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Loss of NPC1 function in a patient with a co-inherited novel insulin receptor mutation does not grossly modify the severity of the associated insulin resistance.

Kirk J, Porter KM, Parker V, Barroso I, O'Rahilly S, Hendriksz C, Semple RK - J. Inherit. Metab. Dis. (2010)

Bottom Line: INSR mRNA and protein levels were normal in dermal fibroblasts, consistent with a primary signal transduction defect in the mutant receptor.Although the proband was significantly more insulin resistant than her father, who carried the INSR mutation but was only heterozygous for the NPC1 variant, their respective degrees of IR were very similar to those previously reported in a father-daughter pair with the closely related p.Trp1193Leu INSR mutation.This suggests that loss of NPC1 function, with attendant changes in membrane cholesterol composition, does not significantly modify the IR phenotype, even in the context of severely impaired INSR function.

View Article: PubMed Central - PubMed

Affiliation: Department of Endocrinology, Birmingham Children's Hospital, Steelhouse Lane, Birmingham B4 6NH, United Kingdom.

ABSTRACT
In Npc1 mice, a model for Niemann Pick Disease Type C1, it has been reported that hepatocyte insulin receptor function is significantly impaired, consistent with growing evidence that membrane fluidity and microdomain structure have an important role in insulin signal transduction. However, whether insulin receptor function is also compromised in human Niemann Pick disease Type C1 is unclear. We now report a girl who developed progressive dementia, ataxia and opthalmoplegia from 9 years old, followed by severe acanthosis nigricans, hirsutism and acne at 11 years old. She was diagnosed with Niemann Pick Disease type C1 (OMIM#257220) based on positive filipin staining and reduced cholesterol-esterifying activity in dermal fibroblasts, and homozygosity for the p.Ile1061Thr NPC1 mutation. Further analysis revealed her also to be heterozygous for a novel trinucleotide deletion (c.3659 + 1_3659 + 3delGTG) at the end of exon 20 of INSR, encoding the insulin receptor, leading to deletion of Trp1193 in the intracellular tyrosine kinase domain. INSR mRNA and protein levels were normal in dermal fibroblasts, consistent with a primary signal transduction defect in the mutant receptor. Although the proband was significantly more insulin resistant than her father, who carried the INSR mutation but was only heterozygous for the NPC1 variant, their respective degrees of IR were very similar to those previously reported in a father-daughter pair with the closely related p.Trp1193Leu INSR mutation. This suggests that loss of NPC1 function, with attendant changes in membrane cholesterol composition, does not significantly modify the IR phenotype, even in the context of severely impaired INSR function.

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Related in: MedlinePlus

The Proband has a heterozygous GTG deletion at the end of exon 20 of the INSR gene in genomic DNA (a), which is seen also in INSR cDNA (b). The nucleotide deletion causes deletion of Trp1220 (Trp1193 in the mature receptor), a strongly conserved residue (c) located in an alpha helix within the tyrosine kinase damin of the receptor. There was no detectable change in expression of the INSR in dermal fibroblasts from the proband as assessed by quantitative real time PCR (d) and immunoprecipitation/immunoblotting (e) for the insulin receptor beta subunit
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Fig1: The Proband has a heterozygous GTG deletion at the end of exon 20 of the INSR gene in genomic DNA (a), which is seen also in INSR cDNA (b). The nucleotide deletion causes deletion of Trp1220 (Trp1193 in the mature receptor), a strongly conserved residue (c) located in an alpha helix within the tyrosine kinase damin of the receptor. There was no detectable change in expression of the INSR in dermal fibroblasts from the proband as assessed by quantitative real time PCR (d) and immunoprecipitation/immunoblotting (e) for the insulin receptor beta subunit

Mentions: Further sequencing of genomic DNA revealed heterozygosity for the previously unreported deletion of one of a pair of trinucleotides around the end of exon 20 of the INSR gene (GenBank NM_000208; c.3659 + 1_3659 + 3delGTG) (Fig. 1a). Sequencing of cDNA from dermal fibroblasts confirmed heterozygous deletion of this trinuceotide also in the cDNA (Fig. 1b), leading to deletion of the highly conserved Tryptophan 1193 from the mature receptor (Fig. 1c). Quantitative real time PCR and immunoprecipitation/immunoblotting showed no reduction in INSR expression in dermal fibroblasts from the proband compared to controls (Fig. 1d, e).Fig. 1


Loss of NPC1 function in a patient with a co-inherited novel insulin receptor mutation does not grossly modify the severity of the associated insulin resistance.

Kirk J, Porter KM, Parker V, Barroso I, O'Rahilly S, Hendriksz C, Semple RK - J. Inherit. Metab. Dis. (2010)

The Proband has a heterozygous GTG deletion at the end of exon 20 of the INSR gene in genomic DNA (a), which is seen also in INSR cDNA (b). The nucleotide deletion causes deletion of Trp1220 (Trp1193 in the mature receptor), a strongly conserved residue (c) located in an alpha helix within the tyrosine kinase damin of the receptor. There was no detectable change in expression of the INSR in dermal fibroblasts from the proband as assessed by quantitative real time PCR (d) and immunoprecipitation/immunoblotting (e) for the insulin receptor beta subunit
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3757264&req=5

Fig1: The Proband has a heterozygous GTG deletion at the end of exon 20 of the INSR gene in genomic DNA (a), which is seen also in INSR cDNA (b). The nucleotide deletion causes deletion of Trp1220 (Trp1193 in the mature receptor), a strongly conserved residue (c) located in an alpha helix within the tyrosine kinase damin of the receptor. There was no detectable change in expression of the INSR in dermal fibroblasts from the proband as assessed by quantitative real time PCR (d) and immunoprecipitation/immunoblotting (e) for the insulin receptor beta subunit
Mentions: Further sequencing of genomic DNA revealed heterozygosity for the previously unreported deletion of one of a pair of trinucleotides around the end of exon 20 of the INSR gene (GenBank NM_000208; c.3659 + 1_3659 + 3delGTG) (Fig. 1a). Sequencing of cDNA from dermal fibroblasts confirmed heterozygous deletion of this trinuceotide also in the cDNA (Fig. 1b), leading to deletion of the highly conserved Tryptophan 1193 from the mature receptor (Fig. 1c). Quantitative real time PCR and immunoprecipitation/immunoblotting showed no reduction in INSR expression in dermal fibroblasts from the proband compared to controls (Fig. 1d, e).Fig. 1

Bottom Line: INSR mRNA and protein levels were normal in dermal fibroblasts, consistent with a primary signal transduction defect in the mutant receptor.Although the proband was significantly more insulin resistant than her father, who carried the INSR mutation but was only heterozygous for the NPC1 variant, their respective degrees of IR were very similar to those previously reported in a father-daughter pair with the closely related p.Trp1193Leu INSR mutation.This suggests that loss of NPC1 function, with attendant changes in membrane cholesterol composition, does not significantly modify the IR phenotype, even in the context of severely impaired INSR function.

View Article: PubMed Central - PubMed

Affiliation: Department of Endocrinology, Birmingham Children's Hospital, Steelhouse Lane, Birmingham B4 6NH, United Kingdom.

ABSTRACT
In Npc1 mice, a model for Niemann Pick Disease Type C1, it has been reported that hepatocyte insulin receptor function is significantly impaired, consistent with growing evidence that membrane fluidity and microdomain structure have an important role in insulin signal transduction. However, whether insulin receptor function is also compromised in human Niemann Pick disease Type C1 is unclear. We now report a girl who developed progressive dementia, ataxia and opthalmoplegia from 9 years old, followed by severe acanthosis nigricans, hirsutism and acne at 11 years old. She was diagnosed with Niemann Pick Disease type C1 (OMIM#257220) based on positive filipin staining and reduced cholesterol-esterifying activity in dermal fibroblasts, and homozygosity for the p.Ile1061Thr NPC1 mutation. Further analysis revealed her also to be heterozygous for a novel trinucleotide deletion (c.3659 + 1_3659 + 3delGTG) at the end of exon 20 of INSR, encoding the insulin receptor, leading to deletion of Trp1193 in the intracellular tyrosine kinase domain. INSR mRNA and protein levels were normal in dermal fibroblasts, consistent with a primary signal transduction defect in the mutant receptor. Although the proband was significantly more insulin resistant than her father, who carried the INSR mutation but was only heterozygous for the NPC1 variant, their respective degrees of IR were very similar to those previously reported in a father-daughter pair with the closely related p.Trp1193Leu INSR mutation. This suggests that loss of NPC1 function, with attendant changes in membrane cholesterol composition, does not significantly modify the IR phenotype, even in the context of severely impaired INSR function.

Show MeSH
Related in: MedlinePlus