Vahidnezhad, Hassan

ABSTRACT Nicotinamide adenine dinucleotide phosphate hydrate dehydratase (NAXD) and nicotinamide adenine dinucleotide phosphate hydrate epimerase (NAXE) deficiencies are rare autosomal recessive metabolic disorders characterized by severe neurological manifestations during infancy. In affected individuals, febrile illnesses can trigger progressive encephalopathy often accompanied by distinctive skin eruptions, resulting in high mortality rates. This study reviews the literature on NAXD/NAXE deficiencies, focusing on dermatological manifestations and their correlation with genotypic variations and treatment responses. A comprehensive literature search identified 45 patients with 31 pathogenic/likely pathogenic mutations, and a median age of onset at 1.16 years. Patients with NAXE deficiency exhibited a broader range of age of symptom onset compared to those affected with NAXD deficiency. Fever or infections were identified as the most common triggers for decompensation episodes. Skin manifestations were observed in 31% of patients with whole cell NAXD and NAXE deficiencies. The characteristic skin eruption comprises well‐demarcated erythematous and erosive plaques progressing to blistering and necrosis, predominantly affecting flexural surfaces. The mortality rate was 78%, with survivors experiencing varying degrees of neurological sequelae. Niacin/nicotinamide supplementation resulted in improvements in skin lesions and survival rates. The review underscores the critical role of dermatologists in early diagnosis and intervention of NAXE and NAXD deficiencies. Recognizing characteristic skin manifestations is essential, particularly in patients with acute neurological decline following infections or vaccinations. Early intervention with specific supplements shows promise; however, further research is needed to establish standardized treatment protocols and enhance patient outcomes.

Abstract Background Among the approximately 8000 Mendelian disorders, >1000 have cutaneous manifestations. In many of these conditions, the underlying mutated genes have been identified by DNA-based techniques which, however, can overlook certain types of mutations, such as exonic-synonymous and deep-intronic sequence variants. Whole-transcriptome sequencing by RNA sequencing (RNA-seq) can identify such mutations and provide information about their consequences. Methods We analyzed the whole transcriptome of 40 families with different types of Mendelian skin disorders with extensive genetic heterogeneity. The RNA-seq data were examined for variant detection and prioritization, pathogenicity confirmation, RNA expression profiling, and genome-wide homozygosity mapping in the case of consanguineous families. Among the families examined, RNA-seq was able to provide information complementary to DNA-based analyses for exonic and intronic sequence variants with aberrant splicing. In addition, we tested the possibility of using RNA-seq as the first-tier strategy for unbiased genome-wide mutation screening without information from DNA analysis. Results We found pathogenic mutations in 35 families (88%) with RNA-seq in combination with other next-generation sequencing methods, and we successfully prioritized variants and found the culprit genes. In addition, as a novel concept, we propose a pipeline that increases the yield of variant calling from RNA-seq by concurrent use of genome and transcriptome references in parallel. Conclusions Our results suggest that “clinical RNA-seq” could serve as a primary approach for mutation detection in inherited diseases, particularly in consanguineous families, provided that tissues and cells expressing the relevant genes are available for analysis.