented with an aggressive clinical course and required an allogeneic stem cell transplant.