Child Neurology: Arthrogryposis and Antenatal-Onset Hyperkinetic Movements in a Newborn

The evolving field of fetal neurology can offer insights into early nervous system development through antenatal dynamic ultrasonography and maternal perception of movements. The spectrum of abnormal fetal movements ranges from fetal akinesia, often associated with arthrogryposis multiplex congenita (AMC), to increased repetitive movements, typically indicating fetal seizures. Nonepileptic hyperkinetic movement disorders of the fetus are rarely documented. Here, we report a female infant who had clonus-like movements in utero and postnatally. Antenatal ultrasonography revealed polyhydramnios, fetal growth restriction, and repetitive clonus-like movements (∼5 Hz), which the mother perceived as frequently "shaking" her. The infant required resuscitation and intubation at delivery. AMC, ectrodactyly, cataract, axial hypotonia, and absent primitive reflexes were noted, along with persistent high-frequency, low-amplitude clonus-like movements without accompanying ictal epileptic activity on the EEG. Laboratory findings included markedly elevated serum creatine kinase levels attributed to sustained contractions, severe neutropenia, and 3-methylglutaconic aciduria. Despite supportive care, she died of respiratory failure on day 15. Whole-exome sequencing established the diagnosis as caseinolytic peptidase B deficiency, an autosomal recessive primary mitochondrial disorder caused by pathogenic variants in the nuclear-encoded CLPB gene. This is a unique case of AMC, paradoxically occurring with hyperkinesia rather than with global hypokinesia, but the hyperkinetic movement repertoire is limited and restrictive. This case underlines the diagnostic value of integrating antenatal history and imaging with detailed postnatal phenotyping by a multidisciplinary team in neurometabolic disorders.