Intractable Epileptic Spasms in a Patient with Pontocerebellar Hypoplasia: Severe Phenotype of Type 2 or Another Subtype?

INTRODUCTION:Pontocerebellar hypoplasia (PCH) involves a diverse range of etiologies including a group of single gene disorders. Mutations in the tRNA splicing endonuclease complex (TSEN) 54 gene can be responsible for PCH type 2, 4 and 5. The more common and less severe PCH 2 phenotype is caused by homozygosity for the common missense mutation A307S, while the severe phenotype seen in type 4 and 5 is caused by compound heterozygosity of the A307S mutation along with a nonsense or splice site mutation.REPORT:We report a 4- month-old girl who presented with epileptic spasms that remained intractable to several antiepileptic medications. Magnetic Resonance Imaging (MRI) brain showed fairly severe hypoplasia with superimposed atrophy of the cerebellum and brainstem with prominent extra-axial fluid spaces. Extensive metabolic testing was negative. Commercial testing for PCH via TSEN54 gene revealed missense mutation of Ala307Ser. A novel sequence variant, designated c.17_40 del, was also found and was predictive of an in-frame deletion of eight amino acids. Follow-up over 2 years revealed intractable epileptic spasms, progressive microcephaly and development of prominent choreoathetosis.CONCLUSION:This case report describes a rare case of PCH with overlapping features of the less severe PCH2 and the more severe PCH4/5 phenotype. It also adds another new entity in the list of genetic conditions where West syndrome and pontocerebellar hypoplasia can be seen together, emphasizing the need for further investigations of the genotype-phenotype correlation of mutations in order to advance our understanding of the pathophysiologic mechanism in these rare conditions.