Type of disease: Rare conditions
Hereditary hyperekplexia is an inherited condition that is usually evident in infants. Symptoms include increased muscle tone (hypertonia) and an exaggerated startle reaction to unexpected stimuli, especially loud noises. Following the startle reaction, infants experience a brief period in which they are very rigid and unable to move. During these rigid periods, some infants stop breathing, which can be fatal. This may explain some cases of sudden infant death syndrome (SIDS). Symptoms typically fade by age 1. However, older individuals with this condition may still startle easily and have periods of rigidity. Others may have a low tolerance for crowded places and loud noises. This condition has different inheritance patterns and is associated with mutations in at least five genes. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.