Supernumerary chromosome 6 marker associated with paternal uniparental isodisomy of chromosome 6 in a patient with a syndromic disorder of insulin secretion.

The association of both uniparental disomy and small supernumerary marker chromosomes is rare. Clinical impact depends on the presence of imprinted genes and/or the unmasking of a recessive mutation of the chromosome involved in the uniparental disomy and the euchromatic content of the sSMC. Here, we report on the second case of a patient harbouring a de novo supernumerary marker chromosome 6 causing partial trisomy 6p12.3p11.1 associated with a paternal uniparental isodisomy of chromosome 6. Our patient presented with intrauterine growth retardation, macroglossia, initial developmental delay and transient neonatal diabetes mellitus followed by a congenital hyperinsulinism. Diabetes and intrauterine growth retardation can be linked to the paternal isodisomy of the imprinted locus on chromosome 6q24 whereas developmental delay is probably due to the small supernumerary marker chromosome. However, the clinical impact of partial trisomy 6p is difficult to address due to a limited number of patients. The careful clinical examination and the molecular characterization of additional patients with trisomy 6p are needed to further predict the phenotype for genetic counselling. Finally, uniparental disomy should be considered when a sSMC involving a chromosome containing imprinted regions is detected, especially in the prenatal setting.