Genetic screening: carriers and affected individuals

Family Screening and Genetic Counseling

In this brief chapter, clinically very important topics of family screening and genetic counseling are discussed that are also pivotal in endocrine genetics. Genetic screening makes possible to diagnose a genetic disease at an early stage or to exclude its presence. Family members have to be screened if a heritable disease is diagnosed. Personal consultation with the patient and the relatives is inevitable in every genetically determined disease. The main function of genetic counseling is the transfer of important pieces of information to the patient about the congenital or later-manifesting diseases. This process via the informed consent should give enough information to the patient and the relatives to make decisions about the disease. Genetic data should be considered as special data; therefore the protection of the personal data and the confidentiality obligation should be prevailed intensively. The chief goal of the genetic counseling is the prevention of the conception or the birth of a person who would suffer from a severe genetic disease and/or to present information of the chance for having an affected descendant. If the prevention is not feasible, the alternative aim is to prevent the development of the consequences or to moderate its severity. Genetic counseling has important ethical aspects such as prenatal genetic investigations; hereditary, but treatable, nonlethal diseases; and genetic diseases that manifest late, predominantly in the adulthood.

Maple syrup urine disease: mechanisms and management

Maple syrup urine disease (MSUD) is an inborn error of metabolism caused by defects in the branched-chain α-ketoacid dehydrogenase complex, which results in elevations of the branched-chain amino acids (BCAAs) in plasma, α-ketoacids in urine, and production of the pathognomonic disease marker, alloisoleucine. The disorder varies in severity and the clinical spectrum is quite broad with five recognized clinical variants that have no known association with genotype. The classic presentation occurs in the neonatal period with developmental delay, failure to thrive, feeding difficulties, and maple syrup odor in the cerumen and urine, and can lead to irreversible neurological complications, including stereotypical movements, metabolic decompensation, and death if left untreated. Treatment consists of dietary restriction of BCAAs and close metabolic monitoring. Clinical outcomes are generally good in patients where treatment is initiated early. Newborn screening for MSUD is now commonplace in the United States and is included on the Recommended Uniform Screening Panel (RUSP). We review this disorder including its presentation, screening and clinical diagnosis, treatment, and other relevant aspects pertaining to the care of patients.

Prenatal β-thalassemia carrier screening in Australia: healthcare professionals' perspectives of clinical practice

OBJECTIVE

To gain a better understanding of healthcare professionals' practice and attitudes regarding prenatal β-thalassemia carrier screening in Australia.

METHOD

Qualitative study with semi-structured interviews of healthcare professionals (obstetricians, general practitioners, midwives, genetic counselors, and hematologists) involved in prenatal thalassemia carrier screening in public and private practice.

RESULTS

Twenty-three healthcare providers were interviewed and several themes emerged. Participants described and acknowledged inconsistencies in the β-thalassemia screening processes, such as variability in ordering the tests, communicating the diagnosis, and action taken after diagnosis. They indicated a preference for more structure and valued the importance of screening guidelines but many of those involved in ordering the screening test were unaware of their availability. These healthcare professionals recognized they lacked knowledge regarding the screening process, and many had not undertaken education activities in this area in recent times. There were mixed views about the consent process, particularly at which stage this should be obtained, and what information is provided.

CONCLUSIONS

β-thalassemia screening in Victoria occurs with apparent lack of awareness of guidelines and an acknowledged preference for a more systematic process and educational support. Informed consent was not considered an important component of this screening process.

Adopting orphans: comprehensive genetic testing of Mendelian diseases of childhood by next-generation sequencing

Orphan diseases are individually uncommon but collectively contribute significantly to pediatric morbidity, mortality and healthcare costs. Current molecular testing for rare genetic disorders is often a lengthy and costly endeavor, and in many cases a molecular diagnosis is never achieved despite extensive testing. Diseases with locus heterogeneity or overlapping signs and symptoms are especially challenging owing to the number of potential targets. Consequently, there is immense need for scalable, economical, rapid, multiplexed diagnostic testing for rare Mendelian diseases. Recent advances in next-generation sequencing and bioinformatic technologies have the potential to change the standard of care for the diagnosis of rare genetic disorders. These advances will be reviewed in the setting of a recently developed test for 592 autosomal recessive and X-linked diseases.

[Genetic testing in the context of the revision of the French law on bioethics]

This article focuses on six questions raised by genetic testing in human: (1) the use of genetic tests, (2) information given to relatives of patients affected with genetic disorders, (3) prenatal and preimplantatory diagnosis for late onset genetic diseases and the use of pangenomic tests in prenatal diagnosis, (4) direct-to-consumer genetic testing, (5) population screening in the age of genomic medicine and (6) incidental findings when genetic testing are used.

High incidence of later-onset fabry disease revealed by newborn screening

The classic phenotype of Fabry disease, X-linked alpha -galactosidase A (alpha -Gal A) deficiency, has an estimated incidence of approximately 1 in 50,000 males. The recent recognition of later-onset variants suggested that this treatable lysosomal disease is more frequent. To determine the disease incidence, we undertook newborn screening by assaying the alpha-Gal A activity in blood spots from 37,104 consecutive Italian male neonates. Enzyme-deficient infants were retested, and "doubly screened-positive" infants and their relatives were diagnostically confirmed by enzyme and mutation analyses. Twelve (0.03%) neonates had deficient alpha-Gal A activities and specific mutations, including four novel missense mutations (M51I, E66G, A73V, and R118C), three missense mutations (F113L, A143T, and N215S) identified previously in later-onset patients, and one splicing defect (IVS5(+1G-->T)) reported in a patient with the classic phenotype. Molecular modeling and in vitro overexpression of the missense mutations demonstrated structures and residual activities, which were rescued/enhanced by an alpha-Gal A-specific pharmacologic chaperone, consistent with mutations that cause the later-onset phenotype. Family studies revealed undiagnosed Fabry disease in affected individuals. In this population, the incidence of alpha-Gal A deficiency was 1 in approximately 3,100, with an 11 : 1 ratio of patients with the later-onset : classic phenotypes. If only known disease-causing mutations were included, the incidence would be 1 in approximately 4,600, with a 7 : 1 ratio of patients with the later-onset : classic phenotypes. These results suggest that the later-onset phenotype of Fabry disease is underdiagnosed among males with cardiac, cerebrovascular, and/or renal disease. Recognition of these patients would permit family screening and earlier therapeutic intervention. However, the higher incidence of the later-onset phenotype in patients raises ethical issues related to when screening should be performed--in the neonatal period or at early maturity, perhaps in conjunction with screening for other treatable adult-onset disorders.