Heritability of fetal hemoglobin, white cell count, and other clinical traits from a sickle cell disease family cohort.

Sickle cell disease (SCD) is the most common monogenic disorder in the world. Notably, there is extensive clinical heterogeneity in SCD that cannot be fully accounted for by known factors, and in particular, the extent to which the phenotypic diversity of SCD can be explained by genetic variation has not been reliably quantified. Here, in a family-based cohort of 449 patients with SCD and 755 relatives, we first show that 5 known modifiers affect 11 adverse outcomes in SCD to varying degrees. We then utilize a restricted maximum likelihood procedure to estimate the heritability of 20 hematologic traits, including fetal hemoglobin (HbF) and white blood cell count (WBC), in the clinically relevant context of inheritance from healthy carriers to SCD patients. We report novel estimations of heritability for HbF at 31.6% (±5.4%) and WBC at 41.2% (±6.8%) in our cohort. Finally, we demonstrate shared genetic bases between HbF, WBC, and other hematologic traits, but surprisingly little overlap between HbF and WBC themselves. In total, our analyses show that HbF and WBC have significant heritable components among individuals with SCD and their relatives, demonstrating the value of using family-based studies to better understand modifiers of SCD.

Age- and gender-dependent obesity in individuals with 16p11.2 deletion.

Recurrent genomic imbalances at 16p11.2 are genetic risk factors of variable penetrance for developmental delay and autism. Recently, 16p11.2 (chr16:29.5 Mb-30.1 Mb) deletion has also been detected in individuals with early-onset severe obesity. The penetrance of 16p11.2 deletion as a genetic risk factor for obesity is unknown. We evaluated the growth and body mass characteristics of 28 individuals with 16p11.2 (chr16:29.5 Mb-30.1 Mb) deletion originally ascertained for their developmental disorders by reviewing their medical records. We found that nine individuals could be classified as obese and six as overweight. These individuals generally had early feeding and growth difficulties, and started to gain excessive weight around 5-6 years of age. Thirteen out of the 18 deletion carriers aged 5 years and older (72%) were overweight or obese, whereas only two of 10 deletion carriers (20%) younger than five were overweight or obese. Males exhibited more severe obesity than females. Thus, the obesity phenotype of 16p11.2 deletion carriers is of juvenile onset, exhibited an age- and gender-dependent penetrance. 16p11.2 deletion appears to predispose individuals to juvenile onset obesity and in this case are similar to the well-described Prader-Willi syndrome (PWS). Early detection of this deletion will provide opportunity to prevent obesity.

Mirror extreme BMI phenotypes associated with gene dosage at the chromosome 16p11.2 locus.

Both obesity and being underweight have been associated with increased mortality. Underweight, defined as a body mass index (BMI) ≤ 18.5 kg per m(2) in adults and ≤ -2 standard deviations from the mean in children, is the main sign of a series of heterogeneous clinical conditions including failure to thrive, feeding and eating disorder and/or anorexia nervosa. In contrast to obesity, few genetic variants underlying these clinical conditions have been reported. We previously showed that hemizygosity of a ∼600-kilobase (kb) region on the short arm of chromosome 16 causes a highly penetrant form of obesity that is often associated with hyperphagia and intellectual disabilities. Here we show that the corresponding reciprocal duplication is associated with being underweight. We identified 138 duplication carriers (including 132 novel cases and 108 unrelated carriers) from individuals clinically referred for developmental or intellectual disabilities (DD/ID) or psychiatric disorders, or recruited from population-based cohorts. These carriers show significantly reduced postnatal weight and BMI. Half of the boys younger than five years are underweight with a probable diagnosis of failure to thrive, whereas adult duplication carriers have an 8.3-fold increased risk of being clinically underweight. We observe a trend towards increased severity in males, as well as a depletion of male carriers among non-medically ascertained cases. These features are associated with an unusually high frequency of selective and restrictive eating behaviours and a significant reduction in head circumference. Each of the observed phenotypes is the converse of one reported in carriers of deletions at this locus. The phenotypes correlate with changes in transcript levels for genes mapping within the duplication but not in flanking regions. The reciprocal impact of these 16p11.2 copy-number variants indicates that severe obesity and being underweight could have mirror aetiologies, possibly through contrasting effects on energy balance.

Abnormal modulation of cell protective systems in response to ischemic/reperfusion injury is important in the development of mouse sickle cell hepatopathy.

BACKGROUND: Sickle cell disease, a genetic red cell disorder inherited in an autosomal recessive manner, occurs throughout the world. Hepatic dysfunction and liver damage may be present in sickle cell disease, but the pathogenesis of these conditions is only partially understood. DESIGN AND METHODS: Transgenic mice with sickle cell disease (SAD mice) and wild-type mice were exposed to an ischemic/reperfusion stress. The following parameters were evaluated: hematologic profile, transaminase and bilirubin levels, liver histopathology, and mRNA levels of nuclear factor-κB p65, endothelial nitric oxide synthase, inducible nitric oxide synthase, heme oxygenase-1 and phosphodiesterase-1, -2, -3, and -4 genes in hepatocytes obtained by laser-capture microdissection. Immunoblotting was used to analyze the expression of the following proteins: nuclear factor-κB p65 and phospho-nuclear factor-κB p65, heme oxygenase-1, biliverdin reductase, heat shock protein-70, heat shock protein-27 and peroxiredoxin-6. A subgroup of SAD mice was treated with the phosphodiesterase-4 inhibitor rolipram (30 mg/Kg/day by gavage) during the ischemic/reperfusion protocol. RESULTS: In SAD mice the ischemic/reperfusion stress induced liver damage compatible with sickle cell disease hepatopathy, which was associated with: (i) lack of hypoxia-induced nuclear factor-κB p65 activation; (ii) imbalance in the endothelial/inducible nitric oxide synthase response to ischemic/reperfusion stress; (iii) lack of hypoxia-induced increased expression of heme oxygenase-1/biliverdin reductase paralleled by a compensatory increased expression of heat shock proteins 70 and 27 and peroxiredoxin-6; and (iv) up-regulation of the phosphodiesterase-1, -2, -3, and -4 genes. In SAD mice the phosphodiesterase-4 inhibitor rolipram attenuated the ischemic/reperfusion-related microcirculatory dysfunction, reduced the inflammatory cell infiltration and induced the heme oxygenase-1/biliverdin reductase cytoprotective systems. CONCLUSIONS: In SAD mice, sickle cell hepatopathy is associated with perturbed nuclear factor-κB p65 signaling with an imbalance of endothelial/inducible nitric oxide synthase levels, lack of heme oxygenase-1/biliverdin reductase expression and up-regulation of two novel cytoprotective systems: heat shock protein-27 and peroxiredoxin-6.

Pulmonary hypertension and nitric oxide depletion in sickle cell disease.

During the past decade a large body of experimental and clinical studies has focused on the hypothesis that nitric oxide (NO) depletion by plasma hemoglobin in the microcirculation plays a central role in the pathogenesis of many manifestations of sickle cell disease (SCD), particularly pulmonary hypertension. We have carefully examined those studies and believe that the conclusions drawn from them are not adequately supported by the data. We agree that NO depletion may well play a role in the pathophysiology of other hemolytic states such as paroxysmal nocturnal hemoglobinuria, in which plasma hemoglobin concentrations are often at least an order of magnitude greater than in SCD. Accordingly, we conclude that clinical trials in SCD designed to increase the bioavailability of NO or association studies in which SCD clinical manifestations are related to plasma hemoglobin via its surrogates should be viewed with caution.

Distinct and novel SLC26A4/Pendrin mutations in Chinese and U.S. patients with nonsyndromic hearing loss.

Mutations of the human SLC26A4/PDS gene constitute the most common cause of syndromic and nonsyndromic hearing loss. Definition of the SLC26A4 mutation spectrum among different populations with sensorineural hearing loss is important for development of optimal genetic screening services for congenital hearing impairment. We screened for SLC26A4 mutations among Chinese and U.S. subjects with hearing loss, using denaturing HPLC (DHPLC) and direct DNA sequencing. Fifty-two of 55 Chinese subjects with deafness accompanied by enlargement of the vestibular aqueduct (EVA) exhibited at least one mutant SLC26A4 allele, whereas SLC26A4 mutations were found in only 2 of 116 deaf Chinese patients without EVA. The spectrum of SLC26A4 mutations differed among Chinese and U.S. subjects and included 10 previously unreported SLC26A4 variants: 4 in the Chinese population (p.E303Q, p.X329, p.X467, p.X573) and 6 in the U.S. population (p.V250A, p.D266N, p.F354S, p.D697A, p.K715N, p.E737D). Among the seven novel in-frame missense mutations, five encoded SLC26A4 proteins with substantially reduced Cl(-)/anion exchange activity as expressed and measured in Xenopus oocytes, but four of these were sufficiently active to allow study of anion selectivity. The only mutant polypeptide exhibiting complete loss of anion exchange function, p.E303Q, was expressed at or near the oocyte surface at near-wild-type levels. Two variants, p.F354S and p.E737D, displayed selective reduction in relative rate of Cl(-)/HCO(3)(-) exchange compared with similarly measured rates of Cl(-)/Cl(-) and Cl(-)/I(-) exchange. Our data show that mutation analysis of the SLC26A4 gene is of high diagnostic yield among subjects with deafness and bilateral EVA in both China and the U.S. However, the pathogenicity of monoallelic SLC26A4 gene variants in patients with hearing loss remains unclear in many instances.

SLC26A4 c.919-2A>G varies among Chinese ethnic groups as a cause of hearing loss.

PURPOSE: Mutations in the SLC26A4 gene are second only to GJB2 mutations as a currently identifiable genetic cause of sensorineural hearing loss. In most areas of China, genetic testing for sensorineural hearing loss is unavailable because of limited knowledge of the mutation spectrum. Although SLC26A4 c.919-2A>G (IVS7-2A>G) is a common mutation among some Asian populations, the mutation prevalence among various ethnic groups within China has not been studied. METHODS: DNA specimens from 3271 subjects with moderate to profound sensorineural hearing loss from 27 regions of China were genotyped for the c.919-2A>G mutation by polymerase chain reaction/restriction-fragment-length polymorphism. Normal hearing controls from Han (n = 185) and Uigur (n = 152) populations were also tested. RESULTS: Overall, 408 subjects with sensorineural hearing loss (12.5%) carried at least one c.919-2A>G allele, with 158 (4.8%) homozygotes and 250 (7.6%) heterozygotes. Within the subpopulations examined, the rate varies from 0% to 12.2% for c.919-2A>G homozygotes and from 0% to 17.6% for heterozygotes. Based on this cohort, Chinese subjects with sensorineural hearing loss seem to have a relatively higher c.919-2A>G frequency than that of other Asian populations. CONCLUSION: These results demonstrate that a simple and efficient genetic test for the c.919-2A>G mutation alone would identify the molecular cause in up to 8-12% of individuals with sensorineural hearing loss in a few eastern and central regions of China. Those who are negative for the c.919-2A>G mutation would be candidates for further mutational analysis of SLC26A4 or other deafness-related genes. This would greatly improve genetic diagnosis and counseling for a huge number of Chinese individuals and family members with sensorineural hearing loss in China, and many more ethnic Chinese in other countries, which might be up to one million.

Protective effects of phosphodiesterase-4 (PDE-4) inhibition in the early phase of pulmonary arterial hypertension in transgenic sickle cell mice.

Pulmonary arterial hypertension (PAH) is one of the leading causes of morbidity and mortality in adult patients with sickle cell disease (SCD). Here, we developed a model to study the early stage of PAH in SCD. We exposed wild-type and transgenic sickle cell SAD (Hbb(s)/Hbb(s)) mice to hypoxia (8% O(2)) for 7 days. Prolonged hypoxia in SAD mice only induced 1) increased neutrophil count in both bronchoalveolar lavage (BAL) and peripheral circulation; 2) increased BAL IL1beta, IL10, IL6, and TNF-alpha; and 3) up-regulation of the genes endothelin-1, cyclo-oxygenase-2, angiotensin-converting-enzyme, and IL-1beta, suggesting that amplified inflammatory response and activation of the endothelin-1 system may contribute to the early phase of PAH in SCD. Since phosphodiesterases (PDEs) are involved in pulmonary vascular tone regulation, we evaluated gene expression of phosphodiesterase-4 (PDE-4) isoforms and of PDE-1, -2, -3, -7, -8, which are the main cyclic-adenosine-monophosphate hydrolyzing enzymes. In SAD mouse lungs, prolonged hypoxia significantly increased PDE-4 and -1 gene expressions. The PDE-4 inhibitor, rolipram, prevented the hypoxia-induced PDE-4 and -1 gene up-regulation and interfered with the development of PAH, most likely through modulation of both vascular tone and inflammatory factors. This finding supports a possible therapeutic use of PDEs inhibitors in the earlier phases of PAH in SCD.

Association between microdeletion and microduplication at 16p11.2 and autism.

BACKGROUND: Autism spectrum disorder is a heritable developmental disorder in which chromosomal abnormalities are thought to play a role. METHODS: As a first component of a genomewide association study of families from the Autism Genetic Resource Exchange (AGRE), we used two novel algorithms to search for recurrent copy-number variations in genotype data from 751 multiplex families with autism. Specific recurrent de novo events were further evaluated in clinical-testing data from Children's Hospital Boston and in a large population study in Iceland. RESULTS: Among the AGRE families, we observed five instances of a de novo deletion of 593 kb on chromosome 16p11.2. Using comparative genomic hybridization, we observed the identical deletion in 5 of 512 children referred to Children's Hospital Boston for developmental delay, mental retardation, or suspected autism spectrum disorder, as well as in 3 of 299 persons with autism in an Icelandic population; the deletion was also carried by 2 of 18,834 unscreened Icelandic control subjects. The reciprocal duplication of this region occurred in 7 affected persons in AGRE families and 4 of the 512 children from Children's Hospital Boston. The duplication also appeared to be a high-penetrance risk factor. CONCLUSIONS: We have identified a novel, recurrent microdeletion and a reciprocal microduplication that carry substantial susceptibility to autism and appear to account for approximately 1% of cases. We did not identify other regions with similar aggregations of large de novo mutations.

Quantitative trait loci for peripheral blood cell counts: a study in baboons.

Increasingly, baseline peripheral blood cell counts are implicated as risk factors for common complex diseases. While genetic influences on these hematologic parameters are firmly established, the genetic architecture of the blood counts is still poorly understood. In this article we used data from 582 healthy pedigreed baboons and variance components methods to localize quantitative trait loci (QTLs) influencing complete blood count variables. Besides performing genome-wide linkage scans for each trait individually, we conducted bivariate linkage analyses for all pairwise trait combinations to also identify pleiotropic QTLs influencing several blood counts. While significant and suggestive QTLs were localized throughout the genome (LOD range: 1.5-3.5), chromosomal regions associated with the expression of various hematologic parameters stand out. In particular, our results provide significant and consistent evidence for a QTL on the orthologous human chromosome 1p that is shared by several blood counts, mainly erythrocyte parameters. In addition, multiple suggestive evidence of linkage was detected on the orthologous human chromosomes 10 (near the q-terminus) and 19 (centromeric section). Future studies should help identify the genes responsible for these QTL and elucidate their role on baseline variation in hematologic indicators of health and disease.

Prevention and management of stroke in sickle cell anemia.

As the overall health of patients with sickle cell anemia (SS) improves and diagnostic techniques become more sensitive, physicians are seeing patients with an increasingly wide range of subtle and not-so-subtle brain injury. The major breakthrough in the field of sickle-related brain injury has been the unprecedented success of transcranial Doppler ultrasonography (TCD) to identify asymptomatic patients at high risk of stroke, coupled with chronic transfusion therapy to prevent it. The evidence for TCD screening and preventive treatment is strong and compelling, but there are still important unanswered questions regarding the implications of "silent infarcts" found in the magnetic resonance images (MRIs) of asymptomatic individuals, and the growing awareness of the burden of neuropsychiatric dysfunction in otherwise apparently healthy individuals.

Quantitative trait loci for baseline erythroid traits.

A substantial genetic contribution underlies variation in baseline peripheral blood counts. We performed quantitative trait locus/loci (QTL) analyses to identify chromosome (Chr) regions harboring genes influencing the baseline erythroid parameters in F2 intercrosses between NZW/LacJ, SM/J, and C57BLKS/J inbred mice. We identified multiple significant QTL for red blood cell (RBC) count, hemoglobin (Hgb) and hematocrit (Hct) levels, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean cell hemoglobin concentration (CHCM). We identified four RBC count QTL: Rbcq1 (Chr 1, peak LOD score at 62 cM,), Rbcq2 (Chr 4, 60 cM), Rbcq3 (Chr 11, 34 cM), and Rbcq4 (Chr 10, 60 cM). Three MCV QTL were identified: Mcvq1 (Chr 7, 30 cM), Mvcq2 (Chr 11, 6 cM), and Mcvq3 (Chr 10, 60 cM). Single significant loci for Hgb (Hgbq1, Chr 16, 32 cM), Hct (Hctq1, Chr 3, 42 cM), and MCH (Mchq1, Chr 10, 60 cM) were identified. The data support the existence of a common RBC/MCH/MCV locus on Chr 10. Two QTL for CHCM (Chcmq1, Chr 2, 48 cM; Chcmq2, Chr 9, 44 cM) and an interaction between Chcmq2 with a locus on Chr 19 were identified. These analyses emphasize the genetic complexity underlying the regulation of erythroid peripheral blood traits in normal populations and suggest that genes not previously recognized as significantly impacting normal erythropoiesis exist.

Quantitative trait loci for baseline white blood cell count, platelet count, and mean platelet volume.

A substantial genetic contribution to baseline peripheral blood counts has been established. We performed quantitative trait locus/loci (QTL) analyses to identify chromosome (Chr) regions harboring genes influencing the baseline white blood cell (WBC) count, platelet (Plt) count, and mean platelet volume (MPV) in F(2) intercrosses between NZW/LacJ, SM/J, and C57BLKS/J inbred mice. We identified six significant WBC QTL: Wbcq1 (peak LOD score at 38 cM, Chr 1), Wbcq2 (42 cM, Chr 3), Wbcq3 (0 cM, Chr 15), Wbcq4 (58 cM, Chr 1), Wbcq5 (82 cM, Chr 1), and Wbcq6 (8 cM, Chr 14). Three significant Plt QTL were identified: Pltq1 (24 cM, Chr 2), Pltq2 (36 cM, Chr 7), and Pltq3 (10 cM, Chr 12). Two significant MPV QTL were identified, Mpvq1 (62 cM, Chr 15) and Mpvq2 (44 cM, Chr 8). In total, the WBC QTL accounted for up to 31% of the total variance in baseline WBC count, while the Plt and MPV QTL accounted for up to 30% and 49% of the total variance, respectively. These analyses underscore the genetic complexity underlying these traits in normal populations and provide the basis for future studies to identify novel genes involved in the regulation of mammalian hematopoiesis.

Acquisition of mutans streptococci and caries prevalence in pediatric sickle cell anemia patients receiving long-term antibiotic therapy.

PURPOSE: The purpose of this study was to: (1) evaluate the prevalence of mutans streptococci (MS) and dental caries in sickle cell anemia (SCA) patients receiving long-term prophylactic penicillin therapy; and (2) determine changes in MS colonization and dental caries upon discontinuing the antibiotic. METHODS: Sixty subjects with SCA and 60 age- and race-matched control subjects participated in this study. The SCA subjects were divided into 2 separate age groups: (1) group 1 subjects were under 6 years of age and received penicillin twice a day; and (2) group 2 subjects were 6 to 12 years old and received no daily prophylactic antibiotics, although up to age 6 they had received daily penicillin before it was discontinued. DMFS/dmfs scores for all subjects were obtained through a comprehensive dental examination including bitewing radiographs. Stimulated salivary samples to assess MS levels were obtained on all subjects. Data on medical, dental, fluoride, and dietary history were obtained on all patients through a written parental questionnaire. RESULTS: No group 1 patients had positive cultures for MS. In contrast, 70% of marched controls cultured positively for MS (P<.01). The DMFS/dmfs score for group 1 was 0.21 vs 5.1 for the control group (P<.01). Differences in surfaces affected were also noted, with no group 1 patients having interproximal lesions compared to 47% of control subjects having these lesions (P<.01). Group 2 also had significantly lower levels of MS than matched controls (47% vs 97%, P<.01), although there was no statistically significant difference in caries prevalence or surfaces involved. CONCLUSIONS: These findings demonstrate that long-term penicillin prophylaxis in SCA patients likely prevents the acquisition of MS, resulting in significantly lower caries rates in these patients. This benefit occurs only during active administration of the drug, however, and only delays the acquisition of MS.

Genetic influences on peripheral blood cell counts: a study in baboons.

Interperson differences in peripheral blood cell counts in healthy individuals result from genetic and environmental influences. We used multivariate genetic analyses to assess the relative impact of genes and environment on baseline blood cell counts and indices using a pedigreed colony of baboons, an animal with well-documented analogies to human blood physiology. After accounting for age, sex, and weight, we found that genetic influences explain a significant proportion of the remaining variability, ranging from a low of 13.7% for mean corpuscular hemoglobin concentration (MCHC) to a high of 72.4% for red blood cell (RBC) number. Genes influence 38.5% of the variation in baseline white blood cell (WBC) count, a characteristic that correlates with mortality in both the general human population and clinically defined subgroups such as individuals with sickle-cell disease. We examined the interaction between pairs of traits and identified those that share common genetic influences (pleiotropy). We unexpectedly observed that the same gene or group of genes influences both WBC count and mean platelet volume (MPV). We anticipate that this approach will ultimately lead to discovery of novel insights into the biology of related traits, and ultimately identify important genes that affect hematopoiesis.

Reliability of Tanner stage assessments in a multi-center study.

Tanner stage indices have been frequently used in research studies to characterize the level of sexual maturation among adolescents. The Cooperative Study of Sickle Cell Disease (CSSCD) is a large multi-center study in which the assessment of Tanner stage indices has been performed to describe delays in sexual maturation and correlates of delays. Rigorous training, however, in rating Tanner stages was not provided for the clinicians in the study. Data from the CSSCD were analyzed to characterize the reliability of the assessment of sexual maturation in this study, and demonstrate the potential for increasing the reliability by more careful training. In lieu of a gold standard, a maximum likelihood algorithm was employed to examine the longitudinal consistency of Tanner stage assessments. Based on the assumption that the underlying process of sexual maturation is progressive, models were developed that allowed one to estimate jointly the incidence distribution for the attainment of Tanner stages and the error rates of assessment. Estimated false-positive rates for assessing the attainment of Tanner stages from the CSSCD ranged from 2% to 19%. Estimated false-negative rates ranged from 1% to 18%. The occurrence of these errors was found not to vary markedly with the subject's age. Error rates of this magnitude can introduce considerable bias to the estimation of the distribution of Tanner stages and result in serious losses in relative efficiency. While the validity of Tanner stage indices can be demonstrated from study data, the loss in statistical efficiency and power associated with the study error rates was severe. This underscores the utility of careful training in pubertal rating for research studies.