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Mutation R117H Overview
R117H is a mutation that is known to be affected by intragenic modification (see
Glossary 
). By itself, R117H does not act as a CF-causing mutation. However, under certain circumstances, (and – as always – when
another CF-causing mutation is present), R117H can cause disease.
Whether or not R117H causes disease is based on another region of the CFTR gene
called the poly-T tract. The poly-T tract is present in every copy of the CFTR gene and occurs in one of three
forms: 5T, 7T, or 9T. Depending on which poly-T form is present in the same copy of the CFTR gene with R117H,
differing outcomes may occur. These possible combinations and their outcomes are listed in the table below.
Please note: In order to correctly interpret the table, it is necessary to know the phase of the
mutations. The phase refers to the specific combination of mutations that are present together in the same copy
of the CFTR gene. For instance, a patient may have the following mutations: R117H/G551D and 5T/7T. Determining
the phase means determining which poly-T variation (5T or 7T) is in the same copy of the CFTR gene as R117H and
which is in the same copy as G551D. For some patients, testing of their parents is necessary to determine the
phase of the mutations.
| One mutation: | Second mutation: R117H + ? | Predicted outcome: |
|---|
| CF-causing mutation, such as F508del |
R117H and 5T |
R117H will likely act as a disease-causing mutation. Most patients with this combination of mutations
and the 5T form of the poly-T tract will have elevated sweat chloride and clinical symptoms of CF. Symptoms
for these patients may be variable. There is an increased risk for male infertility. |
| CF-causing mutation, such as F508del |
R117H and 7T |
R117H is unlikely to act as a disease-causing mutation (particularly for females), but may result in male infertility.
However, a person with this combination of mutations and this form of the poly-T tract may have borderline or elevated sweat
chloride and mild clinical symptoms of CF. |
| CF-causing mutation, such as F508del |
R117H and 9T |
R117H is highly unlikely to act as a disease-causing mutation. The vast majority of individuals will not
have CF. Male fertility is typically not affected by R117H and 9T. |
This page was last updated on 12/08/2011
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Permitted use available to clinicians, patients, and family members for clinical, research, and educational uses only. All other rights reserved.
@ Copyright 2011 US CF Foundation, Johns Hopkins University, The Hospital for Sick Children. |
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