Exostoses, enchondromatosis and metachondromatosis; diagnosis and management.

We describe a 5 years old girl who presented to the multidisciplinary skeletal dysplasia clinic following excision of two bony lumps from her fingers. Based on clinical examination, radiolographs and histological results an initial diagnosis of hereditary multiple exostosis (HME) was made. Four years later she developed further lumps which had the radiological appearance of enchondromas. The appearance of both exostoses and enchondromas suggested a possible diagnosis of metachondromatosis. Genetic testing revealed a splice site mutation at the end of exon 11 on the PTPN11 gene, confirming the diagnosis of metachondromatosis. While both single or multiple exostoses and enchondromas occur relatively commonly on their own, the appearance of multiple exostoses and enchondromas together is rare and should raise the differential diagnosis of metachondromatosis. Making this diagnosis is important as the lesions in metachondromatosis may spontaneously resolve and therefore surgical intervention is often unnecessary. We discuss the diagnostic findings, genetic causes, treatment and prognosis of this rare condition of which less than thirty cases have previously been reported.

De novo heterozygous mutations in SMC3 cause a range of Cornelia de Lange syndrome-overlapping phenotypes.

Cornelia de Lange syndrome (CdLS) is characterized by facial dysmorphism, growth failure, intellectual disability, limb malformations, and multiple organ involvement. Mutations in five genes, encoding subunits of the cohesin complex (SMC1A, SMC3, RAD21) and its regulators (NIPBL, HDAC8), account for at least 70% of patients with CdLS or CdLS-like phenotypes. To date, only the clinical features from a single CdLS patient with SMC3 mutation has been published. Here, we report the efforts of an international research and clinical collaboration to provide clinical comparison of 16 patients with CdLS-like features caused by mutations in SMC3. Modeling of the mutation effects on protein structure suggests a dominant-negative effect on the multimeric cohesin complex. When compared with typical CdLS, many SMC3-associated phenotypes are also characterized by postnatal microcephaly but with a less distinctive craniofacial appearance, a milder prenatal growth retardation that worsens in childhood, few congenital heart defects, and an absence of limb deficiencies. While most mutations are unique, two unrelated affected individuals shared the same mutation but presented with different phenotypes. This work confirms that de novo SMC3 mutations account for ∼ 1%-2% of CdLS-like phenotypes.