L-Serine is a proteinogenic amino acid synthesized in the body from other metabolites, such as glycine. Functionally, L-serine (or serine) plays a role in the biosynthesis of purines and pyrimidines and is an important component of metabolism. L-serine is also a precursor to a number of amino acids and metabolites, helps catalyze enzymes, and activates NMDA receptors in the brain. 

According to a study conducted at Harvard Medical School, supplementation of the amino acid L-serine may also be a beneficial treatment for a disorder called hereditary sensory and autonomic neuropathy type 1 (HSAN1). HSAN1 is characterized by hyperpathia (where nociceptive stimuli evoke exaggerated levels of pain) and spontaneous shooting pains, followed by sensory loss that usually affects the lower limbs.

Due to the drastic sensory impairment, individuals with HSAN1 may develop neuropathic ulcers and degeneration of joints, which may ultimately lead to amputation of the affected limbs.

Because HSAN1 is caused by mutations in the genes of the enzyme serine palmitoyltransferase (SPT), researchers Kevin Garofalo et al. hypothesize that administration of oral L-serine supplements would decrease the severity of HSAN1 symptoms. They believe that L-serine would decrease the levels of the neurotoxic deoxysphingolipids (dSLs) presented in HSAN1 patients.

The researchers first tested L-serine and L-alanine supplements in mice with a mutation that closely mimics the HSAN1 disorder in humans. They found that in varying mutations of mice, L-serine supplements inhibited dSL production and the mice demonstrated better neurological performance and increased male fertility.

Meanwhile, L-alanine supplements increased dSL levels and worsened symptoms of the disease in mice, some of them developing skin ulcers and showing extreme sensation loss.

The effect of L-serine supplements on HSAN1 symptoms

In the human trial, the researchers recruited HSAN1 patients and supplemented their diets with L-serine. They found that treatment resulted in a significant, albeit slower, reduction of plasma dSL levels than found in the mice.

After six weeks of L-serine supplementation, the researchers said that all but one patient had dSL levels very close to that of the control group. Treated patients also reported more feeling in sensations such as menstrual cramps and tingling hands.

Based on these results, the researchers believe that L-serine supplementation is of great value in helping treat HSAN1 neuropathy disorder but more studies will be necessary to examine the long-term effects.