Clinical: Almost all patients have some degree of mental retardation and facial dysmorphism (round face, deep-set eyes, thin upper lip). Behavioural problems are common. Brachymetaphalangism is reported in ~50% of cases overall, but is typically not evident below the age of 2 years. There is striking phenotypic variability, and the size and extent of the deleted region cannot be used as accurate predictors of prognosis. Some patients have additional problems eg. congenital heart disease and seizures.

Size of deletion: Variable. No common breakpoints indicating that 2q37 rearrangement is unlikely to be mediated by non-homologous recombination and low-copy repeats (Aldred). The minimum deleted region in pateints with characteristic facial dysmorphism and Albright hereditary osteodystrophy (AHO)-like brachymetaphalangism has been narrowed to ~3Mb. In Aldred's series of 20 patients, no clear relationship was found between clinical features and the size or position of the monosomic region.

Origin of deletion: Almost all are terminal deletion. There is a high frequency of de novo deletions, but familial cases are observed. Equal proportions of maternally and paternally derived rearrangements were seen in Aldred's series.

Expert adviser: Dr Richard Trembath, Professor of Medical Genetics, Guy's Hospital, London, UK and Dr Micheala Aldred, Senior Lecturer in Medical Molecular Genetics, University of Leicester, UK

Links to support groups:

www.rarechromo.org

Links to further information:

www.ncbi.nlm.nih.gov

www.orpha.net