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Unexpected inheritance of the (CGG)n trinucleotide expansion in a fragile X syndrome family.

The fragile X syndrome is the most frequent cause of inherited mental retardation. CGG repeat alleles are usually classified as normal, premutation, or full mutation based on the length of this triplet in the 5' untranslated region of the FMR1 gene. The pattern of inheritance follows a two-stage intergenerational process in which the premutation evolves into the full mutation. Some reverse mutations have been described, but they appear to be very rare. We describe a family in which a mother of two affected males herself carried a full mutation. Surprisingly, her clinically normal daughter, initially considered to be a carrier by linkage analysis, carried a very short premutation. Findings from our family study corroborate the hypothesis that the expansion during female transmission could be a postzygotic event and raise the problem of mosaicism.

Blotting, Southern↗

Heterogeneous sympathetic innervation in German shepherd dogs with inherited ventricular arrhythmia and sudden cardiac death.

BACKGROUND: Recently, a colony of German shepherd dogs with inherited spontaneous cardiac arrhythmias and associated sudden death has been developed and characterized. Due to the median age of onset of the arrhythmia (4.5 months), the tendency for the arrhythmia to occur during REM sleep or after exercise, and the absence of structural heart disease, we hypothesized a developmental abnormality of the sympathetic innervation to the heart. METHODS AND RESULTS: We studied 11 dogs from this colony, ranging in age from 6 months to 6 years, and four 7-month-old German shepherd dogs unrelated to the colony as controls. We imaged the distribution of functional myocardial sympathetic innervation and perfusion with [123I]metaiodobenzylguanidine (MIBG) and 201Tl, respectively. Sympathetic nerve distribution was evaluated morphologically by immunocytochemical localization of tyrosine hydroxylase. All of the hearts showed evidence of a regional decrease in MIBG uptake, ranging from 5.3% to 53.4% of the myocardium, whereas control dogs showed homogeneous MIBG uptake. Immunocytochemical studies on sections from regions with decreased MIBG uptake showed a striking paucity of nerves compared with regions with normal MIBG uptake, confirming denervation. When the dogs were grouped into those with (n=6) and without (n=5) evidence of ventricular tachycardia on ambulatory ECG, the group with ventricular tachycardia showed 35+/-16.5% denervation, whereas the group without ventricular tachycardia showed 12+/-5.6% denervation (P<.02). CONCLUSIONS: Abnormal heterogeneous sympathetic innervation exists in these dogs with inherited ventricular arrhythmia and sudden cardiac death. Mechanisms relating the presence and extent of regional denervation to the incidence of ventricular arrhythmia remain to be defined.

3-Iodobenzylguanidine↗

Inheritance of salt-dependent hypertension in the inbred Dahl rat.

The mode of inheritance of salt-dependent hypertension in the inbred Dahl salt-sensitive rat strain was examined by genetic crosses with the corresponding salt-resistant strain. The blood pressure responses to ingestion of a high NaCl (8%) diet defined three phenotypes: early onset (within 17 days) of systolic hypertension, defined as greater than or equal to 140 mm Hg, the parental salt-sensitive phenotype; late onset of systolic hypertension requiring 50 to 60 days in males and more than 200 days in females, characteristic of the F1 progeny; and normotension, less than 140 mm Hg, the parental salt-resistant phenotype. The frequencies of the phenotypes observed among 91 F2 progeny and 45 progeny of the backcross to parental salt-sensitive animals agree well with values predicted by a model in which two autosomal, unlinked, allelic loci, termed alpha and beta, determine the inheritance. For F2 male progeny, the predicted frequencies of early-onset hypertension, late-onset hypertension, and normotension are 0.1875, 0.5625, and 0.25, respectively, and the corresponding observed frequencies were 0.156, 0.50, and 0.34 (X2 = 0.48, P > .50). F1 progeny of reciprocal parental crosses were maintained on the 8% NaCl diet for 255 days. Male F1 rats developed systolic hypertension sooner than did females. From 60 to 200 days, the average blood pressure value within each group remained approximately stable; the male values exceeded those for females (P < .01); and the direction of the parental cross significantly influenced (P < .05) the levels in males and females, suggestive of genomic imprinting.

Analysis of Variance↗

Age-related changes in the concentration of plasma cholesterol and triglycerides in two groups of rats with inherited widely different levels of spontaneous physical activity.

The plasma concentration of cholesterol and triglycerides was determined in two groups of rats with inherited widely different levels of spontaneous physical activity. Active as well as passive rats of each sex were divided into two subgroups, one with free access to wheel running activity (exercising group), and another for which admittance to the drum was closed (nonexercising group). Plasma concentrations of cholesterol and triglycerides were followed from the age of 3-8 months in females and 3 months to 1 year in males. A pronounced increase with age in the plasma concentration of these lipids was observed in the active male rats. In the passive male rats and in all females, there were no major changes in plasma levels of cholesterol and triglycerides. Corresponding groups of exercising and nonexercising rats had similar plasma levels of these components. The data for male rats show a positive association between the inherited tendency to perform spontaneously a high level of physical activity and an age-related increase in plasma lipids. However, running activity per se does not seem to have any influence on the level of plasma cholesterol and triglycerides in these rats.

Age Factors↗

On the inheritance of intracranial aneurysms.

BACKGROUND AND PURPOSE: The familial occurrence of intracranial aneurysms suggests the presence of a genetically determined underlying arteriopathy. The pattern of inheritance in these families usually is not known. METHODS: A family with seven members with intracranial aneurysms is described and, from the literature before 1994, a total of 238 families with 560 affected members (56% female and 44% male) with intracranial aneurysms not associated with a known heritable disease are reviewed. A segregation analysis was performed on 73 of these families. RESULTS: Two members were affected in the great majority of families (79%); five or more members were reported in only eight families (3%). The most common affected kinship was among siblings. Angiographic screening in 12 families detected an intracranial aneurysm in 29% of 51 asymptomatic relatives. Segregation analysis revealed several patterns of inheritance that were consistent with the compiled pedigrees, but no single mendelian model was the overall best fitting, suggesting that genetic heterogeneity may be important. Twenty-two percent of siblings of male probands had an intracranial aneurysm compared with 9% of siblings of female probands (P = .003). CONCLUSIONS: Genetic heterogeneity may be important in the genetics of intracranial aneurysms. In families with intracranial aneurysms, siblings of an affected male proband may be at a higher risk of developing an aneurysm than siblings of an affected female proband. Screening for intracranial aneurysms in asymptomatic relatives should be considered in families with two or more affected members. In most families, the nature of the underlying arteriopathy remains obscure.

Adult↗

Inherited thrombophilia in ischemic stroke and its pathogenic subtypes.

BACKGROUND AND PURPOSE: One or more of the inherited thrombophilias may be causal risk factor for a proportion of ischemic strokes, but few studies have addressed this association or the association between thrombophilia and pathogenic subtypes of stroke. METHODS: We conducted a case-control study of 219 hospital cases with a first-ever ischemic stroke and 205 randomly selected community control subjects stratified by age, sex, and postal code. With the use of established criteria, cases of stroke were classified by pathogenic subtype in a blinded fashion. The prevalence of conventional vascular risk factors; fasting plasma levels of protein C, protein S, antithrombin III; and genetic tests for the factor V Leiden and the prothrombin 20210A mutation were determined in cases and control subjects. RESULTS: The prevalence of any thrombophilia was 14.7% (95% CI, 9.9% to 19.5%) among cases and 11.7% (95% CI, 7.4% to 17.0%) among control subjects (OR, 1.3; 95% CI, 0.7% to 2.3%). The prevalence of individual thrombophilias among cases ranged from 0.9% (95% CI, 0.1% to 3.4%) for protein S deficiency to 5.2% (95% CI, 0.3% to 9.1%) for antithrombin III deficiency; among control subjects, the prevalence ranged from 1.0% (95% CI, 0.1% to 3.6%) for protein S deficiency to 4.1% (95% CI, 0.2% to 7.8%) for antithrombin III deficiency. There were no significant differences in the prevalence of thrombophilia between cases and control subjects or between pathogenic subtypes of ischemic stroke. CONCLUSIONS: One in 7 patients with first-ever acute ischemic stroke will test positive for one of the inherited thrombophilias, but the relation is likely to be coincidental rather than causal in almost all cases, irrespective of the pathogenic subtype of the ischemic stroke. These results suggest that routine testing for thrombophilia in most patients with acute ischemic stroke may be unnecessary. Whether the thrombophilias may still be important in younger patients with ischemic stroke or in predicting complications (eg, venous thrombosis) and stroke outcome remains uncertain.

Aged↗

Novel locus for an inherited cardiomyopathy maps to chromosome 7.

BACKGROUND: Genetic mutations are the most common cause of hypertrophic cardiomyopathy (HCM) and an increasingly recognized cause of dilated cardiomyopathy. Autosomal dominant HCM is caused by mutations in sarcomere proteins; such mutations are not universally present, however, and fail to account for &40% of cases of phenotypic HCM. To add further complexity, other genetic origins can mimic the gross clinical phenotype of HCM, and mutations in sarcomere genes have been demonstrated to cause dilated cardiomyopathy. METHODS AND RESULTS: To explore novel genetic causes of inherited cardiomyopathies, genome-wide linkage analysis was used to study one kindred (4 generations, 32 individuals) with predominant clinical features of left ventricular hypertrophy in addition to cardiac dilation, end-stage heart failure, and sudden death. Of note, histopathology from 2 family members did not demonstrate myocyte disarray and fibrosis, indicating that this phenotype is not typical sarcomere mutation HCM. Direct DNA sequencing was performed on sarcomere genes known to cause HCM and dilated cardiomyopathy, and no mutations were identified. Linkage was then established to a novel locus on chromosome 7 (7p12.1-7q21). A maximum 2-point logarithm of odds score of 4.11 was obtained. Recombination events refine the disease interval between D7S506 and D7S3314, corresponding to a distance of 27.2 megabases. CONCLUSIONS: The discovery of a novel genetic locus in this family provides more evidence that molecular pathways leading to inherited cardiac hypertrophy extend beyond the sarcomere. Identification of the causal gene mutation and additional genotype-phenotype correlation studies will provide fundamental insight into mechanisms of cardiac remodeling.

Alleles↗

Inheritance of human alpha-1-acid glycoprotein (orosomucoid) variants.

Although variants of sialic acid-free alpha(1)-acid glycoprotein have been described in human beings, the mode of inheritance of these types has not been reported previously. With the use of a new technique of immunofixation after agarose gel electrophoresis of neuraminidase-treated whole serum, the present study demonstrates that the types of alpha(1)-acid glycoprotein variants in family members are consistent with inheritance as autosomal traits with codominant expression. Gene frequencies have been determined for several ethnic groups. Of a total of 11 maternal-cord serum pairs, seven were discordant types, indicating that the fetus synthesizes alpha(1)-acid glycoprotein and confirming a previous report that there is no significant transplacental passage of this protein.

Animals↗

An inherited enzymatic defect in porphyria cutanea tarda: decreased uroporphyrinogen decarboxylase activity.

Uroporphyrinogen decarboxylase activity was measured in liver and erythrocytes of normal subjects and in patients with porphyria cutanea tarda and their relatives. In patients with porphyria cutanea tarda, hepatic uroporphyrinogen decarboxylase activity was significantly reduced (mean 0.43 U/mg protein; range 0.25-0.99) as compared to normal subjects (mean 1.61 U/mg protein; range 1.27-2.42). Erythrocyte uroporphyrinogen decarboxylase was also decreased in patients with porphyria cutanea tarda. The mean erythrocyte enzymatic activity in male patients was 0.23 U/mg Hb (range 0.16-0.30) and in female patients was 0.17 U/mg Hb (range 0.15-0.18) as compared with mean values in normal subjects of 0.38 U/mg Hb (range 0.33-0.45) in men and 0.26 U/mg Hb (range 0.18-0.36) in women. With the erythrocyte assay, multiple examples of decreased uroporphyrinogen decarboxylase activity were detected in members of three families of patients with porphyria cutanea tarda. In two of these families subclinical porphyria was also recognized. The inheritance pattern was consistant with an autosomal dominant trait. The difference in erythrocyte enzymatic activity between men and women was not explained but could have been due to estrogens. This possibility was supported by the observation that men under therapy with estrogens for carcinoma of the prostate had values in the normal female range. It is proposed that porphyria cutanea tarda results from the combination of an inherited defect in uroporphyrinogen decarboxylase and an acquired factor, usually siderosis associated with alcoholic liver disease.

5-Aminolevulinate Synthetase↗

Dominant inheritance of large molecular weight immunoreactive glucagon.

Plasma from some individuals contains substances which are reactive with glucagon antiserum, are larger than 3,500-dalton glucagon, and have been proposed as possible precursors of glucagon. We have evaluated three generations of a kindred in which 9 of 15 members evaluated had elevated plasma levels of large molecular weight immunoreactive glucagon (L-IRG) with an average concentration of 822 pg/ml. The distribution of individuals with elevated L-IRG levels in this pedigree is consistent with autosomal dominant inheritance. Gel filtration of plasma revealed that all affected family members had excessive amounts of two L-IRG peaks, one with a molecular weight of approximately 9,000 daltons and another in the 10,000 to 20,000-dalton range. Oral glucose tolerance tests were nondiabetic and elicited a fall in L-IRG levels, whereas L-IRG concentrations rose dramatically during the infusion of arginine. These L-IRG species may be precursors of 3,500-DALTON GLUCAGON AND MAY BE ELEVATED in this kindred because of an inherited defect in either their synthesis or degradation.

Adolescent↗

Inherited methylmalonyl CoA mutase apoenzyme deficiency in human fibroblasts: evidence for allelic heterogeneity, genetic compounds, and codominant expression.

We have measured and characterized methylmalonyl coenzyme A (CoA) mutase activity in extracts of cultured human fibroblasts from 23 patients with inherited deficiency of the mutase apoenzyme and from eight obligate heterozygotes for this defect. The mutant cell lines fall into two categories. Those without detectable residual mutase activity in cell extracts (>0.1% of control), and whose ability to utilize propionate in intact cells is refractory to supplementation of the culture medium with hydroxocobalamin, are designated mut degrees mutants. Those with detectable residual activity in cell extracts ( approximately 0.5-50% of control), and whose ability to utilize propionate in intact cells in markedly increased by hydroxocobalamin supplementation, are designated mut(-) mutants. The mutant enzyme in the mut(-) mutants exhibits a 50- to 5,000-fold elevated Michaelis constant (K(m)) for adenosylcobalamin in vitro, a normal K(m) for methylmalonyl CoA, and a strikingly reduced thermal stability at 45 degrees C relative to control. Mutase from one mut(-) mutant turns over at a rate three to four times that of control enzyme when cells are grown in hydroxocobalamin-supplemented medium.To detect heterozygous carriers of mutant mut alleles, we compared mutase activity in fibroblast extracts from four controls with that from eight parents of either mut degrees or mut(-) mutants. After cell growth in either unsupplemented or hydroxocobalamin-supplemented medium, activity in cell lines from heterozygotes was reduced to 47 or 37% of the mean control activities, respectively. We also examined the effect of adenosylcobalamin concentration on reaction kinetics of mutase from heterozygote cell lines. All four cell lines from parents of mut(-) mutants exhibited complex enzyme kinetics; approximately 80% of mutase activity demonstrated a K(m) indistinguishable from control, whereas a smaller component of activity exhibited a K(m) similar to the abnormal K(m) expressed by the mut(-) propositus in each family. In two families with a mut degrees propositus, mutase from three of the four parents exhibited only the normal K(m) for adenosylcobalamin, whereas mutase from one parent displayed complex kinetics, indicating expression of both a normal allele (mut(+)) and a mutant allele with an abnormal K(m). From these studies, we conclude that mut mutants reflect mutations at the autosomal gene locus for the methylmalonyl CoA mutase apoenzyme; that mut degrees , mut(-), and mut(+) alleles at this locus are codominantly expressed; and that some mut mutants may be genetic compounds, inheriting two different mut degrees or mut(-) alleles from their parents.

Alleles↗

X-linked inheritance in females with chronic granulomatous disease.

Chronic granulomatous disease in males is familial and its transmission is is usually clearly x-linked. The mode of inheritance in females with the syndrome is unknown and the carrier state difficult to identify. Defective polymorphonuclear leukocyte bactericidal activity in this disease is associated with an absence of the respiratory burst generated in stimulated phagocytes and may be detected by the chemiluminescence assay. Polymorphonuclear leukocytes from three of four females with chronic granulomatous disease had extremely low chemiluminescence production, their asymptomatic mothers had intermediate values, and their fathers were normal. Polymorphonuclear neutrophils of two affected males in these kinships generated no chemiluminescence, whereas two of seven female relatives had intermediate values, and all nonaffected males had normal values. In the three families in which leukocytes were studied by nitroblue tetrazolium reduction, two populations of neutrophils were demonstrated for the female patients and/or their mothers. The wide phenotypic variability for clinical disease, evidence of two leukocyte populations in the patients or their mothers, and low but detectable leukocyte chemiluminescence in the affected females is consistent with the Lyon hypothesis of x-chromosome inactivation in these families. The findings suggest an x-linked inheritance in these females with chronic granulomatous disease.

Female↗

Molecular analysis of the beta-thalassemia phenotype associated with inheritance of hemoglobin E (alpha 2 beta2(26)Glu leads to Lys).

Inheritance of the gene for betaE-globin is associated with hypochromia and microcytosis, reminiscent of typical heterozygous beta-thalassemia. Patients with hemoglobin (Hb)E-beta-thalassemia exhibit clinical phenotypes of severe beta-thalassemia, a circumstance not encountered in other compound heterozygous states for structural beta-chain mutations and beta-thalassemia. We have analyzed the kinetics of globin synthesis and the levels of globin messenger (m) RNA accumulation in patients with Hb E-beta-thalassemia and Hb E trait. The initial rate of beta-globin synthesis (betaE/alpha=0.20-0.34) was less than expected on the basis of gene dosage, or comparable studies of other compound heterozygous states for beta-thalassemia and structurally abnormal beta-chains. betaE-globin synthesis was not only reduced during short-term incubations (1-5 min), but also remained relatively unchanged during long-term pulse or chase incubations up to 5h. Analysis of globin mRNA by cell-free translation and molecular hybridization confirmed that the unexpectedly low levels of betaE-globin synthesis were associated with comparable reduction in the levels of beta-globin mRNA. In Hb E-beta-thalassemia the betaA + betaE (alpha globin nRNA ratio observed were substantially lower than those obtained from reticulocytes of patients with heterozygous beta-thalassemia, or Hb S-betaO-thalassemia, while in Hb E trait, the betaA + betaE/alpha mRNA ratio was in the ranged observed for beta-thalassemia trait. The betaE-globin gene specifies reduced accumulation of betaE-globin mRNA, a property characteristic of other forms of beta-thalassemia. The beta-thalassemia phenotype associated with inheritance of Hb E is thus determined at the level of beta-globin mRNA metabolism.

Globins↗

Inherited incomplete deficiency of the fourth component of complement (C4) determined by a gene not linked to human histocompatibility leukocyte antigens.

We have studied a family in which the proband had systemic lupus erythematosus and selective incomplete deficiency of the fourth component of complement (C4) (2-5% of the normal level). An additional six healthy family members also had low C4 levels (2.4-24.1% of normal) but no evidence of lupus. This form of inherited C4 deficiency differs from that in previously reported families in that inheritance was autosomal dominant (rather than recessive), C4 levels were markedly reduced (but not undetectable), and there was no linkage to HLA, BF, or C4 structural loci, all known to be within the major histocompatibility complex.

Adult↗

Alternative splicing: a mechanism for phenotypic rescue of a common inherited defect.

Approximately 2% of Caucasians and African-Americans are homozygous for a nonsense mutation in exon 2 of the AMPD1 (AMP deaminase) gene. These individuals have a high grade deficiency of AMPD activity in their skeletal muscle. More than 100 patients with AMPD1 deficiency have been reported to have symptoms of a metabolic myopathy, but it is apparent many individuals with this inherited defect are asymptomatic given the prevalence of this mutant. Results of the present study provide a potential molecular explanation for "correction" of this genetic defect. Alternative splicing eliminates exon 2 in 0.6-2% of AMPD1 mRNA transcripts in adult skeletal muscle. Expression studies document that AMPD1 mRNA, which has exon 2 deleted, encodes a functional AMPD peptide. A much higher percentage of alternatively spliced transcripts are found during differentiation of human myocytes in vitro. Transfection studies with human minigene constructs demonstrate that alternative splicing of the primary transcript of human AMPD1 is controlled by tissue-specific and stage-specific signals. Alternative splicing of exon 2 in individuals who have inherited this defect provides a mechanism for phenotypic rescue and variations in splicing patterns may contribute to the variability in clinical symptoms.

AMP Deaminase↗

Dominantly inherited hyperinsulinism caused by a mutation in the sulfonylurea receptor type 1.

ATP-sensitive potassium channels play a major role in linking metabolic signals to the exocytosis of insulin in the pancreatic beta cell. These channels consist of two types of protein subunit: the sulfonylurea receptor SUR1 and the inward rectifying potassium channel Kir6.2. Mutations in the genes encoding these proteins are the most common cause of congenital hyperinsulinism (CHI). Since 1973, we have followed up 38 pediatric CHI patients in Finland. We reported previously that a loss-of-function mutation in SUR1 (V187D) is responsible for CHI of the most severe cases. We have now identified a missense mutation, E1506K, within the second nucleotide binding fold of SUR1, found heterozygous in seven related patients with CHI and in their mothers. All patients have a mild form of CHI that usually can be managed by long-term diazoxide treatment. This clinical finding is in agreement with the results of heterologous coexpression studies of recombinant Kir6.2 and SUR1 carrying the E1506K mutation. Mutant K(ATP) channels were insensitive to metabolic inhibition, but a partial response to diazoxide was retained. Five of the six mothers, two of whom suffered from hypoglycemia in infancy, have developed gestational or permanent diabetes. Linkage and haplotype analysis supported a dominant pattern of inheritance in a large pedigree. In conclusion, we describe the first dominantly inherited SUR1 mutation that causes CHI in early life and predisposes to later insulin deficiency.

ATP-Binding Cassette Transporters↗

Hepatocarcinogenesis: a polygenic model of inherited predisposition to cancer.

The murine inbred strain C3H provides an experimental model of inherited predisposition to hepatocellular cancer. Hepatocellular neoplastic lesions induced by chemical carcinogens reach a volume 10-100-fold greater in C3H mice than in genetically resistant strains. However, the huge strain differences in tumor size are explained by relatively small differences (10%-30%) in tumor cell kinetics. Genetic linkage experiments in different crosses demonstrated that six unlinked hepatocarcinogen sensitivity (Hcs) and two hepatocarcinogen resistance (Hcr) loci determined quantitative variations in susceptibility to hepatocarcinogenesis. Such results provide the genetic basis for the strain variations in susceptibility to hepatocarcinogenesis and demonstrate a new model of polygenic inheritance of predisposition to cancer.

Animals↗

Pheochromocytomas and ultimobranchial (C-cell) neoplasms in the bull: evidence of autosomal dominant inheritance in the Guernsey breed.

Pheochromocytomas and ultimobranchial (C-cell) neoplasms were diagnosed at a high frequency in a family of Guernsey bulls. The incidence supported the hypothesis of autosomal dominant inheritance of the neoplasms. These two neoplasms also occur in man as multiple endocrine adenomatosis type 2, which has autosomal dominant inheritance.

Adrenal Gland Neoplasms↗