Mosaic Turner syndrome and hyperinsulinaemic hypoglycaemia

Background. A common and well recognised feature of Turner's syndrome (partial or total monosomy X) is impaired glucose tolerance or type 2 diabetes mellitus. A small percentage of patients with Turner's syndrome have a complex mosaic karyotype with atypical clinical features and mental retardation.Methods/Patient: We report the first case of a child with a complex mosaic Turner genotype and hyperinsulinaemic hypoglycaemia responsive to diazoxide therapy.Results: Cytogenetic analysis showed four cell lines: one with 45,X; the others with an additional small ring chromosome, a small marker chromosome, and both the ring and marker chromosomes, respectively. FISH studies showed the abnormal chromosomes to originate from an X. The X inactivation locus (XIST) was present in the ring, but not in the marker chromosome.Conclusions: The recognition of hypoglycaemia in children with atypical Turner's syndrome is important as persistent hypoglycaemia may lead to brain damage in addition to the risk of mental retardation. Further studies are required to understand whether the mosaic over- or under-expression of unidentified X chromosome gene(s) in the pancreatic beta-cells leads to hyperinsulinaemic hypoglycaemia.