Genetic mutation in pontocerebellar hypoplasia

Pontocerebellar hypoplasia in association with de novo 19p13.11p13.12 microdeletion

The pontocerebellar hypoplasias (PCHs) are a group of clinically variable disorders characterized by abnormally small cerebellum and brainstem, generally inherited in an autosomal recessive pattern. While PCHs have been grouped into six subtypes, clinical diagnosis is equivocal until a genetic diagnosis is established. We report a patient with PCH, intrauterine growth restriction, ventricular septal defect, rib anomalies, midgut malrotation, and facial dysmorphic features. Using SNP analysis, we identified three de novo deletions of: 1.055 Mb at 6q24.3q25.1 (148174730-149229583); 169 kb at 16p13.2 (6565411-6733934); and 2.530 Mb at 19p13.11p13.12 (13857587-16387798), which were confirmed by FISH. 19p13 deletions are rare aberrations. Of patients previously described with overlapping 19p13.12 deletions and multiple anomalies, only one presented with PCH. Deleted in both that patient and the patient reported here, is DDX39, a DEAD-box RNA helicase. DDX39 is part of the homeostatic machinery that regulates the switch of cellular proliferation and differentiation. It is highly expressed in the developing central nervous system and optic cup of Xenopus laevis. The brain abnormalities in the patient reported here were more severe than the previously reported patient, which may be due to additional deletions or undetected point mutations in the nondeleted allele. Notably, the patient reported here also has a partial deletion of RBFOX1 (A2BP1), which lies within the autism susceptibility locus on 16p13.2. Our findings suggest chromosomal microarray analysis may be useful in determining etiology of syndromic PCH.

Pontocerebellar hypoplasia: review of classification and genetics, and exclusion of several genes known to be important for cerebellar development

The pontocerebellar hypoplasias are a heterogeneous group of rare and devastating conditions characterized by multiple structural abnormalities of the ventral pons, inferior olive, and cerebellum. Here, we briefly review these conditions and discuss genes recently discovered to be involved in pontocerebellar hypoplasia pathogenesis. We then present data that exclude several genes important for cerebellar development as causes of pontocerebellar hypoplasia-4 and pontocerebellar hypoplasia-5, and we demonstrate that not all cases of clinically defined pontocerebellar hypoplasia-4 result from mutations in TSEN54. We conclude that classification based on clinical, imaging, and neuropathological findings does not differentiate between pontocerebellar hypoplasia subtypes with different genetic causes.