Nationwide genetic analysis for molecularly unresolved cystic fibrosis patients in a multiethnic society: implications for preconception carrier screening.

BACKGROUND: Preconception carrier screening for cystic fibrosis (CF) is usually performed using ethnically targeted panels of selected mutations. This has been recently challenged by the use of expanded, ethnically indifferent, pan-population panels. Israel is characterized by genetically heterogeneous populations carrying a wide range of CFTR mutations. To assess the potential of expanding the current Israeli preconception screening program, we sought the subset of molecularly unresolved CF patients listed in the Israeli CF data registry comprising ~650 patients. METHODS: An Israeli nationwide genotyping of 152 CF cases, representing 176 patients lacking molecular diagnosis, was conducted. Molecular analysis included Sanger sequencing for all exons and splice sites, multiplex ligation probe amplification (MLPA), and next-generation sequencing of the poly-T/TG tracts. RESULTS: We identified 54 different mutations, of which only 16 overlapped the 22 mutations included in the Israeli preconception screening program. A total of 29/54 (53.7%) mutations were already listed as CF causing by the CFTR2 database, and only 4/54 (7.4%) were novel. Molecular diagnosis was reached in 78/152 (51.3%) cases. Prenatal diagnosis of 24/78 (30.8%) cases could have been achieved by including all CFTR2-causing mutations in the Israeli panel. CONCLUSIONS: Our data reveal an overwhelming hidden abundance of CFTR gene mutations suggesting that expanded preconception carrier screening might achieve higher preconception detection rates.

The impact of a national population carrier screening program on cystic fibrosis birth rate and age at diagnosis: Implications for newborn screening.

BACKGROUND: Population carrier screening (PCS) has been available in Israel since 1999 and universally subsidized since 2008. We sought to evaluate its impact. METHODS: A retrospective review of governmental databanks, the national CF registry and CF centers. RESULTS: CF rate per 100,000 live births has decreased from 14.5 in 1990 to 6 in 2011. From 2004-2011 there were 95 CF births: 22 utilized PCS; 68 (72%) had 2 known CFTR mutations; 37% were pancreatic sufficient. At diagnosis, age was 6 (0-98) months; 53/95 had respiratory symptoms, 41/95 failure to thrive and 19/95 pseudomonas. Thirty-four (36%) were Arabs and 19 (20%) orthodox Jews, compared to 20% and 8% respectively, in the general population. CONCLUSIONS: PCS markedly reduced CF birth rates with a shift towards milder mutations, but was often avoided for cultural reasons. As children regularly have significant disease at diagnosis, we suggest a balanced approach, utilizing both PCS and newborn screening.

Essential role of carbonic anhydrase XII in secretory gland fluid and HCO3 (-) secretion revealed by disease causing human mutation.

KEY POINTS: Fluid and HCO3 (-) secretion is essential for all epithelia; aberrant secretion is associated with several diseases. Carbonic anhydrase XII (CA12) is the key carbonic anhydrase in epithelial fluid and HCO3 (-) secretion and works by activating the ductal Cl(-) -HCO3 (-) exchanger AE2. Delivery of CA12 to salivary glands increases salivation in mice and of the human mutation CA12(E143K) markedly inhibits it. The human mutation CA12(E143K) causes disease due to aberrant CA12 glycosylation, and misfolding resulting in loss of AE2 activity. ABSTRACT: Aberrant epithelial fluid and HCO3 (-) secretion is associated with many diseases. The activity of HCO3 (-) transporters depends of HCO3 (-) availability that is determined by carbonic anhydrases (CAs). Which CAs are essential for epithelial function is unknown. CA12 stands out since the CA12(E143K) mutation causes salt wasting in sweat and dehydration in humans. Here, we report that expression of CA12 and of CA12(E143K) in mice salivary glands respectively increased and prominently inhibited ductal fluid secretion and salivation in vivo. CA12 markedly increases the activity and is the major HCO3 (-) supplier of ductal Cl(-) -HCO3 (-) exchanger AE2, but not of NBCe1-B. The E143K mutation alters CA12 glycosylation at N28 and N80, resulting in retention of the basolateral CA12 in the ER. Knockdown of AE2 and of CA12 inhibited pancreatic and salivary gland ductal AE2 activity and fluid secretion. Accordingly, patients homozygous for the CA12(E143K) mutation have a dry mouth, dry tongue phenotype. These findings reveal an unsuspected prominent role of CA12 in epithelial function, explain the disease and call for caution in the use of CA12 inhibitors in cancer treatment.

Natural history and clinical manifestations of hyponatremia and hyperchlorhidrosis due to carbonic anhydrase XII deficiency.

INTRODUCTION: We identified patients of Bedouin origin with a mutation in carbonic anhydrase XII (CA XII) leading to hyponatremia due to excessive salt loss via sweat. METHODS: The medical records of patients were reviewed for clinical and laboratory data. RESULTS: A total of 11 subjects were identified; 7 symptomatic patients presented with hyponatremic dehydration in infancy. Screening of the entire kindred identified 4 asymptomatic individuals with elevated sweat chloride. All symptomatic patients had failure to thrive and moderate-severe hyponatremia (106-124 mmol·l(-1)); 6 had hypochloremia (79-94 mmol·l(-1)). All asymptomatic subjects had normal or near-normal serum sodium and chloride concentrations. Both symptomatic and asymptomatic subjects had normal renal functions and normal cortisol response on low-dose ACTH test. All symptomatic patients were treated by dietary salt, which prevents episodes of hyponatremic dehydration and promotes growth. At follow-up, the chief complaints remained heat intolerance, accumulation of salt precipitates on the face and hyperhidrosis. No evidence for chronic renal, respiratory, gastrointestinal or fertility abnormalities was found. CONCLUSION: Recognizing this newly described entity and differentiating it from cystic fibrosis and pseudohypoaldosteronism are important. Patients with CA XII mutations should be followed even after early childhood, especially in hot temperatures and intense physical activity.