Genotype and functional correlates of disease phenotype in deficiency of adenosine deaminase 2 (DADA2)

BACKGROUND Deficiency of adenosine deaminase 2 (DADA2) is a syndrome with pleiotropic manifestations including vasculitis and hematologic compromise. A systematic definition of the relationship between ADA2 mutations and clinical phenotype remains unavailable. OBJECTIVE We tested whether the impact of ADA2 mutations on enzyme function correlates with clinical presentation. METHODS DADA2 patients with severe hematologic manifestations were compared with vasculitis-predominant patients. Enzymatic activity was assessed using expression constructs reflecting all 53 missense, nonsense, insertion and deletion genotypes from 152 patients across the DADA2 spectrum. RESULTS We identified DADA2 patients presenting with pure red cell aplasia (PRCA, n = 5) or bone marrow failure syndrome (BMF, n = 10). Most patients did not exhibit features of vasculitis. Recurrent infection, hepatosplenomegaly and gingivitis were common in patients with BMF, of whom half died from infection. Unlike DADA2 patients with vasculitis, patients with PRCA and BMF proved largely refractory to tumor necrosis factor inhibitors. ADA2 variants associated with vasculitis predominantly reflected missense mutations with at least 3% residual enzymatic activity. By contrast, PRCA and BMF were associated with missense mutations with minimal residual enzyme activity, nonsense variants, and insertions / deletions resulting in complete loss of function. CONCLUSION Functional interrogation of ADA2 mutations reveals an association of subtotal function loss with vasculitis, typically responsive to TNF blockade, whereas more extensive loss is observed in hematologic disease which may be refractory to treatment. These findings establish a genotype-phenotype spectrum in DADA2

Adolescent nonalcoholic fatty liver disease and type 2 diabetes in young adulthood.

CONTEXT: The long-term risk of type 2 diabetes in adolescents with nonalcoholic fatty liver disease (NAFLD) is unclear. OBJECTIVE: To assess type 2 diabetes risk among adolescents with NAFLD. DESIGN AND SETTING: A nationwide, population-based study of Israeli adolescents who were examined before military service during 1997-2011 and were followed until December 31, 2016. PARTICIPANTS: A total of 1,025,796 normoglycemic adolescents were included. INTERVENTIONS: Biopsy or radiographic tests were prerequisite for NAFLD diagnosis. Data were linked to the Israeli National Diabetes Registry. MAIN OUTCOME MEASURES: Type 2 diabetes incidence. RESULTS: During a mean follow-up of 13.3 years, 12 of 633 adolescents with NAFLD (1.9%; all with high BMI at baseline) were diagnosed with type 2 diabetes as compared to 2,917 (0.3%) adolescents without NAFLD. The hazard ratio (HR) for type 2 diabetes was 2.59 (95% CI 1.47-4.58) for the NAFLD vs. the non-NAFLD group after adjustment for BMI and socio-demographic confounders. The elevated risk persisted in several sensitivity analyses. These included an analysis of persons without other metabolic comorbidities (adjusted HR 2.75 [95% CI 1.48-5.14]) and of persons with high BMI; and an analysis whose outcome was type 2 diabetes by age 30 years (adjusted HR 2.14 [95% CI 1.02-4.52]). The results remained significant when a sex-, birth year- and BMI-matched control group was the reference (adjusted HR 2.98 [95% CI 1.54-5.74]). CONCLUSIONS: Among normoglycemic adolescents, NAFLD was associated with an increased adjusted risk for type 2 diabetes, which may be apparent before age 30 years

Mutations in PPCS, encoding phosphopantothenoylcysteine synthetase, cause autosomal-recessive dilated cardiomyopathy.

Coenzyme A (CoA) is an essential metabolic cofactor used by around 4% of cellular enzymes. Its role is to carry and transfer acetyl and acyl groups to other molecules. Cells can synthesize CoA de novo from vitamin B5 (pantothenate) through five consecutive enzymatic steps. Phosphopantothenoylcysteine synthetase (PPCS) catalyzes the second step of the pathway during which phosphopantothenate reacts with ATP and cysteine to form phosphopantothenoylcysteine. Inborn errors of CoA biosynthesis have been implicated in neurodegeneration with brain iron accumulation (NBIA), a group of rare neurological disorders characterized by accumulation of iron in the basal ganglia and progressive neurodegeneration. Exome sequencing in five individuals from two unrelated families presenting with dilated cardiomyopathy revealed biallelic mutations in PPCS, linking CoA synthesis with a cardiac phenotype. Studies in yeast and fruit flies confirmed the pathogenicity of identified mutations. Biochemical analysis revealed a decrease in CoA levels in fibroblasts of all affected individuals. CoA biosynthesis can occur with pantethine as a source independent from PPCS, suggesting pantethine as targeted treatment for the affected individuals still alive

Characterization of T and B cell repertoire diversity in patients with RAG deficiency

Recombination-activating genes 1 and 2 (RAG1 and RAG2) play a critical role in T and B cell development by initiating the recombination process that controls the expression of T cell receptor (TCR) and immunoglobulin genes. Mutations in the RAG1 and RAG2 genes in humans cause a broad spectrum of phenotypes, including severe combined immunodeficiency (SCID) with lack of T and B cells, Omenn syndrome, leaky SCID, and combined immunodeficiency with granulomas or autoimmunity (CID-G/AI). Using next-generation sequencing, we analyzed the TCR and B cell receptor (BCR) repertoire in 12 patients with RAG mutations presenting with Omenn syndrome (n = 5), leaky SCID (n = 3), or CID-G/AI (n = 4). Restriction of repertoire diversity skewed usage of variable (V), diversity (D), and joining (J) segment genes, and abnormalities of CDR3 length distribution were progressively more prominent in patients with a more severe phenotype. Skewed usage of V, D, and J segment genes was present also within unique sequences, indicating a primary restriction of repertoire. Patients with Omenn syndrome had a high proportion of class-switched immunoglobulin heavy chain transcripts and increased somatic hypermutation rate, suggesting in vivo activation of these B cells. These data provide a framework to better understand the phenotypic heterogeneity of RAG deficiency

Mutations in PPCS, Encoding Phosphopantothenoylcysteine Synthetase, Cause Autosomal-Recessive Dilated Cardiomyopathy

Coenzyme A (CoA) is an essential metabolic cofactor used by around 4% of cellular enzymes. Its role is to carry and transfer acetyl and acyl groups to other molecules. Cells can synthesize CoA de novo from vitamin B5 (pantothenate) through five consecutive enzymatic steps. Phosphopantothenoylcysteine synthetase (PPCS) catalyzes the second step of the pathway during which phosphopantothenate reacts with ATP and cysteine to form phosphopantothenoylcysteine. Inborn errors of CoA biosynthesis have been implicated in neurodegeneration with brain iron accumulation (NBIA), a group of rare neurological disorders characterized by accumulation of iron in the basal ganglia and progressive neurodegeneration. Exome sequencing in five individuals from two unrelated families presenting with dilated cardiomyopathy revealed biallelic mutations in PPCS, linking CoA synthesis with a cardiac phenotype. Studies in yeast and fruit flies confirmed the pathogenicity of identified mutations. Biochemical analysis revealed a decrease in CoA levels in fibroblasts of all affected individuals. CoA biosynthesis can occur with pantethine as a source independent from PPCS, suggesting pantethine as targeted treatment for the affected individuals still alive