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      An ABCD1 Mutation (c.253dupC) Caused Diverse Phenotypes of Adrenoleukodystrophy in an Iranian Consanguineous Pedigree

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          Abstract

          Objectives

          Current study was the first to report a consanguineous Iranian pedigree with ABCD1 mutation.

          Methods

          Targeted molecular analysis was initially performed in three affected individuals in one family suspected to have X-ALD due to chronic progressive spasticity. Upon confirmation of genetic diagnosis, further neurologic and genetic evaluation of all family members was done.

          Results

          A mutation in ABCD1 was identified in 35 affected individuals (out 96 pedigree members). The c. 253dup, in exon 1, leads to a frame shift and a premature stop codon at amino acid position 194 (p.Arg85Profs*110). Surprisingly, affected individuals in our cohort show some variability in phenotype, including childhood cerebral ALD, adrenomyeloneuropathy, and addison-only disease phenotypes, expanding the phenotype of X-ALD with p.Arg85Profs*110.

          Conclusion

          This report characterizes the clinical spectrum of an expanded Iranian pedigree with X-ALD due to an ABCD1 mutation. Given a high frequency of carriers in this region, we expect the prevalence of X-ALD to be higher, underscoring the importance of genetic counseling through reliable identification of heterozygous as well as homozygote females in consanguineous communities.

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          Most cited references38

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          Putative X-linked adrenoleukodystrophy gene shares unexpected homology with ABC transporters.

          Adrenoleukodystrophy (ALD) is an X-linked disease affecting 1/20,000 males either as cerebral ALD in childhood or as adrenomyeloneuropathy (AMN) in adults. Childhood ALD is the more severe form, with onset of neurological symptoms between 5-12 years of age. Central nervous system demyelination progresses rapidly and death occurs within a few years. AMN is a milder form of the disease with onset at 15-30 years of age and a more progressive course. Adrenal insufficiency (Addison's disease) may remain the only clinical manifestation of ALD. The principal biochemical abnormality of ALD is the accumulation of very-long-chain fatty acids (VLCFA) because of impaired beta-oxidation in peroxisomes. The normal oxidation of VLCFA-CoA in patients' fibroblasts suggested that the gene coding for the VLCFA-CoA synthetase could be a candidate gene for ALD. Here we use positional cloning to identify a gene partially deleted in 6 of 85 independent patients with ALD. In familial cases, the deletions segregated with the disease. An identical deletion was detected in two brothers presenting with different clinical ALD phenotypes. Candidate exons were identified by computer analysis of genomic sequences and used to isolate complementary DNAs by exon connection and screening of cDNA libraries. The deduced protein sequence shows significant sequence identity to a peroxisomal membrane protein of M(r) 70K that is involved in peroxisome biogenesis and belongs to the 'ATP-binding cassette' superfamily of transporters.
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            Nonsense-mediated decay approaches the clinic.

            Nonsense-mediated decay (NMD) eliminates mRNAs containing premature termination codons and thus helps limit the synthesis of abnormal proteins. New results uncover a broader role of NMD as a pathway that also affects the expression of wild-type genes and alternative-splice products. Because the mechanisms by which NMD operates have received much attention, we discuss here the emerging awareness of the impact of NMD on the manifestation of human genetic diseases. We explore how an understanding of NMD accounts for phenotypic differences in diseases caused by premature termination codons. Specifically, we consider how the protective function of NMD sometimes benefits heterozygous carriers and, in contrast, sometimes contributes to a clinical picture of protein deficiency by inhibiting expression of partially functional proteins. Potential 'NMD therapeutics' will therefore need to strike a balance between the general physiological benefits of NMD and its detrimental effects in cases of specific genetic mutations.
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              ABCD1 mutations and the X-linked adrenoleukodystrophy mutation database: role in diagnosis and clinical correlations.

              X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene, which encodes a peroxisomal ABC half-transporter (ALDP) involved in the import of very long-chain fatty acids (VLCFA) into the peroxisome. The disease is characterized by a striking and unpredictable variation in phenotypic expression. Phenotypes include the rapidly progressive childhood cerebral form (CCALD), the milder adult form, adrenomyeloneuropathy (AMN), and variants without neurologic involvement. There is no apparent correlation between genotype and phenotype. In males, unambiguous diagnosis can be achieved by demonstration of elevated levels of VLCFA in plasma. In 15 to 20% of obligate heterozygotes, however, test results are false-negative. Therefore, mutation analysis is the only reliable method for the identification of heterozygotes. Since most X-ALD kindreds have a unique mutation, a great number of mutations have been identified in the ABCD1 gene in the last seven years. In order to catalog and facilitate the analysis of these mutations, we have established a mutation database for X-ALD ( http://www.x-ald.nl). In this review we report a detailed analysis of all 406 X-ALD mutations currently included in the database. Also, we present 47 novel mutations. In addition, we review the various X-ALD phenotypes, the different diagnostic tools, and the need for extended family screening for the identification of new patients. Copyright 2001 Wiley-Liss, Inc.
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                Author and article information

                Journal
                101256516
                35703
                J Mol Genet Med
                J Mol Genet Med
                Journal of molecular and genetic medicine : an international journal of biomedical research
                1747-0862
                26 July 2016
                19 June 2016
                June 2016
                01 August 2016
                : 10
                : 2
                : 222
                Affiliations
                [1 ]Department of Neurology, Firoozgar Hospital, Iran University of medical sciences (IUMS), Tehran, Iran
                [2 ]Medical Student Research Committee (MSRC), Faculty of Medicine, Iran University of medical sciences (IUMS), Tehran, Iran
                [3 ]Department of Medical Genetics, School of Medicine, Tehran University of Medical Sciences (TUMS), Tehran, Iran
                [4 ]Department of Medical Genetics and Molecular Biology, Faculty of Medicine, Iran University of Medical Sciences (IUMS), Tehran, Iran
                [5 ]NIH Undiagnosed Diseases Program, National Human Genome Research Institute (NHGRI), National Institutes of Health, Bethesda, Maryland, USA
                Author notes
                [* ]Corresponding author: Babak Behnam, NIH Undiagnosed Diseases Program, National Human Genome Research Institute (NHGRI), National Institute of Health (NIH), Bethesda, MD 20892, USA, Tel: 3015945182; Fax: 3014800804; Babak.Behnam@ 123456nih.gov
                Article
                NIHMS805161
                10.4172/1747-0862.1000222
                4969076
                27489563
                252e9a90-1e30-4ffc-8220-ca6b96d6b9d0

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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                Categories
                Article

                Molecular medicine
                abcd1,adrenoleukodystrophy,x-linked,mutation
                Molecular medicine
                abcd1, adrenoleukodystrophy, x-linked, mutation

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