John, Peter (2008) GENETIC LINKAGE STUDIES IN ALOPECIAS. PhD thesis, Quaid-i-Azam University, Islamabad .
Alopecia, a generic term for hair loss, results from a diminution of visible hair and there are several forms of hereditary hair loss collectively known as Alopecias. Although hair disorders are not life threatening, their profound impact on social interactions and on patient's psychological well being is undeniable. Genetic conditions affecting hair structure or the hair growth cycle may occur alone or as a part of complex syndromes with associated abnormalities. Several genes have been identified in which underlying mutations produce human hair loss. These genes encode transcription factors, structural proteins and adhesion molecules involved in cell cycling and hair follicle differentiation. The present work involves the study of six Pakistani families (A, B, C, D, E, F) with hereditary hair loss. These families were identified in isolated regions of Pakistan. In family A individuals affected with alopecia and mental retardation (APMR) syndrome, showed total alopecia of scalp and other parts of the body. In addition all the affected individuals were severely mentally retarded. Genome wide scan mapped the first APMR locus on chromosome 3q26.33-q27.3. A maximum two-point LOD score of3.05 (6 = 0) was obtained at marker D3S3583. Multipoint analysis supported linkage to this region with maximum LOD score exceeding 5.0 at several markers. Recombination events observed in affected individuals localized the disease locus between markers D3S1232 and D3S2436, spanning 11.49 cM region on chromosome 3q26.33-q27.3. This region corresponds to a physical map distance of 5.4 Mb. Sequence analysis of the candidate genes ETS variant gene 5 (ETV5) and Phospholipase-H (LIP H) from DNA samples of two affected individuals of the family revealed no mutation. In family B affected individuals showed clinical features of congenital alopecia. Hairs were absent from scalp, with shedding of natal hair shortly after birth. Affected individuals showed no growth or development delay; normal hearing, teeth, nails and no abnormalities in sweating were observed. A genome scan was performed with a panel of 598 microsatellite markers at an average spacing of 5-centimorgan (cM). In the course of this screening, nine genomic regions were found to be homozygous for two to three affected individuals, each of the genomic regions were tested further in four additional family members, however all the regions were excluded and no convincing evidence of linkage was observed. In family C affected individuals exhibited typical clinical features of localized autosomal recessive hypotrichosis (LAH). At birth, hair was present on the scalp, but regrew sparsely after ritual shaving, which is usually performed a week after birth. Affected individuals were nearly devoid of normal eyebrows and eyelashes, however, axillary, pubic and moustache hairs were normal in male affected individuals. Candidate gene mapping showed linkage of this family to micro satellite markers encompassing DSG4 gene at LAH locus on human chromosome 18q12.1. Sequence analysis of the DSG4 gene revealed a recurrent intragenic deletion mutation (Ex5_8del) in the affected individuals of the family. In three families (D, E, F) affected individuals exhibited clinical features of congenital atrichia with papular lesions (APL) including absence of hair from the scalp, axillae, pubic and other parts of the body. Very few keratin-filled follicular cysts were observed on the knees and elbows of all the affected individuals. Candidate gene mapping showed linkage of these families to human hairless gene (HR) at chromosome 8p21. In family D sequence analysis of exon 2 of HR gene revealed a single base pair deletion mutation at position 431 (431 delC) leading to frame shifts and premature termination codon 68 bp downstream in the same exon. In family E, we found a single base pair deletion mutation at position 2021 (2021deIG) in exon 8 of the hairless gene, leading to frame shifts and premature termination codon 959 bp downstream in exon 15. In family F sequences analysis failed to detect a causative mutation. This predicts that mutation may lie in the regulatory region of the hairless gene. The work presented in the thesis has been published in the following articles. 1. John P, Aslam M, Rafiq MA, Amin-ud-din M, Haque S, Ahmad W (2005) Atrichia with papular lesions in two Pakistani consanguineous families resulting from mutations in the human hairless gene. Archives of Dermatological Research 297: 226-230. 2. John P, Ali G, Chishti MS, Naqvi SM, Leal SM, Ahmad W (2006) Localization of a novel locus for alopecia with mental retardation syndrome to chromosome 3q26.33-q27.3. Human Genetics 118: 665-667. 3. John P, Tariq M, Rafiq MA, Amin-ud-din M, Muhammad D, Waheed I, Ansar M, Ahmad W (2006) Recurrent intragenic deletion mutation in desmoglein 4 gene underlies autosomal recessive hypotrichosis in two Pakistani families of Balochi and Sindhi origins. Archives of Dermatological Research 298: 135-137.
|Item Type:||Thesis (PhD)|
|Subjects:||Physical Sciences (f) > Chemistry(f2)|
|Deposited By:||Mr. Javed Memon|
|Deposited On:||08 Jul 2009 10:45|
|Last Modified:||08 Jul 2009 10:45|
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