Olfaction and substantia nigra echogenicity in young individuals with 22q11.2 deletion syndrome, a population at high risk for dopaminergic neuropsychiatric disease

Purpose Individuals with 22q11.2 deletion syndrome (22q11.2DS) show a wide range of somatic features. The syndrome also leads to increased prevalence of neuropsychiatric disorders including schizophrenia, attention deficit hyperactivity disorder and early-onset Parkinson’s disease, presumably mediated by alterations in dopaminergic neurotransmission. Diagnostic biomarkers already in clinical use for Parkinson’s disease are increased size of the echogenic area of the substantia nigra (SN) and reduced olfactory function. The aim of the study was to investigate these two characteristics in patients with 22q11.2DS but without Parkinson’s disease. Methods Olfactory function (sensitivity and discrimination) was assessed with the Sniffin’ Sticks test. The maximal size of the echogenic area of the substantia nigra (SNmax in mm 2 ) in transcranial sonography was evaluated by two raters blinded to subjects’ clinical status. Findings of patients with 22q11.2DS and controls were compared in analyses of covariance. Results The sample for assessment of olfactory function comprised N = 60 patients ( N = 37 males, m = 17.3 ± 8.8 years) and N = 60 controls. The sample for assessment of SN echogenicity comprised N = 50 patients ( N = 30 males, m = 16.02 ± 7.8 years) and N = 50 controls. The group with 22q11.2DS showed impaired olfactory sensitivity (F 1,105 = 36.109, p < .001, partial eta 2 = .256) and discrimination (F 1,109 = 51.248, p < .001, partial eta 2 = .320) compared to controls. No significant group differences could be observed with regard to the SNmax ( p = 0.167). Conclusions In this young sample previous findings demonstrating reduced olfactory function in 22q11.2DS were replicated, whereas no significant changes in echogenicity of SN were detected.