Non-carrier Family Members Research Articles

Developing an international network for Alzheimer’s research: the Dominantly Inherited Alzheimer Network

The Dominantly Inherited Alzheimer Network (DIAN) is a collaborative effort of international Alzheimer disease (AD) centers that are conducting a multifaceted prospective biomarker study in individuals at-risk for autosomal dominant AD (ADAD). DIAN collects comprehensive information and tissue in accordance with standard protocols from asymptomatic and symptomatic ADAD mutation carriers and their non-carrier family members to determine the pathochronology of clinical, cognitive, neuroimaging, and fluid biomarkers of AD. This article describes the structure, implementation, and underlying principles of DIAN, as well as the demographic features of the initial DIAN cohort.

Greater risk of parkinsonism associated with non‐N370S GBA1 mutations

Mutations in β-glucosidase (GBA1) are the most common genetic risk factor for Parkinson disease (PD). There is evidence to suggest that PD risk is greater (1) in GBA1 heterozygotes with non-N370S GBA1 mutations compared to N370S mutations and (2) in GD type 1 (GD1) patients compared to GBA1 heterozygotes. This study aimed to determine the comparative risk of parkinsonism in individuals who are affected or carriers of Gaucher disease (GD) and to ascertain the influence of different GBA1 mutations on risk/clinical expression. We conducted a secondary analysis of cross-sectional data assessing the prevalence of parkinsonism in a population of GD1 patients and their heterozygote and non-carrier family members. Two logistic regression models, both employing a family-specific random effect, were used to assess (1) the association between GBA1 mutation (N370S or non-N370S) and parkinsonism among GBA1 heterozygotes and (2) the association between GBA1 genotype and parkinsonism. Parkinsonism was present in 8.6 % of GD1 (7/81), 8.7 % of GBA1 heterozygotes (18/207), and 2.2 % of non-carriers (1/45). For those greater than 60 years old, parkinsonism was present in 38.5 % (5/13) of GD1 (5/13), 15.3 % of GBA1 heterozygotes (13/85), and 7.1 % of non-carriers (1/14). Among GBA1 heterozygotes, non-N370S mutations were associated with a significantly increased risk of parkinsonism compared to N370S (OR = 22.5; p = 0.035; 95%CI: 1.24, 411). In this population, each additional GBA1 mutation was associated with a non-significant two-fold increased risk of parkinsonism. GBA1 heterozygotes with non-N370S mutations associated with Gaucher disease have an increased risk of parkinsonism compared to those with N370S mutations.

Report of Endometrial Cancer in AustralianBRCA1andBRCA2Mutation-Positive Families

There is evidence that tamoxifen treatment of BRCA1 and BRCA2 carriers for prior breast cancer increases risk of endometrioid subtype endometrial cancer (EC), and suggestive evidence that BRCA1 and BRCA2 mutation carriers may be predisposed to EC in the absence of tamoxifen exposure. We assessed the association of EC with BRCA1 or BRCA2 mutation status in Australasian breast-ovarian families. Report of at least one case of EC was significantly greater in BRCA1-positive families (35/218 (16%); p = .03) and non-significantly greater in BRCA2-positive families (23/189 (12%); p = .6), compared to high-risk breast cancer families without a BRCA1/2 mutation (86/796 (11%)). EC was the first/concurrent cancer for 41% of EC cases with multiple cancer diagnoses from BRCA1/2 families, and early onset for most of these diagnoses. Mutation status was imputed for ungeno-typed individuals from 57 BRCA1/2 pedigrees reporting EC using BRCAPRO. Effects of genotype on EC diagnosis age, and interaction with tamoxifen therapy, were assessed using Cox proportional hazards regression analysis. EC risk was non-significantly marginally greater for BRCA1 carriers (hazard ratio = 1.25, 95%CI = 0.65-2.41), and BRCA2 carriers (HR = 1.12, 95%CI = 0.51-2.45), compared to non-carrier family members. Tamoxifen therapy was highly significantly associated with EC (HR = 6.68, 95%CI = 3.12-15.15; p = 1.7 x 10(-6)) in BRCA1/2 families, with no evidence for interaction between tamoxifen therapy and BRCA1/2 genotype. Our family-based study supports a 7-fold increase in EC risk with tamoxifen exposure for female family members from BRCA1/2 families. Early onset EC in carriers without tamoxifen use suggests that further study is required to assess association of modest EC risk with BRCA1/2 mutation status alone.

Novel ECG markers for ventricular repolarization: Is the QT interval obsolete?

Novel ECG markers for ventricular repolarization: Is the QT interval obsolete?

T-wave morphology abnormalities in benign, potent, and arrhythmogenic Ikr inhibition

There is a consensus on the limited value of the QTc interval prolongation as a surrogate marker of drug cardiotoxicity and as a risk stratifier in inherited long QT syndrome (LQTS) patients. We investigated the interest of repolarization morphology in the acquired and the inherited LQTS. We analyzed 2 retrospective electrocardiographic (ECG) datasets from healthy on/off moxifloxacin and from genotyped KCNH2 patients. We measured QT, RR, and T-peak to T-end intervals, early repolarization duration (ERD) and late repolarization duration, T-roundness, T-amplitude, left (αL) and right slopes of T-waves. We designed multivariate logistic models to predict the presence of the KCNH2 mutation or moxifloxacin while adjusting for the level of QTc prolongation and the level of heart rate in LQT2 patients. Independent learning and validation sets were used. A list of 4,874 ECGs from 411 healthy individuals, 293 from 143 LQT2 carriers and 150 noncarrier family members were analyzed. In the moxifloxacin model, ERD was associated with the presence of the drug (odds ratio = 1.15 per ms increase, confidence interval 1.04 to 1.26, P = .0001) after adjustment for QTc. The model for the LQT2 revealed that left slope was associated with the presence of the KCNH2 mutation (odds ratio = 0.38 per 1.5 μV/ms decrease, confidence interval 0.23 to 0.64, P = .0002). Only T-roundness complemented QTc in the model investigating cardiac events in LQT2. These observations demonstrate that the phenotypic expression of KCNH2 mutations and the effect of IKr-inhibitory drug on the surface electrocardiogram are specific. Future research should investigate whether this phenomenon is linked to different level/form of loss functions of Ikr channels, and whether they could result in different arrhythmogenic mechanisms.

Haplotypes of the I157T CHEK2 germline mutation in ethnically diverse populations

The CHEK2*I157T missense mutation, reported in ethnically diverse, high-risk families, moderately increases breast and colon cancer risk. The present study assessed whether this mutation represents a founder mutation. Participants identified in high risk clinics or from consecutive cancer patients in Israel, Poland, Latvia, and Finland, were either carriers of the CHEK2*I157T mutation or non-carrier family members. Multi-locus genotyping employed two intragenic markers and five CHEK2 gene flanking markers, spanning about 645 kb. Haplotyping was done when families were available for phasing. Overall, 101 individuals (83 I157T*CHEK2 mutation carriers) were genotyped: 16 Finnish individuals from 11 families (14 mutation carriers, two non-carrier family members), 50 Polish individuals (20 families) (35 carriers, 15 non-carriers), 28 unrelated Latvian mutation carriers, and seven Israeli participants (two families) (six mutation carriers, one non-carrier). Overall 36/83 mutation carriers (43%) were diagnosed with breast cancer, 15/83 (18%)-colon cancer, three-ovarian cancer, one-thyroid cancer, and the rest (n = 28) were asymptomatic. A common core haplotype was detected in all I157T*CHEK2 mutation carriers of Israeli, Polish, and Finnish origin between markers D22S275-D22S689 (approximately 258 kb), with a different allele pattern in Latvians. In conclusion, CHEK2*I157T missense mutation is a founder mutation in ethnically diverse populations, but may also be a mutational hotspot.

Molecular and Clinical Characterization of a Novel SCN5A Mutation Associated With Atrioventricular Block and Dilated Cardiomyopathy

Increased susceptibility to dilated cardiomyopathy has been observed in patients carrying mutations in the SCN5A gene, but the underlying mechanism remains unclear. In this study, we identified and characterized, both in vitro and clinically, an SCN5A mutation associated with familial progressive atrioventricular block of adult onset and dilated cardiomyopathy in a Chinese family. Among 32 family members, 5 were initially diagnosed with atrioventricular block after age 30; 4 were studied, 3 of whom later developed dilated cardiomyopathy. We found a heterozygous single-nucleotide mutation resulting in an amino acid substitution (A1180V) in all studied patients and in 6 other younger unaffected members but not in 200 control chromosomes. When expressed with the beta1 subunit, the mutated channels exhibited a -4.5-mV shift of inactivation with slower recovery leading to a rate-dependent Na(+) current reduction and a moderate increase in late Na(+) current. Clinical study revealed that although QRS duration decreased with increasing heart rate in noncarrier family members, this change was blunted in unaffected carriers whose ECG and heart function were normal. Resting corrected QT interval of unaffected carriers was significantly longer than that of noncarriers, even though it was still within the normal range. A1180V expresses a mild Na(+) channel phenotype in vitro and a corresponding clinical phenotype in unaffected mutation carriers, implying that A1180V caused structural heart disease in affected carriers by disturbing Na(+) influx and, hence, cellular Na(+) homeostasis. The high penetrance of A1180V suggests this phenotype as a high risk factor for dilated cardiomyopathy with preceding atrioventricular block.

Troponin T and β-myosin mutations have distinct cardiac functional effects in hypertrophic cardiomyopathy patients without hypertrophy

The validity of genotype:phenotype correlation studies in human hypertrophic cardiomyopathy (HCM) has recently been questioned, yet animal models and in vitro studies suggest distinct effects for different mutations. The aims of this study were to investigate whether distinct HCM-mutations have different consequences for cardiac structure and function in the absence of the confounding effects of hypertrophy. Individuals aged 20-65 belonging to 21 R92W(TNNT2), R403W(MYH7), or A797T(MYH7) mutation-bearing families were investigated with 2D, M-mode, and Doppler echocardiography. Cardiac structural and functional parameters were compared between prehypertrophic mutation-carriers and their non-carrier family members, with concomitant adjustment for appropriate covariates. Findings were evaluated against existing animal and in vitro functional data. The distinct functional effect of the R92W(TNNT) mutation was a relative increase in systolic functional parameters, that of the A797T(MYH7) mutation was reduced diastolic function, while the R403W(MYH7) mutation reduced both systolic and diastolic function. The observed early effects of the R92W(TNNT2) mutation mechanistically fit with prolonged force-transients precipitated by increased Ca(2+) sensitivity of the thin filament, and that of the MYH7 mutations with local ATP depletion. Evaluation of the impact of the mutations on cardiac structure and function in prehypertrophic mutation-carriers, relative to the baseline norm provided by their non-carrier family members, best recapitulated existing animal and in vitro functional data, while inclusion of mutation-carriers with hypertrophy obscured such findings. The results prompt speculation that timely treatment aimed at ameliorating Ca(2+) sensitivity for R92W(TNNT2)-carriers, and energy depletion for MYH7 mutation-carriers, may offer a plausible approach for preventing progression from a preclinical into a decompensated state.

Cognitive changes in the preclinical phase of familial Alzheimer's disease

Few studies have examined the presence of linguistic deficits in the preclinical phase of Alzheimer's disease (AD). A total of 19 healthy carriers of the E280A presenilin-1 gene mutation in chromosome 14 and 21 noncarrier family members from Antioquia, Colombia, were administered a neurolinguistic evaluation of lexical-semantic processes. Both groups were similar in age, educational level, and gender. Carriers scored significantly lower than noncarriers on naming of famous faces. Cognitive changes in lexical-semantic tasks can be detected before the clinical diagnosis of probable familial AD, and a neurolinguistic evaluation may be a useful tool in the early clinical diagnosis of sporadic AD as well.

Linguistic changes in verbal expression: A preclinical marker of Alzheimer's disease

Despite the many studies examining linguistic deterioration in Alzheimer's disease (AD), very little is known about changes in verbal expression during the preclinical phase of this disease. The objective of this study was to determine whether changes in verbal expression occur in the preclinical phase of AD. The sample consisted of 40 healthy Spanish speakers from Antioquia, Colombia. A total of 19 were carriers of the E280A mutation in the Presenilin 1 gene, and 21 were noncarrier family members. The two groups were similar in age and education. All the participants were shown the Cookie Theft Picture Card from the Boston Diagnostic Aphasia Examination and were asked to describe the scene. Specific grammatical and semantic variables were evaluated. The performance of each group was compared using multivariate analyses of the variance for semantic and grammatical variables, and errors. Carriers of the mutation produced fewer semantic categories than noncarriers. In the preclinical phase of AD, changes in verbal expression are apparent and early detection of these differences may assist the early diagnosis of and intervention in this disease.

Diurnal variation of ventricular repolarization in a large family with LQT3-Brugada syndrome characterized by nocturnal sudden death

In patients with long-QT syndrome type 3 (LQT3), symptoms occur particularly at rest or during sleep. As to the underlying mechanism, excessive prolongation of the QT interval at slow heart rates probably plays a role. The purpose of the present study was to investigate QT interval prolongation unrelated to heart rate comparing nighttime and daytime in a family with features of both LQT3 and Brugada syndrome. The study group consisted of 38 carriers of the mutant gene (SCN5A, 1795insD) and 30 noncarrier family members, who served as controls. Holter monitoring was performed with beat-to-beat QT interval measurement. In addition, in a subset of subjects, an exercise test and a pacing test (carriers only) with measurement of the RT interval were performed. In carriers, the slope between heart rate and QT interval was significantly steeper during nighttime (0:00 a.m. to 6:00 a.m.) than during daytime (8:00 a.m. to 22:00 p.m.) (regression coefficient -6.18 and -2.80, respectively), (p=0.03),no such effect being observed in the noncarriers. Further, the RT interval was markedly shorter during recovery than during exercise in carriers but not in noncarriers. In contrast, during AAI pacing in the carriers, RT interval shortening along with increasing heart rate was followed by a comparable prolongation of the RT interval along with subsequent decreasing heart rate. In this large LQT3-Brugada syndrome family, carriers of the mutant gene (SCN5A, 1795insD) are characterized by diurnal variation of ventricular repolarization by exhibiting QT interval prolongation, which is more pronounced during nighttime compared with daytime, even when taking into account differences in heart rate. The autonomic nervous system appears to play a role in mediating this effect. This observation may be of relevance for explaining the high incidence of nocturnal sudden death in this family, but this remains to be proven. In addition, whether our findings also apply to other families with LQT3 is uncertain.

Heterozygous Mutations in Natriuretic Peptide Receptor-B (NPR2) Are Associated with Short Stature

C-type natriuretic peptide (CNP) is an important regulator of skeletal growth. Loss-of-function mutations affecting the CNP receptor natriuretic peptide receptor-B (gene NPR2) cause the autosomal recessive skeletal dysplasia, acromesomelic dysplasia, Maroteaux type (AMDM). The phenotype of heterozygous carriers of NPR2 mutations is less clear. The objective of the study was to determine the phenotypic features of heterozygous carriers of NPR2 mutations. This was a case-control study from the general community. Thirty-nine members of a family in which one member has AMDM were studied. This was an observational study. The primary measure was stature, with the hypothesis that carriers have reduced stature compared with noncarriers. Sixteen family members were NPR2 mutation carriers. Height z-scores of these carriers were -1.8 +/- 1.1 (mean +/- sd), which was significantly less than the 23 noncarrier family members (-0.4 +/- 0.8, P < 0.0005) and the general population (P < 0.0005). However, there was no difference in body proportion between carriers and noncarriers. The proband with AMDM had low IGF-I levels and evidence of GH resistance, as well as very high plasma levels of CNP and its amino-terminal propeptide. Levels of these peptides were normal in the heterozygous carriers. We have shown that heterozygous mutations in NPR2 are associated with short stature. Assuming one in 700 people unknowingly carry an NPR2 mutation, our data suggest that approximately one in 30 individuals with idiopathic short stature are carriers of NPR2 mutations.

Autosomal recessive hypercholesterolemia (ARH) and homozygous familial hypercholesterolemia (FH): A phenotypic comparison

Autosomal recessive hypercholesterolemia (ARH) is a rare disorder, due to complete loss of function of an adaptor protein (ARH protein) required for receptor-mediated hepatic uptake of LDL. ARH is a phenocopy of homozygous familial hypercholesterolemia (HoFH) due to mutations in LDL receptor (LDLR) gene; however, previous studies suggested that ARH phenotype is less severe than that of HoFH. To test this hypothesis we compared 42 HoFH and 42 ARH patients. LDLR and ARH genes were analysed by Southern blotting and sequencing. LDLR activity was measured in cultured fibroblasts. In ARH plasma LDL cholestrol (LDL-C) level (14.25 ± 2.29 mmol/L) was lower than in receptor-negative HoFH (21.38 ± 3.56 mmol/L) but similar to that found in receptor-defective HoFH (15.52 ± 2.39 mmol/L). The risk of coronary artery disease (CAD) was 9-fold lower in ARH patients. No ARH patients ≤20 years of age were found to have CAD as opposed to 43% of HoFH. The CAD prevalence was or tended to be lower in ARH also in the 21–40 (45% versus 86%) and 41–60 (78% versus 100%) age groups. Heterozygous ARH carriers showed higher level of LDL-C (+17%) than non-carrier family members. In conclusion the clinical phenotype of ARH is milder than that of receptor-negative HoFH and resembles that observed in receptor-defective HoFH.

Combined monogenic hypercholesterolemia and hypoalphalipoproteinemia caused by mutations in LDL-R and LCAT genes

We studied a three generation family with co-dominant monogenic hypercholesterolemia and hypoalphalipoproteinemia. The proband, a 48 year-old male, was found to be heterozygous for a previously reported mutation in LDL receptor ( LDL-R) gene (IVS15–3 c>a) and a novel mutation in exon 6 of lecithin cholesterol acyltransferase ( LCAT) gene (c.803 G>A) causing a non-synonymous amino acid substitution (p.R244H). These mutations segregated independently in the family. The LDL-R mutation was associated with high levels of LDL-C (6.20–9.85 mmol/L) and apo B (170–255 mg/dL), comparable to those previously reported in carriers of the same mutation. The LCAT mutation was associated with low levels of HDL-C (0.67–0.80 mmol/L) and apo A-I (96–110 mg/dL). The proband had reduced LCAT function, as measured by cholesterol esterification rate (29 nmol/(mL/h) versus 30–60 nmol/(mL/h)), LCAT activity (10 nmol/(mL/h) versus 20–55 nmol/(mL/h)) and LCAT mass (2.87 μg/mL versus 3.1–6.7 μg/mL). Carriers of LCAT mutation had lower LCAT activity and a tendency to reduced cholestrol esterification rate (CER) and LCAT mass as compared to non-carrier family members. The LCAT mutation was not found in 80 control subjects and 60 patients with primary hypoalphalipoproteinemia. Despite the unfavourable lipoprotein profile, the proband had only mild clinical signs of atherosclerosis. This unexpected finding is probably due to the intensive lipid lowering treatment the patient has been on over the last decade.

Longitudinal assessment of the nevus phenotype in a melanoma kindred.

Phenotypic characteristics of members of a melanoma prone kindred with a V126D CDKN2A gene mutation were monitored over approximately 15 y. Thirty-eight previously studied subjects were recruited. Participants underwent a complete skin examination by the same dermatologist who examined them initially. The size and location of all nevi were recorded on a body map diagram. Total nevus number (TNN) and total nevus density (TND) were determined. CDKN2A sequencing verified 13 mutation carriers and 16 non-carriers. Nine participants were spouse controls without a history of melanoma and did not carry a CDKN2A mutation. Mutation carriers demonstrated a greater mean TNN and TND at initial and follow-up examinations compared with non-carriers and continued to develop nevi rather than show nevus regression seen in non-carriers and spouse controls. Non-carriers showed an intermediate nevus phenotype between mutation carriers and spouse controls. Four of the 13 mutation carriers and one non-carrier have developed invasive melanoma. Over a 15-y interval, TNN and TND were increased in mutation carriers compared with non-carriers and spouse controls. Continued accumulation of nevi in mutation carriers supports a nevogenic role for this CDKN2A mutation. An intermediate nevus phenotype in non-carrier family members suggests the presence of additional modifier genes.

Recurrent mutations of the apolipoprotein A-I gene in three kindreds with severe HDL deficiency

Two siblings with high density lipoprotein (HDL) deficiency and no plasma apolipoprotein A-I (Apo A-I) were found to be homozygous for a cytosine deletion in exon 3 of Apo A-I gene (c.85 del C, Q5FsX11). This mutation causes a frameshift leading to a premature stop codon and abolishes the synthesis of Apo A-I. Although both siblings had corneal opacifications and planar xanthomas, only one of them had premature coronary artery disease, probably as the result of mildly elevated LDL levels. In two other unrelated subjects HDL deficiency was due to heterozygosity for a nucleotide substitution in exon 4 of Apo A-I gene (c.494 T>G, L141R). Both Apo A-I mutations were reported previously in an Italian kindred which included compound heterozygotes and simple heterozygotes. We investigated all carriers of these mutations in the three kindreds and in the one previously reported. Plasma Apo A-I and HDL-C levels were lower in the mutation carriers than in non-carrier family members. These levels, however, were lower in L141R carriers than in carriers of c.85 del C. Haplotype analysis performed using several polymorphisms suggested that both the c.85 del C and L141R are likely to be recurrent mutations.

Beat-to-Beat repolarization variability in LQTS patients with the SCN5A sodium channel gene mutation.

Current techniques evaluating beat-to-beat variability of repolarization rely on accurate determination of T wave endpoints. This study proposes a T wave endpoint-independent method to quantify repolarization variability in a standard 12-lead ECG using a wavelet transformation. Our method was used to identify repolarization variability in long QT syndrome patients (LQTS) with the SCN5A sodium channel gene mutation. Using wavelet transformations based on the second Gaussian derivative, we evaluated repolarization variability in 11 LQTS patients with the mutation, 13 noncarrier family members, and 28 unrelated healthy subjects. Time-domain repolarization variability parameters (SDRTo, SDRTm) and wavelet parameters describing temporal (beat-to-beat) variability of repolarization in time (TVT) and in amplitude (TVA) were analyzed. Reproducibility of wavelet parameters and relationship of wavelet-based variability with heart rate and preceding RR interval were investigated. The wavelet-based method quantified beat-to-beat variability of the entire repolarization segment (regardless of QT interval identification) providing insight into variability in repolarization morphology. Our method showed that SCN5A carriers have significantly increased repolarization variability in amplitude (23% +/14% vs 8 +/- 4%, P < 0.001) and in time (14 +/- 17 ms vs 3 +/-2 ms, P < 0.004) compared to noncarriers. Variability of repolarization amplitude was found to be heart rate dependent with variability decreasing with increasing heart rate. Relative error describing reproducibility of TVA and TVT was < or = 5% and < or =10%, respectively. Our method quantifies repolarization variability in amplitude and in time without the need to identify T or U wave endpoints. Wavelet-detected repolarization variability contributes to phenotypic identification of SCN5A carriers, with more pronounced beat-to-beat variability in repolarization amplitude than in time.

A novel mutant, ApoA-I nichinan (Glu235-->0), is associated with low HDL cholesterol levels and decreased cholesterol efflux from cells.

A novel variant of apolipoprotein (apo) A-I associated with low high density lipoprotein (HDL) cholesterolemia has been identified in a Japanese family during screening for apoA-I variants by isoelectric focusing (IEF) gel analysis. ApoA-I (Glu235-->0) Nichinan was caused by a 3-bp deletion of nucleotides 1998 through 2000 in exon 4 of the apoA-I gene. Four subjects in the family were heterozygous carriers for this mutation; the mean plasma concentrations of apoA-I and HDL cholesterol of affected family members were 30% and 32% lower, respectively, than those of unaffected family members. There were no differences in the levels of very low density lipoprotein and low density lipoprotein cholesterol, triglycerides, and other apolipoproteins between the carriers and the noncarrier family members. In the proband, plasma lecithin:cholesterol acyltransferase activity was normal. Functional consequences of the mutation were examined by expressing the mutated and wild-type proapoA-I cDNAs in Escherichia coli. Cholesterol efflux to recombinant proapoA-I Nichinan from mouse peritoneal macrophages loaded with [3H]cholesterol-labeled acetylated low density lipoprotein was decreased by 54% when compared that of normal recombinant proapoA-I. In vivo turnover studies in normal rabbits demonstrated that the recombinant proapoA-I Nichinan was rapidly cleared (22% faster) compared with normal recombinant proapoA-I. We conclude that apoA-I (Glu235-->0) Nichinan induced a critical structural change in the carboxyl-terminal domain of apoA-I for cellular cholesterol efflux and increased the catabolism of apoA-I, resulting in low HDL cholesterol levels.