Background Alkaptonuria (AKU) is a serious genetic disease characterised by premature spondyloarthropathy. Homogentisate-lowering therapy is being investigated for AKU. Nitisinone decreases homogentisic acid (HGA) in AKU but the dose-response relationship has not been previously studied. Methods Suitability Of Nitisinone In Alkaptonuria 1 (SONIA 1) was an international, multicentre, randomised, open-label, no-treatment controlled, parallel-group, dose-response study. The primary objective was to investigate the effect of different doses of nitisinone once daily on 24-h urinary HGA excretion (u-HGA₂₄) in patients with AKU after 4 weeks of treatment. Forty patients were randomised into five groups of eight patients each, with groups receiving no treatment or 1 mg, 2 mg, 4 mg and 8 mg of nitisinone. Findings A clear dose-response relationship was observed between nitisinone and the urinary excretion of HGA. At 4 weeks, the adjusted geometric mean u-HGA₂₄ was 31.53 mmol, 3.26 mmol, 1.44 mmol, 0.57 mmol and 0.15 mmol for the no treatment or 1 mg, 2 mg, 4 mg and 8 mg doses, respectively. For the most efficacious dose, 8 mg daily, this corresponds to a mean reduction of u-HGA₂₄ of 98.8% compared with baseline. An increase in tyrosine levels was seen at all doses but the dose-response relationship was less clear than the effect on HGA. Despite tyrosinaemia, there were no safety concerns and no serious adverse events were reported over the 4 weeks of nitisinone therapy. Conclusions In this study in patients with AKU, nitisinone therapy decreased urinary HGA excretion to low levels in a dose-dependent manner and was well tolerated within the studied dose range. Trial registration number EudraCT number: 2012-005340-24. Registered at ClinicalTrials.gov: NCTO1828463.

Nonsense, missense, and even silent mutation‐associated exon skipping is recognized in an increasing number of genes as a novel form of splicing mutation. The analysis of individual mutations of this kind can shed light on basic pre‐mRNA splicing mechanisms. Using cDNA‐based mutation detection analysis, we have identified one missense and six nonsense mutations that lead to different extents of exon‐lacking transcripts in neurofibromatosis type 1 (NF1) patients. We confirmed mutation‐associated exon skipping in a heterologous hybrid minigene context. There is evidence that the disruption of functional exonic splicing enhancer (ESE) sequences is frequently the mechanism underlying mutation‐associated exon skipping. Therefore, we examined the wild‐type and mutant NF1 sequences with two available ESE‐prediction programs. Either or both programs predicted the disruption of ESE motifs in six out of the seven analyzed mutations. To ascertain the function of the predicted ESEs, we quantitatively measured their ability to rescue splicing of an enhancer‐dependent exon, and found that all seven mutant ESEs had reduced splicing enhancement activity compared to the wild‐type sequences. Our results suggest that the wild‐type sequences function as ESE elements, whose disruption is responsible for the mutation‐associated exon skipping observed in the NF1 patients. Further, this study illustrates the utility of ESE‐prediction programs for delineating candidate sequences that may serve as ESE elements. However, until more refined prediction algorithms have been developed, experimental data, preferably from patient tissues, remain indispensable to assess the clinical significance, particularly of missense and silent mutations, and to understand the structure–function relationship in the corresponding protein. Hum Mutat 24:491–501, 2004.