A novel recessive mutation in the gene ELOVL4 causes a neuro-ichthyotic disorder with variable expressivity
© Mir et al.; licensee BioMed Central Ltd. 2014
Received: 25 December 2012
Accepted: 18 February 2014
Published: 26 February 2014
A rare neuro-ichthyotic disorder characterized by ichthyosis, spastic quadriplegia and intellectual disability and caused by recessive mutations in ELOVL4, encoding elongase-4 protein has recently been described. The objective of the study was to search for sequence variants in the gene ELOVL4 in three affected individuals of a consanguineous Pakistani family exhibiting features of neuro-ichthyotic disorder.
Linkage in the family was searched by genotyping microsatellite markers linked to the gene ELOVL4, mapped at chromosome 6p14.1. Exons and splice junction sites of the gene ELOVL4 were polymerase chain reaction amplified and sequenced in an automated DNA sequencer.
DNA sequence analysis revealed a novel homozygous nonsense mutation (c.78C > G; p.Tyr26*).
Our report further confirms the recently described ELOVL4-related neuro-ichthyosis and shows that the neurological phenotype can be absent in some individuals.
KeywordsIchthyosis Phenotypic variability ELOVL4 Non-sense mutation
Elongation of Very Long chain fatty acids-4 (ELOVL4) is a member of a large family of fatty acid elongases (ELO), involved in biosynthesis of very long-chain fatty acid (VLCFAs) with chain length ≥24 carbon atoms. Fatty acid elongases add two-carbon extensions to existing fatty acid substrates to generate longer chained fatty acids . Seven members of the ELOVL family (ELOVL1-7) have been identified in humans that differ from each other in their substrate specificity, tissue expression and developmental patterns [2–4]. These can be divided into two major groups including ELOVL1, 3, 6 and 7, which are suggested to be elongases of saturated and monounsaturated VLCFA and ELOVL2 and 5, which are involved in the elongation of polyunsaturated fatty acids (PUFA) . It has been identified that ELOVL4 is active both in the elongation of saturated VLCFA and in the biosynthesis of polyunsaturated VLC-PUFA .
It was first identified that heterozygous mutations in the gene ELOVL4 are responsible for a dominant form of Stargardt-like macular dystrophy (STGD3) . Patients with heterozygous ELOVL4 mutations exhibit macular degeneration, which is probably related to a deficiency of VLCFA-containing lipids in the retina . Recently, Aldahmesh et al.  have shown recessive mutations in the gene ELOVL4 in two children causing congenital ichthyosis, along with a profound neurological phenotype and spastic quadriplegia.
In the present study we have investigated a consanguineous Pakistani family displaying an autosomal recessive neuroichthyotic disorder. Genotyping using microsatellite markers showed linkage of the family to the gene ELOVL4, mapped on chromosome 6q14. Subsequently, sequence analysis of the gene revealed a novel homozygous nonsense mutation (p.Tyr26*).
Genomic DNA was extracted from peripheral blood samples collected from three affected and three unaffected members of the family by GenElute™ blood genomic DNA kit (Sigma-Aldrich, St. Louis, MO, USA). A skin biopsy was performed and the sample was fixed in 10% formalin and embedded in paraffin. Four-μm-thick sections were stained with hematoxylin-eosin.
The family was tested for linkage by genotyping microsatellite markers linked to genes involved in neuro-ichthyotic syndromes. These include Aldehyde Dehyrogenase 3A2 gene (ALDH3A2, MIM 270200) on chromosome 17p11 (D17S261, D17S1857, D17S1794, D17S805, D17S842, D17S783, D17S1878), involved in Sjögren-Larsson Syndrome (SLS), and Elongase-4 gene (ELOVL4, MIM 605512) on chromosome 6p14.1 (D6S1659, D6S1031, D6S286, D6S251, D6S391, D6S1609, D6S1627). Order of markers was based on Rutgers combined linkage-physical map of the human genome .
Standard sequence of the gene ELOVL4 was obtained from Ensembl Genome Browser (http://asia.ensembl.org/index.html). Primers for PCR (polymease chain reaction) amplification of all six exons and splice junction sites of the gene were designed using Primer3 version 0.4.0 software . DNA sequencing was performed with Big Dye Terminator v3.1 Cycle Sequencing Kit, together with an ABI Prism 310 Genetic Analyzer (Applera, Foster City, CA, USA). Sequence variants were identified via Bioedit sequence alignment tool (editor version 6.0.7, Ibis, Biosciences, CA, USA).
All three affected individuals (IV-1, IV-2, IV-5) of the family, presented here, showed typical features of the hereditary ichthyosis. Skin in all the affected individuals was dry, erythematous and hyperkeratotic with scales present on lips, tip of the nose, ear pinna, legs, matacarpophalangeal joints and feet (Figure 1b-e). In individual IV-2, who died recently, back and neck were also affected. Intellectual disability and spastic quadriplegia were observed only in patient IV-2. He was born by normal vaginal delivery at home, but develops fever accompanied by frequent urination at 4 months of age. Profound developmental delay and occurrence of seizures were reported, a year after birth. Seizures were occurring very frequently mostly at twenty minutes time interval. Severe hypertonia developed in the upper and lower extremities in this individual. Bones and muscles appeared extremely weak. Speech and hearing were abnormal. He remained bed ridden until he died. Oral examination showed leukoplakia with white patches appeared on tongue. Significant dental erosion involving second incisor and canine were observed.
Skin biopsy of the affected individual IV-1 showed hyperkeratosis and acanthosis of the epidermis, edema of the basal layer of epidermis causing its disruption and leading to the formation of sub epidermal cleft formation (Figure 1). Sparse lymphocytic cellular infiltrate scattered in the dermis mainly around the blood vessels was noted.
In all the three affected individuals ichthyosis was present since birth. In cold weather, this condition turns to more severe form which develops itching and pain in the affected areas. Prominent ears with large pinna and yellow pigmented nails were observed in all the affected individuals.
Magnetic resonance imaging (MRI) and computed tomography (CT) scan images of the affected individuals were not available for the study. History of cardiac, diabetic and immunological problems was not reported in any of the affected individuals. Obligate heterozygous carriers in the family were normal and were clinically indistinguishable from genotypically normal individuals.
Linkage and mutation analysis
In the present investigation, we have reported clinical and molecular analysis of a consanguineous Pakistani family presenting clinical manifestations of a neuro-ichthyotic syndrome. Intra-familial phenotypic variability was observed among affected individuals of the family. Characteristic features of ichthyosis affecting different parts of the body were observed in all three affected individuals. However, other features including intellectual disability, hypertonia and spastic quadriplegia linked to the neuro-ichthyotic syndrome were observed only in one affected individual of the family. This individual died recently. Similar features were reported in two individuals with a neuro-ichthyotic syndrome by Aldahmesh et al. . Clinical features including leukoplakia, prominent ears with large pinna and yellow pigmented nails, observed with variable severity, in affected individuals of the present family were not reported earlier. Other features like inguinal hernias, small testicular size, and microcephaly reported by Aldahmesh et al. , were not observed in affected members of our family.
Genotyping using microsatellite marker established linkage in the family to the gene ELOVL4 on chromosome 6p14.1. Sequence analysis of the gene revealed a novel homozygous nonsense mutation (p.Tyr26*) in all three affected individuals. To date, two recessive mutations (p.Arg216*, p.Ile230Metfs*22) causing a neuro-ichthyotic syndrome  and three heterozygous mutations (p.Asn264Thrfs*10, p.Asn264Leufs*9, p.Tyr270*) causing Stargardt-like macular degeneration [6, 11–13] have been reported in the gene ELOVL4.
The gene ELOVL4, containing six coding exons, spans 32.7 kb of genomic DNA and encode 314 amino acids protein. The ELOVL4 contains five membrane-spanning domains, a histidine cluster motif (HXXHH) involved in enzymatic activity, and endoplasmic reticulum retention signal composed of a di-lysine motif (KXKXX) at the C-terminus (Figure 3b). All the previous mutations reported in the gene ELOVL4 were clustered in the C terminus of the protein. The novel mutation (p.Tyr26*), identified in the present study, is the only mutation located at N-terminus of the protein. This mutation is predicted to result in loss of function of the ELOVL4 protein either through nonsense mediated mRNA decay or production of a truncated protein. In the latter case, the truncated protein product lacks five transmemrane domains, a histidine cluster and a dilysine-motif. It is highly likely that the mutant ELOVL4 protein carrying the nonsense mutation (p.Tyr26*) may lack the elongase activity required for synthesis of very-long-chain fatty acids (VLCFAs) in skin and brain, and results in the abnormal localization of the protein as well.
In this study we have reported only the third recessive mutation in the gene ELOVL4 causing neuro-ichthyotic syndrome. Interestingly, analysis revealed the same mutation resulted in appearance of neurological phenotype only in one of the three affected individuals of the same family. As ELOVL4 is involved in the elongation of C26 to C28 VLCFAs, that are important components of retinal, skin and brain phospholipids and sphingolipids [1, 2], any change in the structure and stability of ELOVL4 protein may alter this pathway of VLCFAs biosynthesis. One of the possible factors contributing towards phenotypic variability, observed in the three affected individuals, is alternative use of at least one of the eleven in-frame ATG codons downstream of the mutation site.
Elongation of very long chain fatty acids-4
Very-long-chain fatty acids
Polyunsaturated fatty acids
Stargardt-like macular dystrophy type-3
Institutional Review Board
Aldehyde Dehyrogenase 3A2 gene
Mendelian inheritance in man
Polymease chain reaction
Magnetic resonance imaging
Computed tomography scan.
We highly appreciate invaluable cooperation and participation of the family members in the present study. This work was financially supported by Higher Education Commission (HEC), Islamabad, Pakistan. Hina Mir was supported by indigenous PhD fellowship from HEC, Islamabad, Pakistan.
- Leonard AE, Bobbi EG, Dorado J, Kroeger PE, Chuang LT, Thurmond JM, Parker-Barnes JM, Das T, Huang YS, Mukerji P: Cloning of a human cDNA encoding a novel enzyme involved in the elongation of long-chain polyunsaturated fatty acids. Biochem J. 2000, 350: 765-770. 10.1042/0264-6021:3500765.View ArticlePubMedPubMed CentralGoogle Scholar
- Jakobsson A, Westerberg R, Jacobsson A: Fatty acid elongases in mammals: their regulation and roles in metabolism. Prog Lipid Res. 2006, 45: 237-249. 10.1016/j.plipres.2006.01.004.View ArticlePubMedGoogle Scholar
- Tamura K, Makino A, Hullin-Matsuda F, Kobayashi T, Furihata M, Chung S, Ashida S, Miki T, Fujioka T, Shuin T, Nakamura Y, Nakagawa H: Novel lipogenic enzyme ELOVL7 is involved in prostate cancer growth through saturated long-chain fatty acid metabolism. Cancer Res. 2009, 69: 8133-8140. 10.1158/0008-5472.CAN-09-0775.View ArticlePubMedGoogle Scholar
- Leonard AE, Pereira SL, Sprecher H, Huang YS: Elongation of long-chain fatty acids. Prog Lipid Res. 2004, 43: 36-54. 10.1016/S0163-7827(03)00040-7.View ArticlePubMedGoogle Scholar
- Agbaga MP, Brush RS, Mandal MN, Henry K, Elliott MH, Anderson RE: Role of Stargardt-3 macular dystrophy protein (ELOVL4) in the biosynthesis of very long chain fatty acids. Proc Natl Acad Sci USA. 2008, 105: 12843-12848. 10.1073/pnas.0802607105.View ArticlePubMedPubMed CentralGoogle Scholar
- Zhang K, Kniazeva M, Han M, Li W, Yu Z, Yang Z, Li Y, Metzker ML, Allikmets R, Zack DJ, Kakuk LE, Lagali PS, Wong PW, MacDonald IM, Sieving PA, Figueroa DJ, Austin CP, Gould RJ, Ayyagari R, Petrukhin K: A 5-bp deletion in ELOVL4 is associated with two related forms of autosomal dominant macular dystrophy. Nat Genet. 2001, 27: 89-93.PubMedGoogle Scholar
- Vasireddy V, Wong P, Ayyagari R: Genetics and molecular pathology of Stargardt-like macular degeneration. Prog Retin Eye Res. 2010, 29: 191-207. 10.1016/j.preteyeres.2010.01.001.View ArticlePubMedPubMed CentralGoogle Scholar
- Aldahmesh MA, Mohamed JY, Alkuraya HS, Verma IC, Puri RD, Alaiya AA, Rizzo WB, Alkuraya FS: Recessive mutations in ELOVL4 cause ichthyosis, intellectual disability, and spastic quadriplegia. Am J Hum Genet. 2011, 89: 745-750. 10.1016/j.ajhg.2011.10.011.View ArticlePubMedPubMed CentralGoogle Scholar
- Matise TC, Chen F, Chen W, De La Vega FM, Hansen M, He C, Hyland FC, Kennedy GC, Kong X, Murray SS, Ziegle JS, Stewart WC, Buyske S: A second-generation combined linkage physical map of the human genome. Genome Res. 2007, 17: 1783-1786. 10.1101/gr.7156307.View ArticlePubMedPubMed CentralGoogle Scholar
- Rozen S, Skaletsky H: Primer3 on the WWW for general users and for biologist programmers. Methods Mol Biol. 2000, 132: 365-386.PubMedGoogle Scholar
- Edwards AO, Donoso LA, Ritter R: A novel gene for autosomal dominant Stargardt-like macular dystrophy with homology to the SUR4 protein family. Invest Ophthalmol Vis Sci. 2001, 42: 2652-2663.PubMedGoogle Scholar
- Bernstein PS, Tammur J, Singh N, Hutchinson A, Dixon M, Pappas CM, Zabriskie NA, Zhang K, Petrukhin K, Leppert M, Allikmets R: Diverse macular dystrophy phenotype caused by a novel complex mutation in the ELOVL4 gene. Invest Ophthalmol Vis Sci. 2001, 42: 3331-3336.PubMedGoogle Scholar
- Maugeri A, Meire F, Hoyng CB, Vink C, Van Regemorter N, Karan G, Yang Z, Cremers FP, Zhang K: A novel mutation in the ELOVL4 gene causes autosomal dominant Stargardt-like macular dystrophy. Invest Ophthalmol Vis Sci. 2004, 45: 4263-4267. 10.1167/iovs.04-0078.View ArticlePubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2350/15/25/prepub
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.