RESUMEN
Most people with cystic fibrosis (CF) are diagnosed following abnormal newborn screening (NBS), which begins with measurement of immunoreactive trypsinogen (IRT) values. A case report found low concentrations of IRT in an infant with CF exposed to the CF transmembrane conductance regulator (CFTR) modulator, elexacaftor-tezacaftor-ivacaftor (ETI), in utero. However, IRT values in infants born to mothers taking ETI have not been systematically assessed. We hypothesized that ETI-exposed infants have lower IRT values than newborns with CF, CFTR-related metabolic syndrome/CF screen positive, inconclusive diagnosis (CRMS/CFSPID), or CF carriers. IRT values were collected from infants born in Indiana between 1 January 2020, and 2 June 2022, with ≥1 CFTR mutation. IRT values were compared to infants born to mothers with CF taking ETI followed at our institution. Compared to infants identified with CF (n = 51), CRMS/CFSPID (n = 21), and CF carriers (n = 489), ETI-exposed infants (n = 19) had lower IRT values (p < 0.001). Infants with normal NBS results for CF had similar median (interquartile range) IRT values, 22.5 (16.8, 30.6) ng/mL, as ETI-exposed infants, 18.9 (15.2, 26.5). IRT values from ETI-exposed infants were lower than for infants with abnormal NBS for CF. We recommend that NBS programs consider performing CFTR variant analysis for all ETI-exposed infants.
RESUMEN
Cystic fibrosis (CF) is an autosomal recessive disorder characterized by the accumulation of sticky and heavy mucus that can damage several organs. CF shows variable expressivity in affected individuals, but it typically causes respiratory and digestive complications as well as congenital bilateral absence of the vas deferens in males. Individuals with classic CF usually have variants that produce a defective protein from both alleles of the CFTR gene. Individuals with other variants may present with classic, non-classic, or milder forms of CF due to lower levels of functional CFTR protein. This article reports the genetic analysis of a female with features of asthma and mild or non-classic CF. CFTR sequencing demonstrated that she is a carrier for a maternally derived 5T/12TG variant. Deletion/duplication analysis by multiplex ligation-dependent probe amplification (MLPA) showed the presence of an intragenic paternally derived duplication involving exons 7-11 of the CFTR gene. This duplication is predicted to result in the production of a truncated CFTR protein lacking the terminal part of the nucleotide-binding domain 1 (NBD1) and thus is likely to be a non-functioning allele. The combination of this large intragenic duplication and 5T/12TG is the probable cause of the mild or non-classic CF features in this individual.
