Stiff baby syndrome, scientifically referred to as hyperexplexia, is a genetic condition characterized by an intensified startle reflex in infants. This disorder was first identified in 1962 by Drs. Kok and Bruyn. It presents at birth with symptoms that include body stiffness, an exaggerated startle response, pronounced brain-stem reflexes, particularly the head-retraction reflex, and occasionally other symptoms. The hypertonia, or stiffness, is noticeable in the limbs, tends to disappear during sleep, and gradually decreases during the first year of life. In some instances, the startle reflex is accompanied by sudden, intense stiffness, causing individuals to fall abruptly. The disorder has appeared in 29 males and females across six generations, suggesting it is an autosomal (non-sex-linked) genetic condition.Since its discovery, additional families have been diagnosed with this condition. Other associated symptoms include a tendency towards umbilical and other hernias, likely due to increased abdominal pressure, and hip dislocation. The heightened startle reflex persists throughout a person’s life, triggered by light touches to the nose, loud noises such as clapping, or sudden movements such as jolting a chair. The gene linked to this disorder is located on chromosome 5, specifically in the 5q33.2-q33.3 bands, and involves a mutation in the gene for the alpha-1 subunit of the receptor.Treatment typically involves medication, with clonazepam (KLONOPIN) being effective in managing neurological symptoms. In some cases, phenobarbital, diazepam (VALIUM), and valproic acid (DEPAKENE) are also beneficial. Hyperexplexia is alternatively known as Kok disease, startle disease, exaggerated startle reflex, or hyperekplexia.
