Genetic modifiers of nutritional status in cystic fibrosis

Arteriovenous metabolomics in pigs reveals CFTR regulation of metabolism in multiple organs

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF), a multiorgan disease that is characterized by diverse metabolic defects. However, other than specific CFTR mutations, the factors that influence disease progression and severity remain poorly understood. Aberrant metabolite levels have been reported, but whether CFTR loss itself or secondary abnormalities (infection, inflammation, malnutrition, and various treatments) drive metabolic defects is uncertain. Here, we implemented comprehensive arteriovenous metabolomics in newborn CF pigs, and the results revealed CFTR as a bona fide regulator of metabolism. CFTR loss impaired metabolite exchange across organs, including disruption of lung uptake of fatty acids, yet enhancement of uptake of arachidonic acid, a precursor of proinflammatory cytokines. CFTR loss also impaired kidney reabsorption of amino acids and lactate and abolished renal glucose homeostasis. These and additional unexpected metabolic defects prior to disease manifestations reveal a fundamental role for CFTR in controlling multiorgan metabolism. Such discovery informs a basic understanding of CF, provides a foundation for future investigation, and has implications for developing therapies targeting only a single tissue.

Disparities in first evaluation of infants with cystic fibrosis since implementation of newborn screening

OBJECTIVE

We evaluated whether implementation of cystic fibrosis (CF) newborn screening (NBS) leads to equitable timeliness of initial evaluation. We compared age at first event (AFE, age at sweat test, encounter and/or care episode) between infants categorized as Black/African American, American Indian/ Native Alaskan, Asian, and/or Hispanic and/or other (Group 1) to White and not Hispanic infants (Group 2).

METHODS

This retrospective cohort study from the Cystic Fibrosis Foundation Patient Registry (CFFPR) included infants born 2010-2018. Race and ethnicity categories followed US Census definitions. The primary outcome was AFE; the secondary outcome was weight for age (WFA) z-score averaged 12 to < 24 months. We compared distributions by Wilcoxon rank-sum test and proportions by Chi-square or Fisher's exact tests. A nested cohort study used a linear mixed effects model of variables that affect WFA, chosen a priori, to evaluate associations with 1-year WFA z-score.

RESULTS

Among 6354 infants, 21% were in Group 1. Group 1 median AFE was 31 days (IQR 19, 49) and Group 2 was 22 days (IQR 14,36) (p< .001). Median WFA z-score at 1-2 years was lower in Group 1. In 3017 infants with complete data on variables of interest, AFE, Black race, CFTR variant class I-III, prematurity and public insurance were associated with lower 1-year WFA z-score.

CONCLUSIONS

Differences in AFE for infants with CF from historically marginalized groups may exacerbate long standing health disparities. We speculate that inequitable identification of CFTR gene variants and/or bias may influence timeliness of evaluation after an out-of-range NBS.

Mutation profiling of the c.1521_1523delCTT (p.Phe508del, F508del) CFTR allele using haplotype-resolved long-read next generation sequencing

Current approaches to characterize the mutational profile of the cystic fibrosis transmembrane conductance regulator (CFTR) gene are based on targeted mutation analysis (TMA) or whole gene studies derived from short-read next generation sequencing (NGS). However, these methods lack phasing capability which, in certain scenarios, can provide clinically valuable information. In the present work, we performed near-full length CFTR using Single-Molecule Real-Time Sequencing to produce haplotype-resolved data from both homozygous and heterozygous individuals for mutation c.1521_1523delCTT (p.Phe508del, F508del). This approach utilizes target enrichment of the CFTR gene using biotinylated probes, facilitates multiplexing samples in the same sequencing run, and utilizes fully-automated bioinformatics pipelines for error correction and variant calling. We show a remarkable conservation of F508del haplotype, consistent with the single gene founder effect, as well as diverse mutational profiles in non-F508del alleles. By the same method, 105 single nucleotide polymorphisms (SNPs) exhibiting invariant linkage to F508del CFTR (which better define the founder haplotype) were identified. High level homology between F508del sequences derived from heterozygotes, and those obtained from homozygous individuals, demonstrate accuracy of this method to produce haplotype resolved sequencing. The studies provide a new diagnostic technology for detailed analysis of complex CFTR alleles linked to disease severity. This article is protected by copyright. All rights reserved.

Assessment of Cystic Fibrosis Distribution Based on Air Pollution by Geographical Information System (GIS)

BACKGROUND

It is widely accepted that concerns have been recently raised regarding the impact of air pollution on the health of children with cystic fibrosis (CF). Air pollution probably affects the exacerbation of CF and its laboratory findings. On the other hand, the World Health Organization (WHO) has asked all countries to update their data and reports on the distribution and prevalence of CF in different areas. The purpose of the present study was to investigate the distribution and prevalence of CF based on the levels of atmospheric pollutants, such as PM₁₀, PM_2.5, SO₂, NO₂, CO, and O₃ in 22 zones of Tehran, and to report the abnormal laboratory findings that might indicate the exacerbation of CF.

MATERIALS AND METHODS

The studied statistical population included children with CF referred to Masih Daneshvari Hospital from 2003 to 2020. Demographic data, location of living area, and laboratory findings were extracted from patient records. The geographic information system (GIS) was applied to indicate the distribution and dispersion of the disease. The information related to air pollutants was collected from all stations in Tehran during the studied period by the Department of Environment of Tehran Province, and the average levels were used for final reporting.

RESULTS

The analysis results on 287 CF patients demonstrated that the risk of disease exacerbation significantly increased by the presence of air pollutants. In areas with multiple air pollutants, more laboratory findings were observed to be abnormal, and the lower survival rate for patients with CF was recorded. Investigating the CF distribution pattern based on climatic layers and above mean sea level (AMSL) indicated that distribution of the disease was higher in dry areas with lower AMSL and the higher volume of the atmospheric pollutants, which were primarily centralized in southern and central Tehran.

CONCLUSION

Environmental factors, such as air pollution, can be considered vital parameters, along with high-risk factors, such as pure and integrated race, migration, and mutation, influencing the prevalence and exacerbation of CF symptoms. Considering the higher prevalence of CF in deprived areas of Tehran, households' cultural and economic level appears to be a factor in the lack of diagnostic screening and prevention of CF in these areas. On the other hand, continuous monitoring of the air pollution caused by traffic and giving warnings to CF patients and their parents is particularly important.

Standards of Nutritional Care for Patients with Cystic Fibrosis: A Methodological Primer and AGREE II Analysis of Guidelines

Although many Clinical Practice Guidelines (CPGs) have been published for the care of patients with Cystic Fibrosis (CF), including a variety of nutrition recommendations, the quality of these CPGs has never been evaluated. The aim of this study was to compare, review, and critically appraise CPGs for the nutritional management of CF, throughout the lifespan. We searched PubMed, Guidelines International Network (GIN), ECRI Institute, and Guidelines Central for CPGs, with information on the nutritional management of CF. Retrieved CPGs were appraised by three independent reviewers, using the Appraisal of Guidelines, Research and Evaluation II (AGREE II) instrument and checklist. A total of 22 CPGs (seven solely nutrition oriented), by 14 different publishers, were retrieved. The Thoracic Society of Australia and New Zealand CPGs scored the highest overall quality (94.4%), while the Paediatric Gastroenterology Society/Dietitians Association of Australia CPGs had the lowest score (27.8%). Great variation in AGREE II domain-specific scores was observed in all CPGs, suggesting the existence of different strengths and weaknesses. Despite the availability of several CPGs, many appear outdated, lacking rigor, transparency, applicability, and efficiency, while incorporating bias. Considering that CPGs adherence is associated with better outcomes and the need for improving life expectancy in patients with CF, the development of CPGs of better quality is deemed necessary.

Genetic Modifying Factors of Cystic Fibrosis Phenotype: A Challenge for Modern Medicine

Cystic fibrosis (CF) is a monogenic autosomal recessive disease caused by cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations. CF is characterized by a high phenotypic variability present even in patients with the same genotype. This is due to the intervention of modifier genes that interact with both the CFTR gene and environmental factors. The purpose of this review is to highlight the role of non-CFTR genetic factors (modifier genes) that contribute to phenotypic variability in CF. We analyzed literature data starting with candidate gene studies and continuing with extensive studies, such as genome-wide association studies (GWAS) and whole exome sequencing (WES). The results of both types of studies revealed that the number of modifier genes in CF patients is impressive. Their identification offers a new perspective on the pathophysiological mechanisms of the disease, paving the way for the understanding of other genetic disorders. In conclusion, in the future, genetic analysis, such as GWAS and WES, should be performed routinely. A challenge for future research is to integrate their results in the process of developing new classes of drugs, with a goal to improve the prognosis, increase life expectancy, and enhance quality of life among CF patients.

Tensin 1 (TNS1) is a modifier gene for low body mass index (BMI) in homozygous [F508del]CFTR patients

Cystic fibrosis (CF) is a life‐limiting autosomal recessive genetic disease caused by variants in the CFTR gene, most commonly by the [F508del] variant. Although CF is a classical Mendelian disease, genetic variants in several modifier genes have been associated with variation of the clinical phenotype for pulmonary and gastrointestinal function and urogenital development. We hypothesized that whole genome sequencing of a well‐phenotyped CF populations might identify novel variants in known, or hitherto unknown, modifier genes. Whole genome sequencing was performed on the Illumina HiSeq X platform for 98 clinically diagnosed cystic fibrosis patient samples from the Adult CF Clinic at the University of California San Diego (UCSD). We compared protein‐coding, non‐silent variants genome wide between CFTR [F508del] homozygotes vs CFTR compound heterozygotes. Based on a single variant score test, we found 3 SNPs in common variants (MAF >5%) that occurred at significantly different rates between homozygous [F508del]CFTR and compound heterozygous [F508del]CFTR patients. The 3 SNPs were all located in one gene on chromosome 2: Tensin 1 (TNS1: rs3796028; rs2571445: and rs918949). We observed significantly lower BMIs in homozygous [F508del]CFTR patients who were also homozygous for Tensin 1 rs918949 (T/T) (p = 0.023) or rs2571445 (G/G) (p = 0.02) variants. The Tensin 1 gene is thus a potential modifier gene for low BMI in CF patients homozygous for the [F508del]CFTR variant.

Forskolin-induced swelling of intestinal organoids correlates with disease severity in adults with cystic fibrosis and homozygous F508del mutations

BACKGROUND

CFTR function measurements in intestinal organoids may help to better characterise individual disease expression in F508del homozygous people. Our objective was to study correlations between CFTR function as measured with forskolin-induced swelling in rectal organoids with clinical parameters in adult patients with homozygous F508del mutations.

METHODS

Multicentre observational study. Thirty-four adults underwent rectal biopsy, pulmonary function tests (FEV₁ and FVC), chest X-ray and chest CT. Body-mass index (BMI) was assessed at study visit and exacerbation rate was determined during five years prior to study visit. Organoids were cultured and measured after stimulation with 5 µm forskolin for three hours to quantitate CFTR residual function.

FINDINGS

FIS was positively correlated with FEV₁ (r = 0.36, 95% CI 0.02-0.62, p = 0.04) and BMI (r = 0.42, 95% CI 0.09-0.66, p = 0.015). FIS was negatively correlated with PRAGMA-CF CT score for% of disease (r = -0.37, 95% CI -0.62- -0.03, p = 0.049). We found no significant correlation between FIS and chest radiography score for CF (r = -0.16, 95% CI -0.48-0.20, p = 0.44). We observed a trend between higher FIS and a lower mean number of exacerbations over the last 5 years of observation, but this was not statistically significant (Poisson regression, p = 0.089).

INTERPRETATION

FIS of intestinal organoids varied between subjects with homozygous F508del and correlated with pulmonary and nutritional parameters. These findings suggest that differences at low CFTR residual function may contribute to clinical heterogeneity in F508del homozygous patients and small changes in CFTR residual function might impact long-term disease expression.

Disease-modifying genetic factors in cystic fibrosis

PURPOSE OF REVIEW

To compile data from the past 10 years regarding the role of modifying genes in cystic fibrosis (CF).

RECENT FINDINGS

CF is a model disease for understanding of the action of modifying genes. Although it is a monogenic (CFTR) autosomal recessive disease, CF presents with wide phenotypic variability. In CF, variability occurs with different intensity among patients by each organ, being organ-specific, resulting from the mutual interaction of environmental and genetic factors, including CFTR mutations and various other genes, most of which are associated with inflammatory processes. In individuals, using precision medicine, gene modification studies have revealed individualized responses to drugs depending on particular CFTR mutations and modifying genes, most of which are alternative ion channels.

SUMMARY

Studies of modifying genes in CF allow: understanding of clinical variability among patients with the same CFTR genotype; evaluation of precision medicine; understanding of environmental and genetic effects at the organ level; understanding the involvement of genetic variants in inflammatory responses; improvements in genetic counseling; understanding the involvement of genetic variants in inflammatory responses in lung diseases, such as asthma; and understanding the individuality of the person with the disease.

Cystic Fibrosis Disease Modifiers: Complex Genetics Defines the Phenotypic Diversity in a Monogenic Disease

In many respects, genetic studies in cystic fibrosis (CF) serve as a paradigm for a human Mendelian genetic success story. From recognition of the condition as a heritable pathological entity to implementation of personalized treatments based on genetic findings, this multistep pathway of progress has focused on the genetic underpinnings of CF clinical disease. Along this path was the recognition that not all CFTR gene mutations produce the same disease and the recognition of the complex, multifactorial nature of CF genotype–phenotype relationships. The non- CFTR genetic components (gene modifiers) that contribute to variation in phenotype are the focus of this review. A multifaceted approach involving candidate gene studies, genome-wide association studies, and gene expression studies has revealed significant gene modifiers for multiple CF phenotypes. The bold challenges for the future are to integrate the findings into our understanding of CF pathogenesis and to use the knowledge to develop novel therapies.

Cystic fibrosis in the era of precision medicine

The treatment of people with cystic fibrosis (CF) has been transformed by the availability of drugs that target the basic chloride defect in the disease. The use of drugs that target specific molecular defects embodies the goals of precision medicine, which incorporate preventive and therapeutic strategies and takes into account differences among individuals. However, the entirety of CF care, from diagnosis to understanding the clinical phenotype and developing a therapeutic strategy, depends on taking into account individual characteristics to achieve optimal outcomes. Future therapies are likely to be even more individualized ushering in a new era of precision medicine.

Update of literature from cystic fibrosis registries 2012-2015. Part 6: Epidemiology, nutrition and complications

Patient registries provide useful information to afford more knowledge on rare diseases like Cystic Fibrosis (CF). Twenty-two studies originating from national CF registries, focusing on demographics, survival, genetics, nutritional status, and non-pulmonary complications, were published between December 2011 and March 2015. The purpose of this review article is to examine these reports, aiming attention to the clinical characteristics of CF patients included in the registries, current, and estimated future epidemiological data, the role of gender gap, the increasing survival in different countries. Some studies offer insights into pubertal growth and non-pulmonary complications, such as liver disease, nephropathy, and cancer. Pediatr Pulmonol. 2017;52:390-398. © 2016 Wiley Periodicals, Inc.

Sources of Variation in Sweat Chloride Measurements in Cystic Fibrosis

RATIONALE

Expanding the use of cystic fibrosis transmembrane conductance regulator (CFTR) potentiators and correctors for the treatment of cystic fibrosis (CF) requires precise and accurate biomarkers. Sweat chloride concentration provides an in vivo assessment of CFTR function, but it is unknown the degree to which CFTR mutations account for sweat chloride variation.

OBJECTIVES

To estimate potential sources of variation for sweat chloride measurements, including demographic factors, testing variability, recording biases, and CFTR genotype itself.

METHODS

A total of 2,639 sweat chloride measurements were obtained in 1,761 twins/siblings from the CF Twin-Sibling Study, French CF Modifier Gene Study, and Canadian Consortium for Genetic Studies. Variance component estimation was performed by nested mixed modeling.

MEASUREMENTS AND MAIN RESULTS

Across the tested CF population as a whole, CFTR gene mutations were found to be the primary determinant of sweat chloride variability (56.1% of variation) with contributions from variation over time (e.g., factors related to testing on different days; 13.8%), environmental factors (e.g., climate, family diet; 13.5%), other residual factors (e.g., test variability; 9.9%), and unique individual factors (e.g., modifier genes, unique exposures; 6.8%) (likelihood ratio test, P < 0.001). Twin analysis suggested that modifier genes did not play a significant role because the heritability estimate was negligible (H2 = 0; 95% confidence interval, 0.0-0.35). For an individual with CF, variation in sweat chloride was primarily caused by variation over time (58.1%) with the remainder attributable to residual/random factors (41.9%).

CONCLUSIONS

Variation in the CFTR gene is the predominant cause of sweat chloride variation; most of the non-CFTR variation is caused by testing variability and unique environmental factors. If test precision and accuracy can be improved, sweat chloride measurement could be a valuable biomarker for assessing response to therapies directed at mutant CFTR.

ESPEN-ESPGHAN-ECFS guidelines on nutrition care for infants, children, and adults with cystic fibrosis

BACKGROUND

Malnutrition is both a frequent feature and a comorbidity of cystic fibrosis (CF), with nutritional status strongly associated with pulmonary function and survival. Nutritional management is therefore standard of care in CF patients. ESPEN, ESPGHAN and ECFS recommended guidelines to cover nutritional management of patients with CF.

METHODS

The guidelines were developed by an international multidisciplinary working group in accordance with officially accepted standards. The GRADE system was used for determining grades of evidence and strength of recommendation. Statements were discussed, submitted to Delphi rounds, reviewed by ESPGHAN and ECFS and accepted in an online survey among ESPEN members.

RESULTS

The Working Group recommends that initiation of nutritional management should begin as early as possible after diagnosis, with subsequent regular follow up and patient/family education. Exclusive breast feeding is recommended but if not possible a regular formula is to be used. Energy intake should be adapted to achieve normal weight and height for age. When indicated, pancreatic enzyme and fat soluble vitamin treatment should be introduced early and monitored regularly. Pancreatic sufficient patients should have an annual assessment including fecal pancreatic elastase measurement. Sodium supplementation is recommended and a urinary sodium:creatinine ratio should be measured, corresponding to the fractional excretion of sodium. If iron deficiency is suspected, the underlying inflammation should be addressed. Glucose tolerance testing should be introduced at 10 years of age. Bone mineral density examination should be performed from age 8-10 years. Oral nutritional supplements followed by polymeric enteral tube feeding are recommended when growth or nutritional status is impaired. Zinc supplementation may be considered according to the clinical situation. Further studies are required before essential fatty acids, anti-osteoporotic agents, growth hormone, appetite stimulants and probiotics can be recommended.

CONCLUSION

Nutritional care and support should be an integral part of management of CF. Obtaining a normal growth pattern in children and maintaining an adequate nutritional status in adults are major goals of multidisciplinary cystic fibrosis centers.

Diagnosis of Adult Patients with Cystic Fibrosis

The diagnosis of cystic fibrosis (CF) is being made with increasing frequency in adults. Patients with CF diagnosed in adulthood typically present with respiratory complaints, and often have recurrent or chronic airway infection. At the time of initial presentation individuals may appear to have clinical manifestation limited to a single organ, but with subclinical involvement of the respiratory tract. Adult-diagnosed patients have a good response to CF center care, and newly available cystic fibrosis transmembrane receptor-modulating therapies are promising for the treatment of residual function mutation, thus increasing the importance of the diagnosis in adults with unexplained bronchiectasis.

Cystic Fibrosis: A Review of Associated Phenotypes, Use of Molecular Diagnostic Approaches, Genetic Characteristics, Progress, and Dilemmas

Cystic fibrosis (CF) is an autosomal recessive disease with significant associated morbidity and mortality. It is now appreciated that the broad phenotypic CF spectrum is not explained by obvious genotype-phenotype correlations, suggesting that CF transmembrane conductance regulator (CFTR)-related disease may occur because of multiple additive effects. These contributing effects include complex CFTR alleles, modifier genes, mutations in alternative genes that produce CF-like phenotypes, epigenetic factors, and environmental influences. Most patients in the United States are now diagnosed through newborn screening and use of molecular testing methods. We review the molecular testing approaches and laboratory guidelines for carrier screening, prenatal testing, newborn screening, and clinical diagnostic testing, as well as recent developments in CF treatment, and reasons for the lack of a molecular diagnosis in some patients.

Prevalence of meconium ileus marks the severity of mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene

RATIONALE

Meconium ileus (MI) is a perinatal complication in cystic fibrosis (CF), which is only minimally influenced by environmental factors. We derived and examined MI prevalence (MIP) scores to assess CFTR phenotype-phenotype correlation for severe mutations.

METHOD

MIP scores were established using a Canadian CF population (n = 2,492) as estimates of the proportion of patients with MI among all patients carrying the same CFTR mutation, focusing on patients with p.F508del as the second allele. Comparisons were made to the registries from the US CF Foundation (n = 43,432), Italy (Veneto/Trentino/Alto Adige regions) (n = 1,788), and Germany (n = 3,596).

RESULTS

The prevalence of MI varied among the different registries (13-21%). MI was predominantly prevalent in patients with pancreatic insufficiency carrying "severe" CFTR mutations. In this severe spectrum MIP scores further distinguished between mutation types, for example, G542X (0.31) with a high, F508del (0.22) with a moderate, and G551D (0.08) with a low MIP score. Higher MIP scores were associated with more severe clinical phenotypes, such as a lower forced expiratory volume in 1 second (P = 0.01) and body mass index z score (P = 0.04).

CONCLUSIONS

MIP scores can be used to rank CFTR mutations according to their clinical severity and provide a means to expand delineation of CF phenotypes.Genet Med 18 4, 333-340.

Diabetes-related mortality in adults with cystic fibrosis. Role of genotype and sex

RATIONALE

Diabetes is associated with increased mortality in cystic fibrosis. Aggressive screening and early institution of insulin treatment significantly reduced this risk over the period of 1992-2008.

OBJECTIVES

To determine if progressive improvement in cystic fibrosis-related diabetes (CFRD) mortality has continued since 2008, and examine associations with CFTR genotypes linked to pancreatic insufficiency and to sex.

METHODS

Chart review was performed on 664 patients followed from 2008 to 2012.

MEASUREMENTS AND MAIN RESULTS

Overall mortality for patients with CFRD was 1.8 per 100 person-years, compared with 0.5 in patients with CF without diabetes (P = 0.0002); neither rate changed significantly from mortality reported for 2003-2008. Genotype impacted both mortality and diabetes risk: adults with severe CFTR genotypes experienced greater mortality at every age older than 32 years than those with mild genotypes (P = 0.002), and the risk of developing CFRD was also greatly increased in those with severe genotypes (prevalence 60% in adult patients with severe vs. 14% in adults with mild mutations). CFRD had a direct influence on mortality because it was associated with increased risk of death within each genotype category (20 vs. 2%, P = 0.007 for mild; 12 vs. 4%, P = 0.012 for severe). There was also a sex difference in adults with severe CFTR genotypes; both mortality and CFRD prevalence were higher at every age in females than males.

CONCLUSIONS

Despite substantial improvement over time, mortality for CFRD patients greater than 30 years remains higher than for patients with CF without diabetes.

Nutritional advances in patients with respiratory diseases

Nutritional issues are increasingly recognised in the course of respiratory diseases, from primary prevention to advanced disease care. During the 2014 ERS International Congress in Munich, Germany, the topic was addressed in a Clinical Year in Review session. This review highlights new insights in generic and disease-specific nutritional issues from recently published peer-reviewed articles. The clinical relevance of obesity was highlighted in primary and secondary prevention across all respiratory diseases. Radiographic imaging was explored for characterisation of metabolic phenotypes as an integrated part of diagnostic work-up. Muscle regenerative defects and the autophagy-lysosome pathway were identified as new leads for combatting muscle wasting.

Cystic fibrosis genetics: from molecular understanding to clinical application

The availability of the human genome sequence and tools for interrogating individual genomes provide an unprecedented opportunity to apply genetics to medicine. Mendelian conditions, which are caused by dysfunction of a single gene, offer powerful examples that illustrate how genetics can provide insights into disease. Cystic fibrosis, one of the more common lethal autosomal recessive Mendelian disorders, is presented here as an example. Recent progress in elucidating disease mechanism and causes of phenotypic variation, as well as in the development of treatments, demonstrates that genetics continues to play an important part in cystic fibrosis research 25 years after the discovery of the disease-causing gene.

Protein is an important but undervalued macronutrient in the nutritional care of patients with cystic fibrosis

PURPOSE OF REVIEW

Achieving an optimal nutritional status in patients with cystic fibrosis (CF) is important to maintain better pulmonary function, physical performance, and to prolong survival. So far, nutrition care in CF has mainly focused on fat intake and achieving energy balance, but there is increasing information on the clinical importance of muscle maintenance and protein intake in CF.

RECENT FINDINGS

Low muscle mass is consistently associated with pulmonary decline, bone mineral loss, and poor survival in CF. High energy and fat intake contributes to an increased prevalence of overweight and obesity in CF. Obesity per se is not related to better lung function in CF and has negative metabolic and clinical consequences, particularly when muscle wasting is present. Protein digestion capacity is severely impaired in CF, but high protein intake is needed and essential amino acid mixtures appear highly anabolic even in those with severe muscle loss.

SUMMARY

Body composition assessment and achieving protein balance in the routine care in CF is important to prevent muscle loss and further improve the clinical and overall outcome of these patients. New approaches are needed to optimize the interaction between high essential amino-acid-rich protein intake and pancreatic enzyme regimen in CF. The optimal level of protein intake needs to be assessed in clinically stable CF patients as well as in those recovering from an acute exacerbation.

Disease-modifying genes and monogenic disorders: experience in cystic fibrosis

The mechanisms responsible for the determination of phenotypes are still not well understood; however, it has become apparent that modifier genes must play a considerable role in the phenotypic heterogeneity of Mendelian disorders. Significant advances in genetic technologies and molecular medicine allow huge amounts of information to be generated from individual samples within a reasonable time frame. This review focuses on the role of modifier genes using the example of cystic fibrosis, the most common lethal autosomal recessive disorder in the white population, and discusses the advantages and limitations of candidate gene approaches versus genome-wide association studies. Moreover, the implications of modifier gene research for other monogenic disorders, as well as its significance for diagnostic, prognostic, and therapeutic approaches are summarized. Increasing insight into modifying mechanisms opens up new perspectives, dispelling the idea of genetic disorders being caused by one single gene.

Residual α-L-iduronidase activity in fibroblasts of mild to severe Mucopolysaccharidosis type I patients

Three major clinical subgroups are usually distinguished in Mucopolysaccharidosis type I: Hurler (MPS IH, severe presentation), Hurler-Scheie (MPS IH/S, intermediate) and Scheie (MPS IS, mild). To facilitate treatment with hematopoietic stem-cell transplantation, early diagnosis is important for MPS IH patients. Although screening for MPS I in newborns would allow detection at an early age, it may be difficult to predict the phenotype on the basis of the genotype in these infants. Extra diagnostic tools are thus required. Based on the hypothesis that distinct MPS I phenotypes may result from differences in residual α-l-iduronidase (IDUA) activity, we modified the common IDUA assay using the substrate 4-methylumbelliferyl-α-l-iduronide to allow quantification of low IDUA activity in MPS I fibroblasts. Enzyme incubation was performed with high protein concentrations at different time points up to 8h. Mean residual IDUA activity was 0.18% (range 0-0.6) of the control value in MPS IH fibroblasts (n=5); against 0.27% (range 0.2-0.3) in MPS IH/S cells (n=3); and 0.79% (range 0.3-1.8) in MPS IS fibroblasts (n=5). These results suggest that residual IDUA activity and severity of the MPS I phenotype are correlated. Two MPS IS patients with rare (E276K/E276K) or indefinite (A327P/unknown) IDUA genotypes had residual IDUA activity in the MPS IS range, illustrating the usefulness of our approach. IDUA(E276K) was very unstable at 37°C, but more stable at 23°C, suggesting thermal instability. We conclude that this procedure for determining residual IDUA activity in fibroblasts of MPS I patients may be helpful to predict MPS I phenotype.

Pubertal height velocity and associations with prepubertal and adult heights in cystic fibrosis

OBJECTIVES

To test the hypothesis that pubertal peak height velocity (PHV) in cystic fibrosis (CF) has improved and is influenced by prepubertal growth and genetic potential.

STUDY DESIGN

PHV from 1862 children born in 1984-87 and documented in the 1986-2008 US CF Foundation Registry was determined by statistical modeling and classified into normal, delayed (2-SD > average age), attenuated (magnitude <5th percentile), or both delayed and attenuated (D&A). Genetic potential for height was estimated by parental stature.

RESULTS

PHV averaged 8.4 cm/year at age 14.0 years in boys and 7.0 cm/year at age 12.1 years in girls, ∼6-month delay and ∼15% reduction compared with healthy children. PHV was normal in 60%, delayed in 9%, attenuated in 21%, and D&A in 5%. Patients with delayed PHV reached similar adult height percentile (boys: 34th, girls: 46th) to those with normal PHV (boys: 33rd, girls: 34th); both were significantly taller than the attenuated (boys: 11th, girls: 19th) and D&A PHV subgroups (boys: 8th, girls: 14th). Pancreatic-sufficient patients had taller prepubertal and adult heights but similar PHV compared with pancreatic-insufficient or meconium ileus patients. Adjusting for genetic potential reduced adult height percentiles more in boys (from 25th to 16th) than girls (from 28th to 24th). Height at age 7 years, PHV age and magnitude, and parental stature significantly predicted adult height.

CONCLUSIONS

Pubertal PHV has improved in children with CF born after mid-1980s compared with older cohorts but remains below normal. Suboptimal prepubertal and pubertal growth led to adult height below genetic potential in CF.