BackgroundActivating mutations in the GLUD1 gene (which encodes for the intra-mitochondrial enzyme glutamate dehydrogenase, GDH) cause the hyperinsulinism–hyperammonaemia (HI/HA) syndrome. Patients present with HA and leucine-sensitive hypoglycaemia. GDH is regulated by another intra-mitochondrial enzyme sirtuin 4 (SIRT4). Sirt4 knockout mice demonstrate activation of GDH with increased amino acid-stimulated insulin secretion.ObjectivesTo study the genotype–phenotype correlations in patients with GLUD1 mutations. To report the phenotype and functional analysis of a novel mutation (P436L) in the GLUD1 gene associated with the absence of HA.Patients and methodsTwenty patients with HI from 16 families had mutational analysis of the GLUD1 gene in view of HA (n=19) or leucine sensitivity (n=1). Patients negative for a GLUD1 mutation had sequence analysis of the SIRT4 gene. Functional analysis of the novel P436L GLUD1 mutation was performed.ResultsHeterozygous missense mutations were detected in 15 patients with HI/HA, 2 of which are novel (N410D and D451V). In addition, a patient with a normal serum ammonia concentration (21 μmol/l) was heterozygous for a novel missense mutation P436L. Functional analysis of this mutation confirms that it is associated with a loss of GTP inhibition. Seizure disorder was common (43%) in our cohort of patients with a GLUD1 mutation. No mutations in the SIRT4 gene were identified.ConclusionPatients with HI due to mutations in the GLUD1 gene may have normal serum ammonia concentrations. Hence, GLUD1 mutational analysis may be indicated in patients with leucine sensitivity; even in the absence of HA. A high frequency of epilepsy (43%) was observed in our patients with GLUD1 mutations.

We developed a variant database for diabetes syndrome genes, using the Leiden Open Variation Database platform, containing observed phenotypes matched to the genetic variations. We populated it with 628 published disease‐associated variants (December 2016) for: WFS1 (n = 309), CISD2 (n = 3), ALMS1 (n = 268), and SLC19A2 (n = 48) for Wolfram type 1, Wolfram type 2, Alström, and Thiamine‐responsive megaloblastic anemia syndromes, respectively; and included 23 previously unpublished novel germline variants in WFS1 and 17 variants in ALMS1. We then investigated genotype–phenotype relations for the WFS1 gene. The presence of biallelic loss‐of‐function variants predicted Wolfram syndrome defined by insulin‐dependent diabetes and optic atrophy, with a sensitivity of 79% (95% CI 75%–83%) and specificity of 92% (83%–97%). The presence of minor loss‐of‐function variants in WFS1 predicted isolated diabetes, isolated deafness, or isolated congenital cataracts without development of the full syndrome (sensitivity 100% [93%–100%]; specificity 78% [73%–82%]). The ability to provide a prognostic prediction based on genotype will lead to improvements in patient care and counseling. The development of the database as a repository for monogenic diabetes gene variants will allow prognostic predictions for other diabetes syndromes as next‐generation sequencing expands the repertoire of genotypes and phenotypes. The database is publicly available online at https://lovd.euro-wabb.org.

Context: 17α-hydroxylase/17,20-lyase deficiency (17OHD) caused by mutations in the CYP17A1 gene is a rare form of congenital adrenal hyperplasia typically characterized by cortisol deficiency, mineralocorticoid excess and sex steroid deficiency. Objective: To examine the phenotypic spectrum of 17OHD by clinical and biochemical assessment and corresponding in silico and in vitro functional analysis. Design: Case series Patients and Results: We assessed eight patients with 17OHD, including four with extreme 17OHD phenotypes: two siblings presented with failure to thrive in early infancy and two with isolated sex steroid deficiency and normal cortisol reserve. Diagnosis was established by mass spectrometry-based urinary steroid profiling and confirmed by genetic CYP17A1 analysis, revealing homozygous and compound heterozygous sequence variants. We found novel (p.Gly111Val, p.Ala398Glu, p.Ile371Thr), and previously described sequence variants (p.Pro409Leu, p.Arg347His, p.Gly436Arg, p.Phe53/54del, p.Tyr60IlefsLys88X). In vitro functional studies employing an overexpression system in HEK293 cells showed that 17,20-lyase activity was invariably decreased while mutant 17α-hydroxylase activity retained up to 14% of wild-type activity in the two patients with intact cortisol reserve. A ratio of urinary corticosterone over cortisol metabolites reflective of 17α-hydroxylase activity correlated well with clinical phenotype severity. Conclusion: Our findings illustrate the broad phenotypic spectrum of 17OHD. Isolated sex steroid deficiency with normal stimulated cortisol have not been reported before. Attenuation of 17α-hydroxylase activity is readily detected by urinary steroid profiling and predicts phenotype severity.

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Background Clinical neurology has benefitted significantly from advances in molecular genetics with the discovery of disease–associated genes leading to the clinical application of genetic testing. With an ever increasing arsenal of genetic tests available to neurologists we thought it pertinent to review ten years of neurogenetic tests requested by one consultant neurologist focussing in particular on the test outcome and impact on diagnosis. Methods Retrospective data collection using the regional genetics laboratory bank of neurogenetic test requests by one consultant at two acute NHS trusts from February 2002 to February 2012. Clinic letters were used to establish test indication, pre–test working diagnosis, test result, and post–test diagnosis. In addition, data was collected on current test costs from the regional genetics laboratory. Results 137 requests to the regional genetics laboratory in 111 patients with a median age of 45 years (range 16–81 years) were reviewed. Of these requests, 30 (21.9%) were for banking of DNA with 107 (78.1%) for neurogenetic tests in 82 patients. The main indications for neurogenetic testing were: dopa–responsive dystonia (GTP cyclohydrolase) (14 (13.1%)); spinocerebellar ataxia (SCA 1,2,3,6,7) (11 (10.3%)); young–onset Parkinson's disease (PARK2) (8 (7.5%)); young–onset Parkinson's disease (LRRK2) (8 (7.5%)); Friedreich's ataxia (7 (6.5%)), Wilson's disease (ATP7B) (6 (5.6%)) and Leber's hereditary optic neuropathy (6 (5.6%). Of the 107 requests for testing, 22 (20.6%) revealed a genetic abnormality, whilst the vast majority (85 (79.4%)) were normal. Detected genetic abnormalities included: PARK2 (Parkin) mutation (6 (27.3%)); GTP cyclohydrolase mutation (3 (13.6%)); ATP7B mutation (3 (13.6%); Notch–3 mutation (CADASIL) (2 (9.1%)); and reduced chorein (neuroacanthocytosis) (2 (9.1%)). The median cost per test at 2012 prices was £225 (range £95–950). Conclusions Our patient cohort demonstrates that the majority of genetic tests for a broad range of neurological conditions have normal results and do not necessarily add to diagnosis. However, it should be noted that a normal result does not mean a patient hasn't got a genetic cause for their condition, rather that there are many genetic mutations that are not yet fully understood and warrant ongoing research. We propose that in a further ten years' time a similar study would show a greater proportion of genetic mutations with a resultant impact on both diagnosis and management.