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Case 2. 13 day old patient (AEO) referred through the NNS programme (November 2007) Raised IRT level; Tested for deltaF508, G551D, G542X and 621+1G>T panel; Single copy of deltaF508 identified; No other mutations identified on full screen.

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case 2
Case 2
  • 13 day old patient (AEO) referred through the NNS programme (November 2007)
      • Raised IRT level;
      • Tested for deltaF508, G551D, G542X and 621+1G>T panel;
      • Single copy of deltaF508 identified;
      • No other mutations identified on full screen
  • Parents of AEO (EO & CO) referred for carrier testing (January 2008);
      • EO - deltaF508 heterozygote;
      • No mutation detected in CO

INTERPRETATION

DNA extracted from a bloodspot from AEO has been tested for the 28 cystic fibrosis mutations listed below.

A single copy of the c.1521_1523delCTT mutation (traditionally known as deltaF508) has been identified.

The test will identify approximately 80% of CF mutations in the North East population. This means that approximately 32% of affected CF individuals will have a single detectable mutation by this test.

INTERPRETATION

EO and CO have been tested for the 28 cystic fibrosis mutations listed below.

A single copy of the c.1521_1523delCTT mutation (traditionally known as deltaF508) has been identified in EO.

This confirms EO is a carrier of cystic fibrosis.

No mutations were identified in CO. This test will identify approximately 80% of CF mutations in the North East population.

The interpretation of this result depends on whether a clinical diagnosis of cystic fibrosis has been confirmed in AEO, as we cannot exclude CO from being a carrier of a rare mutation not detected by this test.

case 21
Case 2
  • Cascade screening (1):
      • AEO’s paternal uncle and his wife are referred for carrier testing (GO & SO);
      • SO pregnant at time of referral
      • GO - deltaF508 heterozygote
      • SO - R117H (7T / 7T)

INTERPRETATION

GO and SO have been tested for the 28 cystic fibrosis mutations listed below.

A single copy of the c.1521_1523delCTT mutation (traditionally known as deltaF508) has been identified in GO.

A single copy of the c.350G>A mutation (traditionally known as R117H) has been identified in SO.

SO has also been tested for an intron 8 polymorphism and found to be homozygous for the 7T allele. The c.350G>A mutation when found in conjunctions with the 7T allele is predicted to act as a mild cystic fibrosis mutation.

This confirms that both GO and SO are carriers of cystic fibrosis.

GO’s and SO’s risk of having a child affected with cystic fibrosis-related symptoms is therefore 1 in 4 although the c.350G>A mutation in combination with the c.1521_1523delCTT is not necessarily associated with classical CF.

  • Pre-natal diagnosis:
      • Amniotic fluid sample taken from SO’s current pregnancy received for CF testing;
      • Compound heterozygote for deltaF508 / R117H
  • Cascade screening (2):
      • Anxious to know the CF status of apparently healthy 2 year old daughter;
      • ZO referred for CF testing (December 2007);
      • ZO - compound heterozygote for deltaF508 / R117H

INTERPRETATION

DNA extracted from the amniotic fluid sample from SO (taken on xxx) has been tested for the 28 cystic fibrosis mutations listed below. Compound heterozygosity for the cystic fibrosis mutations, c.1521_1523delCTT and c.350G>A (traditionally known as R117H) has been detected.

From this result we would therefore predict the outcome of this pregnancy to be a child affected with cystic fibrosis, although the c.350G>A mutation in combination with c.1521_1523delCTT is not necessarily associated with classical CF.

DNA extracted from the amnio and maternal blood samples have been tested for 15 polymorphic marker loci spread throughout the genome, plus the amelogenin locus. There is no significant evidence for maternal cell contamination of the amnio sample.

INTERPRETATION

ZO is a compound heterozygote for the cystic fibrosis mutations, c.1521_1523delCTT and c.350G>A (traditionally known as deltaF508 and R117H.

ZO is therefore at high risk of developing cystic fibrosis-related symptoms, although the c.350G>A mutation (especially on a 7T background) in combination with c.1521_1523delCTT is not necessarily associated with classical CF.

case 22
Case 2

Discussion Points

  • Emmanuelle Girodon : study of the French newborn screening programme suggests that all their R117H cases are 7T associated. What’s more, in trans with a CF mutation such as F508del, they are asymptomatic.
  • In the States (Garry Cutting), R117H(T7) is not reported, as it is considered not to be associated with disease.
  • It is certainly true that if you look at all cases of R117H(T7), however ascertained (i.e. not just through CF clinics), you find that the penetrance of the mutation is low: maybe only 10-15% are associated with disease.
  • ? Time to review what we say in our R117H(T7) reports..
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