Monoamine oxidase A (MAO A) is a key enzyme for serotonin metabolism. Knockout MAO A in mice results in elevated serotonin, altered serum autoantibodies, and autistic-like behavior. There is a subset of patients with autism spectrum disorder (ASD) who exhibit hyperserotonemia. The link between the MAO A, hyperserotonemia, immunity, and ASD is still unknown. To address this question, we harness the high-density human proteome microarray to profile the serum autoantibodies in ASD patients with or without MAO A deficiency. We recruited 25 subjects, including 20 ASD patients, from National Yang Ming Chiao Tung University Hospital and determined their plasma serotonin levels, screened for MAO A gene mutations and identified one patient with a C374 G mutation, which abolished MAO A activity and showed the highest serotonin level (hsASD; 518.42 ng/ml) and severe ASD symptoms. In another family with twin brothers, one was diagnosed with mild ASD and exhibited an increased serotonin level (isASD; 31.48 ng/ml), while the other twin was a healthy control. These three subjects were used for serum autoantibody profiling using high-density human proteome microarrays. Comparing serum antibodies from hsASD with healthy control, we identified 354 up-regulated and 398 down-regulated autoantibodies in hsASD. By comparing isASD with healthy controls, we reported 235 up-regulated and 279 down-regulated autoantibodies in isASD. Interestingly, the up-regulated autoantibodies for hsASD were enriched in the brain region and exhibited distinct features from that of isASD. This study indicates that MAO A deficiency and serotonin levels significantly impact the immunological changes in ASD patients, which may shed some light on pathological mechanisms and provide potential biomarkers for translational research in ASD.

Inherited disorders of neurotransmitter metabolism are a group of rare diseases, which are caused by impaired synthesis, transport, or degradation of neurotransmitters or cofactors and result in various degrees of delayed or impaired psychomotor development. To assess the effect of neurotransmitter deficiencies on intelligence, quality of life, and behavior, the data of 148 patients in the registry of the International Working Group on Neurotransmitter Related Disorders (iNTD) was evaluated using results from standardized age-adjusted tests and questionnaires. Patients with a primary disorder of monoamine metabolism had lower IQ scores (mean IQ 58, range 40-100) within the range of cognitive impairment (<70) compared to patients with a BH4 deficiency (mean IQ 84, range 40-129). Short attention span and distractibility were most frequently mentioned by parents, while patients reported most frequently anxiety and distractibility when asked for behavioral traits. In individuals with succinic semialdehyde dehydrogenase deficiency, self-stimulatory behaviors were commonly reported by parents, whereas in patients with dopamine transporter deficiency, DNAJC12 deficiency, and monoamine oxidase A deficiency, self-injurious or mutilating behaviors have commonly been observed. Phobic fears were increased in patients with 6-pyruvoyltetrahydropterin synthase deficiency, while individuals with sepiapterin reductase deficiency frequently experienced communication and sleep difficulties. Patients with BH4 deficiencies achieved significantly higher quality of life as compared to other groups. This analysis of the iNTD registry data highlights: (a) difference in IQ and subdomains of quality of life between BH4 deficiencies and primary neurotransmitter-related disorders and (b) previously underreported behavioral traits.

Inherited monoamine neurotransmitter disorders (iMNDs) are rare disorders with clinical manifestations ranging from mild infantile hypotonia, movement disorders to early infantile severe encephalopathy. Neuroimaging has been reported as non-specific. We systematically analyzed brain MRIs in order to characterize and better understand neuroimaging changes and to re-evaluate the diagnostic role of brain MRI in iMNDs. 81 MRIs of 70 patients (0.1-52.9 years, 39 patients with tetrahydrobiopterin deficiencies, 31 with primary disorders of monoamine metabolism) were retrospectively analyzed and clinical records reviewed. 33/70 patients had MRI changes, most commonly atrophy (n = 24). Eight patients, six with dihydropteridine reductase deficiency (DHPR), had a common pattern of bilateral parieto-occipital and to a lesser extent frontal and/or cerebellar changes in arterial watershed zones. Two patients imaged after acute severe encephalopathy had signs of profound hypoxic-ischemic injury and a combination of deep gray matter and watershed injury (aromatic l-amino acid decarboxylase (AADCD), tyrosine hydroxylase deficiency (THD)). Four patients had myelination delay (AADCD; THD); two had changes characteristic of post-infantile onset neuronal disease (AADCD, monoamine oxidase A deficiency), and nine T2-hyperintensity of central tegmental tracts. iMNDs are associated with MRI patterns consistent with chronic effects of a neuronal disorder and signs of repetitive injury to cerebral and cerebellar watershed areas, in particular in DHPRD. These will be helpful in the (neuroradiological) differential diagnosis of children with unknown disorders and monitoring of iMNDs. We hypothesize that deficiency of catecholamines and/or tetrahydrobiopterin increase the incidence of and the CNS susceptibility to vascular dysfunction.