R117H Mutations: Genotype-Phenotype and its Presence in the NBS Panel

1. R117H Mutations: Genotype-Phenotype and its Presence in the NBS Panel I. Bronsveld1, R.A. de Nooijer1, H.G.M. Arets2, F. Teding van Berkhout1, Y. de Rijke3, H.R. de Jonge4. 1Dept. of Pulmonology and 2Dept. of Paediatrics, UMC Utrecht, The Netherlands; 3Dept. of Clinical Chemistry and 4Dept. of Biochemistry, Erasmus MC Rotterdam, The Netherlands. Introduction In spite of the evolving possibilities in CF diagnostic methods and CFTR function tests, in a group of CFTR mutations genotype – phenotype relationships continue to be difficult. Recently, various studies have suggested to categorize the different mutations into groups depending on their possible clinical outcome (Castellani 2008, Farrell 2008). However, mutations such as R117H do not fit in the classification in this manner because of the wide variation in phenotype. In addition, R117H can be found in cis with T5 or T7 which further influence phenotype. NPD Aims To gain further insight into CFTR function and clinical presentation of the R117H mutation. This is especially relevant for a large proportion of persons who tested positive in our newborn screening test by IRT: Until now during neonatal screening using IRT, PAP and DNA analysis we found R117H in 7 out of 18 CF patients (40%), compared to around 1-5% in CF patients diagnosed on clinical grounds. ICM Methods We compared clinical presentation of our homozygous R117H patients. Function tests were performed: nasal potential difference (NPD) and intestinal current measurement (ICM) for CFTR function in the respiratory and intestinal epithelium respectively, sweat test, and fecal elastase to address pancreatic function. Graph 2. NPD and ICM tracing of the R117H homozygous female. NPD: Basal -12mV; Cl-free+Iso -24mV ICM: carb 33.6µA/cm2 Results In our group of 230 paediatric and 150 adult CF patients there were two homozygous R117H (7T/7T) patients, one male (age 35) and one female (age 33). The male patient presented with infertility and appeared to have CBAVD. The female person was only recognised because she underwent CFTR mutation analysis after her son was identified with F508del/R117H by the newborn screening test. She had no clinical symptoms. When measuring NPD in these subjects (Graph 1&2), there was a normal basal PD, amiloride response and total chloride conductance. Cl- secretory responses in ICM upon carbachol addition were within the normal range. Sweat tests in both persons were borderline (Cl- 34 and 42 respectively) and faeces elastases were normal (> 200 μg/g faeces). NPD • Conclusions • R117H homozygosity does not predict clinical presentation • We found: • A male patient: with CBAVD and borderline ST • A female patient: with borderline ST, no other disease phenotype • Therefore, we suggest that R117H is associated with vas deference dysfunction in males, but not with any classical CF symptoms • However, the borderline ST suggests a degree of CFTR dysfunction at least in this organ system • And the presence of two CF mutations including R117H-7T on one allele can be associated with severe lung disease (Peckham et al 2006) • Therefore, it is too early to exclude this mutation from NBS • We will continue our analysis of phenotype and CFTR function tests for insight in the penetration of R117H and the justification of its presence in the NBS panel ICM Graph 1. NPD and ICM tracing of the R117H homozygous male. NPD: Basal -25mV; Cl-free+Iso -11mV ICM: carb 31.9µA/cm2