The neurometabolic disorder glutaric aciduria type 1 (GA1) is caused by mutations in the GCDH gene encoding the mitochondrial matrix protein glutaryl-CoA dehydrogenase (GCDH), which forms homo- and heteromeric complexes. Twenty percent of all pathogenic mutations affect single amino acid residues on the surface of GCDH resulting in a severe clinical phenotype. We report here on heterologous expression studies of 18 missense mutations identified in GA1 patients affecting surface amino acids. Western blot and pulse chase experiments revealed that the stability of half of the GCDH mutants was significantly reduced. In silico analyses showed that none of the mutations impaired the 3D structure of GCDH. Immunofluorescence co-localisation studies in HeLa cells demonstrated that all GCDH mutants were correctly translocated into mitochondria. Surprisingly, the expression of p.Arg88Cys GCDH as well as further substitutions by alanine, lysine, or methionine but not histidine or leucine resulted in the disruption of mitochondrial architecture forming longitudinal structures composed of stacks of cristae and partial loss of the outer mitochondrial membrane. The expression of mitochondrial fusion or fission proteins was not affected in these cells. Bioluminescence resonance energy transfer analyses revealed that all GCDH mutants exhibit an increased binding affinity to electron transfer flavoprotein beta, whereas only p.Tyr155His GCDH showed a reduced interaction with dihydrolipoamide succinyl transferase. Our data underscore the impact of GCDH protein interactions mediated by amino acid residues on the surface of GCDH required for proper enzymatic activity.

Gaucher Disease (GD) 2 is a rare inherited lysosomal disorder. Early-onset and rapid progression of neurovisceral symptoms lead to fatal outcome in early childhood. Treatment is symptomatic, a curative therapy is currently not available. This prospective study describes the clinical and biochemical outcome of a GD 2 patient treated with high dose ambroxol from the age of 4 months. Due to progressive hepatosplenomegaly additional enzyme replacement therapy was required 1 year after ambroxol monotherapy was initiated. Detailed clinical follow-up data demonstrated an age-appropriate neurocognitive and motor development but no clear benefit on peripheral organs. Glucosylsphingosine (Lyso-GL1) in cerebrospinal fluid decreased remarkably compared to pre-treatment, whereas Lyso-GL1 and chitotriosidase in blood increased. Ambroxol treatment of patient fibroblasts revealed a significant increase in β-glucocerebrosidase activity in vitro. To our knowledge, this is the first report of a GD 2 patient with age-appropriate cognitive and motor development at 3 years of age. Combination of high dose ambroxol with ERT proved to be a successful approach to manage both visceral and neurological manifestations.

Introduction The pathophysiological significance of the Fabry‐related, non‐classical variant p.D313Y still remains to be solved. This study assesses the involvement of the peripheral nervous system with respect to small fiber neuropathy and neuropathic pain in female patients carrying p.D313Y. Methods This study examined nine females carrying the Fabry‐related p.D313Y variant by obtaining skin punch biopsies above the right lateral malleolus. Intraepidermal nerve fiber density was determined for each patient and compared to reference values matched for the patientʼs decade of life and sex. Moreover, each patient was characterized by a detailed neurological examination and by pain assessment via questionnaire. Results Compared to sex‐matched lower fifth percentile reference values per decade, intraepidermal nerve fiber density was decreased in seven out of nine patients. Four patients reported acral paresthesias and neuropathic pain with an average visual analogue scale score of 7 out of 10 points. Two patients experienced acute pain crises. Six out of seven patients diagnosed with small fiber neuropathy had a their medical history of hypo‐ and/or hyperhidrosis. Discussion The diagnosis of small fiber neuropathy was made in seven out of nine females carrying the non‐classical variant p.D313Y. Moreover, neuropathic pain and symptoms indicative of autonomic nervous system dysfunction seem to be common findings that may be of clinical significance and may warrant therapeutic intervention.