Introduction: The pontocerebellar hypoplasia type 1 is characterized by cerebellar and brainstem malformation, associated to spinal cord anterior horn degeneration. It is a rare cause of severe global hypotonia of genetic etiology and with poor prognosis.

Case description: M.A.O., female, admitted at 43 days of life for investigation of global hypotonia and facial assimetry. Born at term, appropriate for gestational age, pregnancy and delivery occurred uneventfully, no family history of consanguinity. At examination showed facial dismorphies, hypoactivity and hyporeactivity, severe global hypotonia with diffuse muscular hypotrophy and hyporeflexia, reduced force in all limbs, but no fasciculation.

At follow up presented important psychomotor development delay without seizures. Diagnostic investigation showed MRI (at 3 months) with important reduction of volume in pons, vermis and cerebellar hemispheres and electromyography (at 5 months) compatible with axonopathy in spinal anterior horn at cervical and lumbosacral segments. Other exams like echocardiogram, abdominal USG, muscle enzimes, tandem mass spectrometry, test for pompe disease, karyotype, transferrin isofocusing, lactate, blood gases and EEG all came out normal. It was proposed the diagnosis of pontocerebellar hypoplasia type 1, still waiting genetic confirmation. Recurrent respiratory infections leaded to death at 16 months of age.

Conclusion: The investigation of floppy infant syndrome begins with semiological and topographic differentiation between central and peripheral alterations. Pontocerebellar hypoplasia type 1 affects both central and peripheral levels and should be considered in this diferencial diagnosis, despite of its rarity.