Detection Of Heterozygous Carriers Research Articles

Advances in the treatment of inherited metabolic diseases.

Major advances have been made in the elucidation of the molecular pathologies of inherited metabolic diseases during the past two decades. The clinical and pathophysiologic manifestations have been delineated and the metabolic derangements have been characterized in an ever-increasing number of these myriad disorders.1–2 Sophisticated chemical and enzymatic techniques as well as in vitro tissue culture systems have been developed to identify the specific enzymatic defects in more than 150 of the over 400 catalogued, recessively inherited, inborn errors of metabolism.2 Implementation of these techniques in major centers has made the diagnosis of these disorders a reality. Indeed, the demonstration of the specific enzymatic deficiency has provided for the accurate diagnosis of affected homozygotes or hemizygotes, detection of heterozygous carriers, and the capability to prenatally diagnose and prevent the birth of affected fetuses. However, in spite of these major diagnostic achievements, patients and their families have become increasingly disappointed by the absence of specific therapies for most of these debilitating disorders.

A practical chromogenic procedure for the diagnosis of Krabbe's disease

Krabbe's disease is caused by a deficiency of galactocerebrosidase in organs and tissues. Determinations of galactocerebrosidase activity had required the use of galactocerebroside labeled with radiocarbon or radiohydrogen. These materials are expensive and their use is restricted to laboratories with radioactive counting facilities. An analogue of galactocerebroside, 2-hexadecanoylamino-4-nitrophenyl-ß-D-galactopyranoside, was synthesized. The hydrolysis of this analogue by extracts of tissues and cells from patients with Krabbe's disease is greatly reduced from normal levels. Cultured skin fibroblasts preparations derived from heterozygous carriers of Krabbe's disease have an intermediate level of hydrolytic activity. Thus, the analogue is a reliable chromogenic reagent for the diagnosis of patients with Krabbe's disease and for the detection of heterozygous carriers of the Krabbe trait.

Diagnosis of von Willebrand's disease: A comparative study of diagnostic tests on nine families with von Willebrand's disease and its differential diagnosis from hemophilia and thrombocytopathy

Nine probands with von Willebrand's disease, and their family members, totalling 43 people, were examined. Twenty-seven had a history of bleeding; 29 had an increased factor VIII activity:factor VIII related antigen ratio; 24 had a decreased factor VIII related antigen; 23 had a prolonged bleeding time; 19 had a reduced platelet adhesiveness; 16 had a decreased factor VIII activity; and 14 had an abnormal ristocetin-induced platelet aggregation. Eight members with both normal bleeding time and normal factor VIII activity were found to have other abnormal tests: elevated ratio of factor VIII activity to factor VIII related antigen in seven; decreased factor VIII related antigen in four; and reduced platelet adhesiveness in one. Therefore, ratio of factor VIII activity to factor VIII related antigen and factor VIII related antigen are more sensitive and may be used for the detection of heterozygous carriers of von Willebrand's disease. Although patients with thrombocytopathy may have a prolonged bleeding time, decreased platelet adhesiveness and reduced platelet aggregation by ristocetin, their factor VIII activity, factor VIII related antigen and ratio of factor VIII activity to factor VIII related antigen are normal and their abnormal ristocetin test cannot be corrected by the addition of factor VIII concentrate. Hemophilic subjects and hemophilic carriers, who are deficient in factor VIII activity, usually have a normal bleeding time, normal platelet adhesiveness, and normal ristocetin test. In contrast to patients with von Willebrand's disease, their factor VIII related antigen is normal or slightly increased and their ratio of factor VIII activity to factor VIII related antigen is significantly reduced. We conclude that ratio of factor VIII activity to factor VIII related antigen and factor VIII related antigen are not only more sensitive but also more specific for the diagnosis of von Willebrand's disease.

Enzyme replacement therapy for the sphingolipidoses.

The greatest progress in the field of inheritable disorders during the past decade was made in the understanding and control of lipid storage diseases. Since original demonstrations in 1965 and 1966 of the metabolic defects in Gaucher’s disease (6,7) Niemann-Pick disease (8), Fabry’s disease (9), and metachromatic leukodystrophy (17), specific enzyme deficiencies were demonstrated in ten heritable disorders of lipid metabolism. These discoveries paved the way for the development of facile procedures for the diagnosis of homozygotes, the detection of heterozygous carriers, and the monitoring of pregnancies at risk for any of these diseases (1–4). These applications of basic research endeavors have provided much relief from human anguish and suffering and they are in wide use at this time. However, there still remains much to be done for affected patients and compassionate physicians continue to seek further help in the treatment of hundreds of patients with these diseases. In particular, the therapy of patients with Type I (adult) Gaucher’s disease in whom skeletal involvement causes severe bone and joint pains, and patients with Fabry’s disease with intractable pains in arms and legs and progressive renal impairment deserves intensive attention. During the past three years much of our research efforts have been devoted to these two disorders.

A Practical Chromogenic Procedure for the Detection of Homozygotes and Heterozygous Carriers of Niemann-Pick Disease

Niemann-Pick disease is caused by a deficiency of sphingomyelinase in organs and tissues. Determinations of sphingomyelinase activity had required the use of sphingomyelin labeled with radiocarbon or radiohydrogen. These materials are expensive, and their use is restricted to laboratories with radioactive counting facilities. An analogue of sphingomyelin, 2-hexadecanoylamino-4-nitrophenylphosphorylcholine, was synthesized. This substance is hydrolyzed by highly purified sphingomyelinase, and by sphingomyelinease in extracts of human liver tissue, cultured skin fibroblasts, cultured amniotic cells and washed leukocyte preparations. Extracts of tissues and cells from patients with Niemann-Pick disease Type A do not hydrolyze this compound, whereas heterozygotes and patients with Niemann-Pick disease Type C have an intermediate level of hydrolytic activity. Thus, the analogue is a reliable chromogenic reagent for the diagnosis of patients with Niemann-Pick disease and the detection of heterozygous carriers of the Niemann-Pick trait.

The Lipid Storage Diseases: New Concepts and Control

The nature of the enzymatic defect is now well established in ten inherited disorders of lipid metabolism. This information has provided for the development of facile, sensitive tests using readily available materials such as washed leukocytes or cultured skin fibroblasts for the diagnosis of these disorders; the detection of heterozygous carriers of these traits; and the monitoring of pregnancies at risk for any of these conditions. Recent investigations of enzyme replacement therapy have shown great promise for the treatment of patients with Fabry's disease and those with the adult form of Gaucher's disease. Additional procedures must be developed for successful enzyme replacement in patients where the central nervous system is damaged by the accumulation of lipids.

Lyonization in hemophilia: a cause of error in direct detection of heterozygous carriers.

Lyonization in hemophilia: a cause of error in direct detection of heterozygous carriers.

Genetic Consultations in Neuroophthalmology

The geneticist faced with severe neuroophthalmological conditions should not only establish the prognosis on the basis of probability laws, but also take into consideration the prevailing affective and social situation of these patients and their families.Huntington's chorea, e.g., manifests itself between 30 and 40 years of age, that is to say, when the patients often have already one or more children, who shall be exposed to the threat of becoming affected until rather an advanced age.Among other dominant affections, myotonic dystrophy (Steinert) is discussed, which can nowadays be diagnosed in about 1/3 of cases before the first clinical manifestations, owing to slit-lamp examination and electromyography. Contrary to Huntington's disease, the affection can be detected at an early stage of life, so that the patients may still be dissuaded from having children.In the field of ophthalmological conditions, the genetics of uni- and bilateral retinoblastoma, the three types of retinitis pigmentosa (recessive, dominant, sex-linked), the Lowe's and Waardenburg-Klein syndromes, as well as Tay-Sachs disease, are reviewed. As regards the latter condition, the importance of the discovery of a deficiency of hexosaminidase A is pointed out, since the detection of heterozygous carriers, and even prenatal diagnosis, have now become possible for this disease.

Detection of heterozygous carriers of the Lesch-Nyhan syndrome by electrophoresis of hair root lysates

Mosaicism has been demonstrated for the X-linked enzyme hypoxanthine-guanine phosphoribosyl transferase (HGPRT) in heterozygous carriers of the Lesch-Nyhan syndrome by examining single hair follicles for the activity of HGPRT and adenine phosphoribosyl transferase (APRT) using polyacrylamide gel electrophoresis. The method is useful in the detection of the carrier state and has advantages over methods previously published.

Detection of Tay-Sachs disease heterozygotes by assay of hexosaminidase A in serum and leukocytes

Activity of the enzyme hexosaminidase A was assayed by cellulose acetate electrophoresis in serum and leukocytes of parents of children with Tay-Sachs disease. The activity of the enzyme was lower than normal in both serum and leukocytes of the parents. The data from the serum assay were more consistent than those from the leukocyte assay. This method is applicable for the detection of heterozygous carriers of Tay-Sachs disease. Activity of the enzyme hexosaminidase A was assayed by cellulose acetate electrophoresis in serum and leukocytes of parents of children with Tay-Sachs disease. The activity of the enzyme was lower than normal in both serum and leukocytes of the parents. The data from the serum assay were more consistent than those from the leukocyte assay. This method is applicable for the detection of heterozygous carriers of Tay-Sachs disease.

Genetics and the lipidoses.

AbstractFormal genetic analyses of family data in cases of errors of lipid metabolism are able to distin‐guish monogenic vs. multigenic and nongenetic disorders. These data, together with population data, provide criteria for the homogeneity of cases which can be useful in the interpretation of biochemical findings. The peculiarly elevated incidence of three main genotypes of sphingo‐lipidoses among Ashkenasic Jews has no reason‐able explanation except for heterozygote selection. This inference has strong implications for the biochemist in that it suggests a) the existence of some biochemical abnormality is common among the heterozygotes for these conditions and b) the utility of such a heterozygote abnormality in the defense of the body against some adverse en‐vironmental stress, such as some specific infectious disease.The detection of heterozygous carriers by bio‐chemical means could be important not only for this reason but also as a means for anticipating marriages which may produce a lethal lipidosis. Finally, as long as preventive measures are either imperfect or not practiced, major attention is directed toward therapy, which in turn requires not only more knowledge of the basic defect but awareness of the fact that such knowledge may not be helpful without the development of more advanced devices than those employed in, for ex‐ample, phenylketonuria or galactosemia. The deep‐seated nature of the presumed lesions in the lipidoses seems to require a different type of corrective measure, such as gene replacement or transformation.

The detection of carriers in hereditary myoclonic epilepsy.

SummaryThree cases of hereditary myoclonic epilepsy have been observed among ten siblings in a Negro family. Electroencephalograms of the parents, three normal siblings and two of the three affected siblings have been recorded and all show abnormalities of a similar type. These are of a generalized nature revealing no focal damage. This type of abnormality has been observed in an affected male and two normal siblings by Watson and Denny-Brown.The autosomal recessive mode of inheritance observed in the present study is consistent with the transmission most frequently reported in myoclonic epilepsy. We believe that abnormal electroencephalographic patterns are associated with this gene and that these patterns may be useful in the detection of heterozygous carriers.