Homozygous Inheritance Research Articles

A hereditary bleeding disorder of dogs caused by a lack of platelet procoagulant activity

We have discovered a novel canine hereditary bleeding disorder with the characteristic features of Scott syndrome, a rare defect of platelet procoagulant activity. Affected dogs were from a single, inbred colony and experienced clinical signs of epistaxis, hyphema, intramuscular hematoma, and prolonged bleeding with cutaneous bruising after surgery. The hemostatic abnormalities identified were restricted to tests of platelet procoagulant activity, whereas platelet count, platelet morphology under light microscopy, bleeding time, clot retraction, and platelet aggregation and secretion in response to thrombin, collagen, and adenosine diphosphate stimulation were all within normal limits. Washed platelets from the affected dogs demonstrated approximately twice normal clotting times in a platelet factor 3 availability assay and, in a prothrombinase assay, generated only background levels of thrombin in response to calcium ionophore, thrombin, or combined thrombin plus collagen stimulation. While platelet phospholipid content was normal, flow cytometric analyses revealed diminished phosphatidylserine exposure and a failure of microvesiculation in response to calcium ionophore, thrombin, and collagen stimulation. Pedigree studies indicate a likely homozygous recessive inheritance pattern of the defect. These findings confirm the importance of platelet procoagulant activity for in vivo hemostasis and provide a large animal model for studying agonist-induced signal transduction, calcium mobilization, and effector pathways involved in the late platelet response of transmembrane phospholipid movement and membrane vesiculation.

Compound heterozygosity and nonsense mutations in the alpha(1)-subunit of the inhibitory glycine receptor in hyperekplexia.

The alpha(1)-inhibitory glycine receptor is a ligand-gated chloride channel composed of three ligand-binding alpha1-subunits and two structural beta-subunits that are clustered on the postsynaptic membrane of inhibitory glycinergic neurons. Dominant and recessive mutations in GLRA1 subunits have been associated with a proportion of individuals and families with startle disease or hyperekplexia (MIM: 149400). Following SSCP and bi-directional di-deoxy fingerprinting mutational analysis of 22 unrelated individuals with hyperekplexia and hyperekplexia-related conditions, we report further novel missense mutations and the first nonsense point mutations in GLRA1, the majority of which localise outside the regions previously associated with dominant, disease-segregating mutations. Population studies reveal the unique association of each mutation with disease, and reveals that a proportion of sporadic hyperekplexia is accounted for by the homozygous inheritance of recessive GLRA1 mutations or as part of a compound heterozygote.

Neutrophil-specific granule deficiency: homozygous recessive inheritance of a frameshift mutation in the gene encoding transcription factor CCAAT/enhancer binding protein–ε

AbstractNeutrophil-specific granule deficiency (SGD) is a rare congenital disorder. The neutrophils of individuals with SGD display atypical bi-lobed nuclei, lack expression of all secondary and tertiary granule proteins, and possess defects in chemotaxis, disaggregation, receptor up-regulation, and bactericidal activity, resulting in frequent and severe bacterial infections. Previously, a homozygous mutation in theCCAAT/enhancer binding protein–ε (C/EBPε) gene was reported for one case of SGD. To substantiate the role of C/EBPε in the development of SGD and elucidate its mechanism of inheritance, the mutational status of the gene was determined in a second individual. An A-nucleotide insertion in the coding region of the C/EBPε gene was detected. This mutation completely abolished the predicted translation of all C/EBPε isoforms. Microsatellite and nucleotide sequence analyses of the C/EBPε locus in the parents of the proband indicated that the disorder may have resulted from homozygous recessive inheritance of the mutant allele from an ancestor shared by both parents. The mutant C/EBPε32 protein localized in the cytoplasm rather than the nucleus and was unable to activate transcription. Consistent with this, a significant decrease in the levels of the messenger RNAs (mRNAs) encoding the secondary granule protein human 18-kd cationic antimicrobial protein (hCAP-18)/LL-37 and the primary granule protein bactericidal/permeability-increasing protein were observed in the patient. The hCAP-18 mRNA was induced by overexpression of C/EBPε32 in the human myeloid leukemia cell line, U937, supporting the hypothesis that C/EBPε is a key regulator of granule gene synthesis. This study strongly implicates mutation of theC/EBPε gene as the primary genetic defect involved in the development of neutrophil SGD and defines its mechanism of inheritance.

The emerging understanding of sickle cell disease.

The emerging understanding of sickle cell disease.

What are the implications of sickle cell anaemia?

Sickle Cell Trait is common in certain populations. The vast majority of individuals who possess combinations of these genes which cause variations in haemoglobin are asymptomatic. However, despite advances in treatment, health problems associated with homozygous inheritance can result in work-related performance issues. Such cases require individual risk assessments in relation to their jobs when considering fitness for work, rehabilitation and prevention of symptoms.

Homozygosity and Linkage-Disequilibrium Mapping of the Syndrome of Congenital Hypoparathyroidism, Growth and Mental Retardation, and Dysmorphism to a 1-cM Interval on Chromosome 1q42-43

The syndrome of hypoparathyroidism associated with growth retardation, developmental delay, and dysmorphism (HRD) is a newly described, autosomal recessive, congenital disorder with severe, often fatal consequences. Since the syndrome is very rare, with all parents of affected individuals being consanguineous, it is presumed to be caused by homozygous inheritance of a single recessive mutation from a common ancestor. To localize the HRD gene, we performed a genomewide screen using DNA pooling and homozygosity mapping for apparently unlinked kindreds. Analysis of a panel of 359 highly polymorphic markers revealed linkage to D1S235. The maximum LOD score obtained was 4.11 at a recombination fraction of 0. Analysis of three additional markers-GGAA6F06, D1S2678, and D1S179-in a 2-cM interval around D1S235 resulted in LOD scores >3. Analysis of additional chromosome 1 markers revealed evidence of genetic linkage disequilibrium and place the HRD locus within an approximately 1-cM interval defined by D1S1540 and D1S2678 on chromosome 1q42-43.

Homocysteine and risk of premature coronary heart disease. Evidence for a common gene mutation.

Plasma homocysteine levels are modulated by nutritional and genetic factors, among which is the enzyme methylenetetrahydrofolate reductase (MTHFR). A common defective (thermolabile) variant of this enzyme is causally associated with elevated plasma homocysteine, itself an independent risk factor for coronary heart disease. To examine the hypothesis that the allele (T) that codes for the thermolabile defect increases the risk of coronary heart disease, we studied 111 patients with clinical and objective investigational evidence of coronary heart disease and 105 control subjects. The frequencies of the thermolabile defect (T) in patients and control subjects were measured, and the prevalence of elevated plasma total homocysteine according to genotype was assessed. The frequency of the defective allele was higher in patients than in control subjects with an OR of 1.6 (95% CI, 1.1 to 2.4; P = .02). The OR in the coronary heart disease group for the homozygous TT genotype was 2.9 (95% CI, 1.2 to 7.2; P = .02); 17% of patients and 7% of control subjects had the TT genotype. Plasma total homocysteine levels were significantly associated with disease status, a relationship that matched the strength of the association between disease and homozygous inheritance of the defective enzyme. Homozygotes for the defective allele (T) are at increased risk of premature coronary heart disease. MTHFR, which modulates basal plasma homocysteine concentration, is folate dependent, and dietary supplementation or fortification with folic acid may reduce plasma homocysteine levels and consequent coronary risk in a significant proportion of the general population.

Inheritance and testicular cancer.

Statistical analysis of published data on the age of onset of germ cell tumours of the testis and of the prevalence of bilateral disease in familial and general cases suggest the following: 1. Patients with bilateral disease carry the same genetic predisposition as familial cases. 2. Males with the hereditary predisposition develop none, unilateral or bilateral tumours in the proportions 55%, 38% and 7% respectively. 3. One-third of all testis cancer patients are genetically predisposed to the disease. 4. The 2.2% risk to brothers of cases as reported elsewhere can be accounted for by the homozygous (recessive) inheritance of a single predisposing gene.

Enzymic analysis of soya beans lacking lipoxygenases

AbstractThe homozygous inheritance of recessive alleles for lipoxygenase, ‐L1, ‐L2 and ‐L3 incorporated into a commercial soya bean seed line, IAC 8, was evaluated. The activity of each isozyme, determined by spectrophotometry demonstrated a very low activity for the mutant ‐L1 and respective progeny and a low activity for ‐L2, ‐L3 and their progenies. The methodology employed was shown to be a reliable and rapid method when evaluating lipoxygenase from crops.

Localization of a novel chromosome 7 locus that suppresses development of N‐methyl‐N‐nitrosourea—induced murine thymic lymphomas

N-Methyl-N-nitrosourea (MNU) is a potent carcinogen that causes the development of murine thymic lymphomas. MNU-induced tumor incidence varies considerably among different inbred mouse strains. In particular, the AKR strain is highly susceptible, whereas the C57L strain is highly resistant to MNU-induced lymphoma formation. Crosses between AKR and C57L mice were established to investigate the genetic basis for the differential susceptibility of these inbred strains. A strong association between MNU-induced lymphoma development and coat color was observed in (AKR x C57)F2 and AKR x (AKR x C57)F1 progeny such that albino mice developed a higher tumor incidence than nonalbino animals. These data suggest that a locus on chromosome 7 influences tumor development. Analysis of four additional polymorphic loci (D7Rp2, Fes, Hbb, and Int-2) on chromosome 7 in AKR x (AKR x C57)F1 backcross mice revealed a significant linkage between high tumor incidence and homozygous inheritance of AKR alleles at the albino (tyrosinase) and Hbb loci. Thus, inheritance of at least one C57L allele at the albino or Hbb loci was associated with protection against MNU-induced lymphoma development. There was no association between tumor incidence and genotype at the D7Rp2, Fes, or Int-2 loci. Taken together, the data suggest that whereas C57L mice contain a dominant tumor suppressor gene on chromosome 7, in the AKR strain both alleles at this locus are defective resulting in enhanced susceptibility to MNU-induced lymphomagenesis.

An unusual case of variegate porphyria with possible homozygous inheritance

We report an unusual case of variegate porphyria in a young girl with epilepsy, mental retardation and premature adrenarche. Symptoms of porphyria commenced about the age of 12 years and death occurred about 18 months later. The patient had very low protoporphyrinogen oxidase activity in her cultured fibroblasts. Both parents had half the normal activity of this enzyme in lymphocytes and are heterozygous for the abnormal gene for variegate porphyria. Therefore, it is possible that the patient was a homozygous variant. Anticonvulsant therapy and low hepatic 5 alpha reductase activity were probably other contributing factors to the severity of the condition in this patient.

Ribonuclease A cleavage combined with the polymerase chain reaction for detection of the Z mutation of the alpha-1-antitrypsin gene.

Homozygous inheritance of the Z mutation (exon V, Glu342GAG----Lys342AAG), the most common cause of alpha-1-antitrypsin (alpha 1AT) deficiency, is associated with a high risk for emphysema and liver disease. This study presents a rapid and accurate approach to definitive genotypic diagnosis of the Z homozygous state using a combination of polymerase chain reaction amplification of exon V of the alpha 1AT gene and ribonuclease cleavage of an exon V-specific antisense RNA probe. Taking advantage of the concept that ribonuclease A will cleave at points of mismatch of RNA-DNA hybrids, a 0.79 kb antisense RNA probe was designed with complementarity to the sense strand of exon V of the alpha 1AT gene (the site of the Z mutation) along with small regions of the 5' and 3' flanking sequences. After amplification of exon V of the alpha 1AT gene from genomic DNA by the polymerase chain reaction, the amplified DNA was analyzed by hybridization to a 32P-labeled exon V antisense RNA probe followed by digestion with RNase A. Any substitution mutations resulting in DNA-RNA mismatch were detected by evaluation with polyacrylamide gel electrophoresis under denaturing conditions followed by autoradiography (expected fragment lengths: 0.33 kb when the exon V probe hybridized to the normal amplified genomic DNA, 0.25 and 0.08 kb fragments when the exon V probe hybridized to the amplified genomic DNA with the Z mutation). Double-blinded evaluation of genomic DNA of 36 individuals (phenotypes MM n = 14, MZ n = 5, ZZ n = 16, ZNull n = 1; included among the "M" alleles were representatives of all the major normal M alleles) demonstrated definitive diagnosis of the Z mutation with absolute specificity for all 36 specimens, i.e., ZZ homozygotes, MZ heterozygotes, and normals were all detected accurately. This approach should be useful not only for screening for the Z mutation of the alpha 1AT gene, but by this type of analysis, mutational alterations of the alpha 1AT gene can be screened for without prior knowledge of the sequence changes and without complex cloning and sequencing methods.

Molecular Basis of the Liver and Lung Disease Associated with the α1-Antitrypsin Deficiency Allele Mmalton

Abstract Alpha 1-Antitrypsin (alpha 1AT) deficiency is characterized by reduced serum levels of alpha 1AT and a risk for the development of emphysema and liver disease. However, whereas there is an increased risk for emphysema associated with at least 10 alpha 1AT deficiency and null alleles, the hepatic disease is observed only in a subset of these alleles, suggesting that it is not the reduced serum levels of alpha 1AT per se which cause the liver disease. The present study characterizes the alpha 1AT deficiency allele Mmalton, an allele that like the common Z deficiency mutation (Glu342----Lys) is associated with both alpha 1AT deficiency and hepatic disease. Capitalizing on the identification of the homozygous inheritance of the rare Mmalton alpha 1AT deficiency allele, it was demonstrated that although caused by a very different mutation, the Mmalton allele shares with the Z allele the association of liver disease with the same type of abnormalities of alpha 1AT biosynthesis. Cloning of the Mmalton gene and sequence analysis demonstrated that it differs from the normal alpha 1AT M2 allele by deletion of the entire codon (TTC) for residue Phe52. Liver biopsy of the Mmalton homozygote revealed inflammation, mild fibrosis, and intrahepatocyte accumulation of alpha 1AT. Evaluation of de novo alpha 1AT biosynthesis in alpha 1AT-synthesizing cells of this individual demonstrated normal levels of alpha 1AT mRNA transcripts but abnormal intracellular accumulation of newly synthesized alpha 1AT at the level of the rough endoplasmic reticulum with consequent reduced alpha 1AT secretion. Finally, retroviral gene transfer of a normal alpha 1AT cDNA and an alpha 1AT cDNA with the Mmalton Phe52 deletion into murine cells demonstrated that the Mmalton cells reproduced the abnormal accumulation of newly synthesized alpha 1AT, thus directly demonstrating that the deletion mutation is responsible for the intracellular accumulation of the newly synthesized alpha 1AT. Thus, not only is the liver disease associated with alpha 1AT deficiency restricted to a subset of alpha 1AT deficiency alleles, it appears to be restricted to those alleles associated with intracellular accumulation of newly synthesized alpha 1AT, suggesting that it is the abnormal intrahepatocyte alpha 1AT accumulation which incites the liver injury.

Repair of the secretion defect in the Z form of alpha 1-antitrypsin by addition of a second mutation.

Homozygous inheritance of the Z-type mutant form of the alpha 1-antitrypsin (alpha 1AT) gene results in the most common form of alpha 1AT deficiency, a human hereditary disease associated with a high risk for the development of emphysema and an increased incidence of neonatal hepatitis. The alpha 1AT-synthesizing cells of individuals with the Z gene have normal alpha 1AT messenger RNA levels, but alpha 1AT secretion is markedly reduced secondary to accumulation of newly synthesized alpha 1AT in the rough endoplasmic reticulum. Crystallographic analysis of alpha 1AT predicts that in normal alpha 1AT, a negatively charged Glu342 is adjacent to positively charged Lys290. Thus the Glu342----Lys342 Z mutation caused the loss of a normal salt bridge, resulting in the intracellular aggregation of the Z molecule. The prediction was made that a second mutation in the alpha 1AT genet that changed the positively charged Lys290 to a negatively charged Glu290 would correct the secretion defect. When the second mutation was added to the Z-type complementary DNA, the resulting gene directed the synthesis and secretion of amounts of alpha 1AT similar to that directed by the normal alpha 1AT complementary DNA in an in vitro eukaryotic expression system. This suggests the possibility that a human hereditary disease can be corrected by inserting an additional mutation in the same gene.

Alpha1-Antitrypsin Deficiency: Heterozygosity, Intermediate Levels, and Pulmonary Disease

Homozygous inheritance of alpha1 antitrypsin deficiency results in very low serum trypsin inhibitory capacity (TIC) and is associated with a high prevalence of a characteristic form of pulmonary emphysema. Heterozygous inheritance of the trait results in intermediate serum TIC values, but may be difficult to identify with certainty by serologic methods. Because of this, the relation between the heterozygous state, serum TIC values and the development of lung disease is difficult to assess. In a previous report we attempted to evaluate the prevalence of intermediate antitrypsin levels in a population of patients with pulmonary disease. In contrast, the present paper correlates the prevalence of pulmonary disease and antitrypsin levels in three different, carefully selected populations.

BEHAVIOR IN PHENYLKETONURIA; CASE WITH SCHIZOPHRENIA.

Perhaps no inherited disorder has been evaluated more thoroughly, nor demonstrated more decidedly gene-enzyme specificity dependent on specific environmental conditions and stimulus, than phenylketonuria. Yet many questions remain unanswered, one of the important of these, being specific behavioral aspects of the disease, if any, and their biopsychogenesis. Discovered in 1934 by Dr. Asbjörn Fölling of Oslo, with the help of a perspicacious Norwegian mother who noted a peculiar odor from urine of two of her offspring, phenylketonuria has now become a preventable form of mental retardation.⁸Approximately 700 cases have been mentioned in the literature which abounds with articles concerning various aspects of the disease. The abnormality, the result of homozygous recessive autosomal inheritance^6,21occurs once per 25,000 to 40,000 births in the United States,²¹or in a ratio of 2 to 6 per 100,000 population,^21,37accounting for 0.6%

Dental Bone Changes Occurring in Sickle-Cell Diseases and Abnormal Hemoglobin Traits

Since the discovery by Pauling and his co-workers of the abnormal hemoglobin associated with sickling of the erythrocytes (1), and by others of still different hemoglobin abnormalities, it has become possible to make a precise genetic diagnosis of a variety of congenital hemolytic disorders. By use of relatively simple technics of electrophoresis of hemoglobin, the presence of sickle hemoglobin (S), hemoglobin C (2), hemoglobin D (3), hemoglobin E (4), and hemoglobin G (5) can be detected and easily differentiated from the normal. Clinical experience with patients having these abnormal hemoglobins suggests that each responsible gene acts as a simple mendelian dominant and that each is probably allelic with the determinant for normal hemoglobin. In such circumstances one would expect that an individual might inherit any combination of two of these abnormal genes and that the clinical manifestations of such inheritance would be represented by a modified expression of each. Examples of some of the possible combinations have been encountered and various observations suggest that the clinical pattern of each such genetic disorder is indeed determined by the features of the combined genes. Those abnormal hemoglobin states which have been recognized are sickle-cell trait, hemoglobin C, D, E, and G traits, homozygous sickle inheritance (sickle-cell anemia), homozygous hemoglobin C inheritance (hemoglobin C disease) (6), homozygous hemoglobin E disease (7), and combinations of sickle and hemoglobin C, sickle and hemoglobin D, sickle and hemoglobin E, and sickle and hemoglobin G. Suggested nomenclature (8) for these disorders is given in Table I. Gene frequencies for S and C hemoglobins are relatively high in the Negro population. Hemoglobins D, E, and G, on the other hand, are apparently quite rare. Still other hemolytic disorders may result from the inheritance of a single gene for an abnormal hemoglobin and a determinant for other red-cell abnormalities, Examples of such combinations that have been encountered are sickle-cell thalassemia (9), sickle-cell hereditary sphero-cytosis (10), and hemoglobin-C thalassemia (11). Despite the number of these often interrelated congenital hemolytic states, a precise genetic diagnosis can often be easily made by the use of filter paper electrophoresis of the hemoglobin and examination of the blood smear. On clinical grounds alone, even the differentiation between sickle-cell trait and sickle-cell anemia may at times be exceedingly difficult. Establishing a precise diagnosis becomes important when it is realized that the prognosis of the various genetic disorders differs greatly. It now seems clear that sickle-cell anemia, which results from homozygosity for the sickling character, is almost invariably a severe hemolytic disorder. On the other hand, the variant forms of sicklemia are frequently mild and may have no obvious clinical expression.