Novel compound heterozygous mutation in STAMBP causes a neurodevelopmental disorder by disrupting cortical proliferation

AAV-mediated Stambp gene replacement therapy rescues neurological defects in a mouse model of microcephaly-capillary malformation syndrome

The microcephaly-capillary malformation (MIC-CAP) syndrome is a life-threatening disease caused by biallelic mutations of the STAMBP gene, which encodes an endosomal deubiquitinating enzyme. To establish a suitable preclinical animal model for clinical therapeutic practice, we generated a central nervous system (CNS)-specific Stambp knockout mouse model (Stambp Sox1-cKO) that phenocopies Stambp null mice including progressive microcephaly, postnatal growth retardation and complete penetrance of preweaning death. In this MIC-CAP syndrome mouse model, early-onset neuronal death occurs specifically in the hippocampus and cortex, accompanied by aggregation of ubiquitinated proteins, and massive neuroinflammation. Importantly, neonatal AAV9-mediated gene supplementation of Stambp in the brain could significantly improve neurological defects, sustain growth, and prolong the lifespan of StambpSox1-cKO mice. Together, our findings reveal a central role of brain defects in the pathogenesis of STAMBP deficiency and provide preclinical evidence that postnatal gene replacement is an effective approach to cure the disease.

STAMBP is Required for Long-Term Maintenance of Neural Progenitor Cells Derived from hESCs

Mutations in STAMBP have been well-established to cause congenital human microcephaly-capillary malformation (MIC-CAP) syndrome, a rare genetic disorder characterized by global developmental delay, severe microcephaly, capillary malformations, etc. Previous biochemical investigations and loss-of-function studies in mice have provided insights into the mechanism of STAMBP, however, it remains controversial how STAMBP deficiency leads to malformation of those affected tissues in patients. In this study, we investigated the function and underlying mechanism of STAMBP during neural differentiation of human embryonic stem cells (hESCs). We found that STAMBP is dispensable for the pluripotency maintenance or neural differentiation of hESCs. However, neural progenitor cells (NPCs) derived from STAMBP-deficient hESCs fail to be long-term maintained/expanded in vitro. We identified the anti-apoptotic protein CFLAR is down-regulated in those affected NPCs and ectopic expression of CFLAR rescues NPC defects induced by STAMBP-deficiency. Our study not only provides novel insight into the mechanism of neural defects in STAMBP mutant patients, it also indicates that the death receptor mediated apoptosis is an obstacle for long-term maintenance/expansion of NPCs in vitro thus counteracting this cell death pathway could be beneficial to the generation of NPCs in vitro.

Novel STAMBP mutations in a Chinese girl with rare symptoms of microcephaly-capillary malformation syndrome and Mowat-Wilson syndrome

Microcephaly-capillary malformation syndrome (MIC-CAP) and Mowat-Wilson syndrome (MWS) are both rare hereditary diseases with several overlapping symptoms. We here report a Chinese patient simultaneously affected by MIC-CAP and MWS, presenting with moderate anaemia because of repeated, unilateral refractory epistaxis. The girl was initially diagnosed with MWS after discovery of a pathogenic nonsense mutation in ZEB2. Starting from the age of 3 years old, the child experienced repeated epistaxis on the right side without obvious incentive or trauma. The bleeding was quite difficult to stop and her hemoglobin dropped from 124 g/L to 64 g/L in three months. Both coagulation disorders and allergic rhinitis were excluded by extensive workup and experimental therapeutics. Retrospective genetic analysis revealed that she carried two novel compound heterozygous mutations in STAMBP (c.610T > C: p.Ser204Pro and c.945C > G: p.Asn315Lys). This case report demonstrates a rare presentation of MIC-CAP in the pediatric population and enriches the variant spectrum of STAMBP.