Categories of ΔF508 homozygous cystic fibrosis twin and sibling pairs with distinct phenotypic characteristics

Abstract

Cysti c fi br osi s (CF), the most common sever e autosomal r ecessi ve tr ai t among Caucasi ans, i s caused by mol ecul ar l esi ons i n the cysti c fi br osi s tr ansmembr ane conductance r egul ator gene (CFTR). The cour se of the mul ti -or gan di sease CF i s hi ghl y var i abl e, suggesti ng the i nfl uence of envi r onmental factor s and/or modul ati ng genes other than CFTR on the di sease phenotype. To evaluate the cause of CF disease variability, the European CF Twin and Sibling Study col l ected data on tw o cl i ni cal par ameter s most sensi ti ve for the cour se and pr ognosi s of CF, i e w ei ght pr edi cted for hei ght (w fh)% (r epr esentati ve for the nutr i ti onal status) and FEVPer c (r epr esentati ve for the pul monar y status) for a cohor t of 277 si bl i ng pai r s, 12 pai r s of di zygous tw i ns and 29 pai r s of monozygous tw i ns. Of these 318 CF tw i n and si b pai r s, 114 w er e r epor ted to be homozygous for the most fr equent CF di sease-causi ng l esi on, ∆F508. I ntr a-pai r di scor dance w as assessed by the i ntr a-pai r di ffer ences w i th w fh% and FEVPer c and by DELTA , a composi te par ameter defi ned by l i near combi nati on of w fh% and FEVPer c i n or der to descr i be di scor dance w i th r espect to the overall disease severity. Monozygous twins had a significantly lower DELTA than dizygous twins (P = 0.05) i ndi cati ng that CF di sease sever i ty i s modul ated by an i nher i ted component i n addi ti on to the CFTR gene i tsel f. Extr eme phenotypes ar e consi der ed to be mor e i nfor mati ve for the anal ysi s of any quanti tati ve tr ai t. Thus, w e ai med to quanti fy di sease sever i ty and i ntr a-pai r di scor dance i n or der to sel ect pai r s w i th the extr eme phenotypes DI S (di scor dant pati ent pai r s), CON + (concor dant and mi l dy affected pati ent pai r s) and CON -(concor dant and sever el y affected pati ent pairs). The algorithm reliably discriminated between pairs DIS, CON + and CON -among the cohor t of ∆F508 homozygotes. The sel ected pai r s fr om these categor i es demonstr ated non-over l appi ng pr oper ti es for w fh%, FEVPer c and the i ntr a-pai r di ffer ence of both par ameter s. Twin Research (2000) 3, 277-293. Keyw or ds: cysti c fi brosi s di sease severi ty, affected rel ati ve pai r, tw i n and si bl i ng study, extreme phenotypes, al gori thm based sel ecti on I ntr oducti on Cysti c fi brosi s (CF) i s know n as the most common severe autosomal recessi ve di sease w i thi n the Caucasi an popul ati on, exhi bi ti ng an i nci dence of 1 i n 2500 bi rths.1 The symptoms of the di sorder are caused by an i mpai red functi on of exocri ne gl ands i n many organs, but major mani festati ons i nvol ve the respi ratory and the gastroi ntesti nal tracts.1 The di sease i s caused by mutati ons i n both chromosomal copi es of the cysti c fi brosi s transmembrane conductance regul ator (CFTR) gene. 2 The course of CF i s hi ghl y vari abl e w hen compari ng unrel ated pati ents w i th i denti cal CFTR mutati on genotypes, 3,4 o...

Genetic Modifiers of Liver Disease in Cystic Fibrosis

“…Initial Study. Of the 158 patients with CF evaluated for CFLD (enrolled January 1999-December 2004), 128 fulfilled criteria from 22 CF centers in 10 countries (Australia [8], Canada [17], Czech Republic [17], Germany [3], Italy [28], the Netherlands [1], Scotland [2], Slovakia [4], Turkey [4], and United States [44]). For patients without 2 defined mutations in CFTR, we performed further testing using a panel of 70 mutations (CFTR mutation detection assay; Tm Bioscience/Luminex, Austin, Texas).…”

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TAS2R38 is a novel modifier gene in patients with cystic fibrosis

“…The clinical manifestation of cystic fibrosis (CF) is highly heterogeneous also depending on the functional effect of the CFTR genotype 1,2 . However, patients with the same CFTR genotype may display a clinical discordance 3 and a percentage of sibling pairs affected by CF display a discordant clinical manifestation 3,4 reinforcing the concept that complex alleles (i.e., additional mutations on the same allele 5 ), non-coding regions of CFTR 6,7 or other genes, inherited independently of CFTR, modulate the clinical manifestation and complications of patients with CF 8 . Patients with CF frequently show different degrees of chronic rhinosinusitis 9,10 with poor perception of sinonasal symptoms 11 and pulmonary colonization by Pseudomonas aeruginosa and other opportunistic bacteria 12,13 .…”