Sotos syndrome is a rare genetic disorder characterized by overgrowth associated 
with macrocephaly and delayed psychomotor development. Patients with Sotos 
syndrome show 5q35 deletions involving NSD1 or its point mutations. We 
identified the common 5q35 deletion in a patient with atypical Sotos syndrome 
manifesting extremely severe developmental delay, joint hypermobility, and skin 
hyperextensibility, which are recognized as Marfanoid hypermobility syndrome. 
Further analyses were performed to identify the genetic cause of these 
additional findings. aCGH analysis revealed an additional 862 kb deletion of 
Xq22.3 in this patient, which was inherited from his healthy mother. The deleted 
region included five genes, including the nik-related kinase gene (NRK), which 
would be a candidate gene for the patient's Marfanoid hypermobility, because it 
is a member of the glucokinase subfamily that are involved in activating the JNK 
pathway, and is expressed in developing skeletal musculature. Severe 
developmental delay seen in the patient may be derived from position effect of 
the deletion for neighboring interleukin 1 receptor accessory protein-like 2 
gene (IL1RAPL2), which is a candidate gene for X-linked mental retardation.