SNP Shot: Genomic Insights

Hereditary sensory and autonomic neuropathy type II (HSAN2) is a disorder that primarily affects sensory nerve cells (sensory neurons). These neurons are responsible for transmitting information about sensations like pain, temperature, and touch to the brain. Individuals with HSAN2 experience impaired sensation. Some may also have mild problems with autonomic neurons, which control involuntary body functions such as heart rate, digestion, and breathing. Both sensory and autonomic neurons are part of the peripheral nervous system, the network of nerves located outside the brain and spinal cord. Therefore, HSAN2 is categorized as a type of peripheral neuropathy.

The signs and symptoms of HSAN2 usually appear in infancy or early childhood. Typically, the first sign is numbness in the hands and feet. Soon after, individuals lose the ability to feel pain or distinguish between hot and cold. This lack of sensation often leads to unnoticed injuries that develop into open sores (ulcers) on the hands and feet. Because they cannot feel the pain, affected individuals may delay seeking treatment. If left untreated, these ulcers can become infected and potentially require amputation. People with HSAN2 commonly injure themselves unintentionally, for example, by biting their tongue, lips, or fingers. These injuries can result in the loss of tissue, such as the tip of the tongue. Due to their inability to feel pain, affected individuals often have untreated injuries and fractures in their hands, feet, limbs, and joints. Repeated injury can lead to Charcot joints, a condition where the bones and surrounding tissue of joints are damaged.

The impact of HSAN2 on the autonomic nervous system varies. Some infants with HSAN2 experience digestive issues like gastroesophageal reflux (the backflow of stomach acids into the esophagus) or have slow eye-blink or gag reflexes. Affected individuals might also have weak deep-tendon reflexes, such as the knee-jerk reflex tested by a doctor.

Some individuals with HSAN2 lose lingual fungiform papillae, a type of taste bud on the tip of the tongue, resulting in a reduced sense of taste.

Inheritance:

HSAN2 is inherited in an autosomal recessive manner. This means that an individual must inherit two copies of the mutated gene (one from each parent) to develop the condition. The parents, who each carry only one copy of the mutated gene, typically do not exhibit any signs or symptoms of HSAN2.