ABSTRACT
NTNG2 encodes netrin-G2, a membrane-anchored protein implicated in the molecular organization of neuronal circuitry and synaptic organization and diversification in vertebrates. In this study, through a combination of exome sequencing and autozygosity mapping, we have identified 16 individuals (from seven unrelated families) with ultra-rare homozygous missense variants in NTNG2; these individuals present with shared features of a neurodevelopmental disorder consisting of global developmental delay, severe to profound intellectual disability, muscle weakness and abnormal tone, autistic features, behavioral abnormalities, and variable dysmorphisms. The variants disrupt highly conserved residues across the protein. Functional experiments, including in silico analysis of the protein structure, in vitro assessment of cell surface expression, and in vitro knockdown, revealed potential mechanisms of pathogenicity of the variants, including loss of protein function and decreased neurite outgrowth. Our data indicate that appropriate expression of NTNG2 plays an important role in neurotypical development.
Subject(s)
GPI-Linked Proteins/genetics , Mutation, Missense/genetics , Netrins/genetics , Neurodevelopmental Disorders/genetics , Adolescent , Adult , Child , Child, Preschool , Exome/genetics , Female , Homozygote , Humans , Intellectual Disability/genetics , Male , Pedigree , Exome Sequencing/methods , Young AdultABSTRACT
OBJECTIVES: Niemann-Pick diseases (NPD) is an autosomal recessive inherited lysosomal lipid storage disorder which occurs due to a defect in cellular cholesterol trafficking, leading to excess lipid accumulation in multiple organ systems such as the brain, lungs, spleen, and liver. SPMD1-associated disease includes classic infantile and visceral NPD type A and B respectively. Type C NPD is subacute or juvenile. MATERIALS & METHODS: During 2012-2016, the patients who had the clinical and biochemical signs and symptoms of different types of NPD, underwent genetic analysis. All patients were collected from five provinces in Iran (Razavi Khorasan, South Khorasan, Khozaestan, Isfahan and Tehran province). Sanger sequencing of the candidate genes for NPD was performed followed by bioinformatics analysis to confirm the types of NPD and to identify novel mutations. All patients underwent full clinical assessment. RESULTS: We present two cases with NPD type A, six cases with NPD type B, and 11 cases with type C with various enzymatic defects identified in these cases. Within these 19 patients, we present 9 previously reported mutations and 10 novel mutations causing NPD. CONCLUSION: This study is the largest Iranian study for NPD analysis ever. Our report demonstrates that NPD has a variable age of onset and can present early in life. We investigated the clinical and genetic manifestations of a large Iranian cohort. Understanding the variable presentation of NPD will allow for clinicians to have a high index of suspicion for the disease.
