Kosaki overgrowth syndrome (KOGS) and Penttinen syndrome (PS) are extremely rare multisystem disorders caused by heterozygous activating variants of the PDGFRB gene. KOGS results in characteristic craniofacial, orthopedic, skin and neurological disorders. PS is a progeroid disease responsible for a prematurely aged appearance. Patients suffer significant morbidity and mortality due to various complications. Tyrosine Kinase Inhibitors (TKIs) targeting PGDFRB appear to be a potential treatment option, as evidenced by a few case reports showing clinical improvement in some patients, with modest and self-resolving side effects. The natural history of these two syndromes remains poorly understood as only case-reports have been published.

Therefore, an international consortium was created in December 2019 by Pr FAIVRE (CHU Dijon Bourgogne & ERN ITHACA) to follow treated and untreated patients in a real-life, multicentre, observational study, in order to expand our knowledge of these ultra-rare diseases. In the longer term, we believe that TKIs could bring clinical benefit to KOGS/PS patients.

Inclusion Criteria:

• Clinical diagnosis of Kosaki or Penttinen syndrome
• Molecular diagnosis of an activating variant in PDGFRB gene
• Patient who has been informed and provide a written informed consent

Exclusion Criteria:

• Absence of clinical diagnosis of Kosaki or Penttinen syndrome
• Absence of molecular diagnosis of an activating variant in the PDGFRB gene.
• Patient who has not been informed and/or did not provide a written informed consent.

All patients with KOGS or PS due to PDGFRB activating variants