Carbidopa for the Treatment of Nausea and Vomiting in Familial Dysautonomia

Patients with familial dysautonomia (FD), also called Riley Day syndrome or hereditary sensory and autonomic neuropathy type III, suffer recurrent attacks of uncontrollable nausea and vomiting that can last several hours or days and are severely disabling. Hypertension, tachycardia and skin blotching frequently accompany these attacks. Our long-term objective is to develop an effective treatment for nausea and vomiting in patients with FD. In preliminary studies we found that plasma levels of dopamine were very high during attacks. Stimulation of dopamine receptors in the chemoreceptor trigger zone in the brainstem is a well-known cause of nausea and vomiting. The investigators postulate that acute increases in circulating dopamine levels are the cause of paroxysmal nausea and vomiting in FD. Dopamine is synthesized by decarboxylation of the aminoacid L-dihydroxyphenylserine (L-DOPA) by the enzyme aromatic L-aminoacid decarboxylase, also known as DOPA decarboxylase. Patients with Parkinson's disease suffer nausea and vomiting when they receive treatment with L-DOPA. However, when L-DOPA is administered together with carbidopa, a reversible competitive inhibitor of DOPA decarboxylase that does not cross the blood brain barrier, nausea and vomiting are prevented. The investigators hypothesize that by blocking the conversion of DOPA to dopamine and thus preventing its increase in plasma, treatment with carbidopa will decrease nausea and vomiting in patients with FD. Although carbidopa has been used for many years in patients with Parkinson's disease, it has never been used in patients with FD. The first specific aim of this proposal is to assess the safety and tolerability of carbidopa in patients with FD. The second specific aim of this proposal is to determine whether blocking the peripheral synthesis of dopamine with carbidopa will improve recurrent nausea in patients with FD.