Localization of the human prealbumin gene to 18p11.1-q12.3 by gene dose effect study of Southern blot hybridization

Transthyretin mutagenesis: impact on amyloidogenesis and disease

Transthyretin (TTR), a homotetrameric protein found in plasma, cerebrospinal fluid, and the eye, plays a pivotal role in the onset of several amyloid diseases with high morbidity and mortality. Protein aggregation and fibril formation by wild-type TTR and its natural more amyloidogenic variants are hallmarks of ATTRwt and ATTRv amyloidosis, respectively. The formation of soluble amyloid aggregates and the accumulation of insoluble amyloid fibrils and deposits in multiple tissues can lead to organ dysfunction and cell death. The most frequent manifestations of ATTR are polyneuropathies and cardiomyopathies. However, clinical manifestations such as carpal tunnel syndrome, leptomeningeal, and ocular amyloidosis, among several others may also occur. This review provides an up-to-date listing of all single amino-acid mutations in TTR known to date. Of approximately 220 single-point mutations, 93% are considered pathogenic. Aspartic acid is the residue mutated with the highest frequency, whereas tryptophan is highly conserved. "Hot spot" mutation regions are mainly assigned to β-strands B, C, and D. This manuscript also reviews the protein aggregation models that have been proposed for TTR amyloid fibril formation and the transient conformational states that convert native TTR into aggregation-prone molecular species. Finally, it compiles the various in vitro TTR aggregation protocols currently in use for research and drug development purposes. In short, this article reviews and discusses TTR mutagenesis and amyloidogenesis, and their implications in disease onset.

Contemporary Insights Into the Genetics of Hypertrophic Cardiomyopathy: Toward a New Era in Clinical Testing?

Genetic testing for hypertrophic cardiomyopathy (HCM) is an established clinical technique, supported by 30 years of research into its genetic etiology. Although pathogenic variants are often detected in patients and used to identify at-risk relatives, the effectiveness of genetic testing has been hampered by ambiguous genetic associations (yielding uncertain and potentially false-positive results), difficulties in classifying variants, and uncertainty about genotype-negative patients. Recent case-control studies on rare variation, improved data sharing, and meta-analysis of case cohorts contributed to new insights into the genetic basis of HCM. In particular, although research into new genes and mechanisms remains essential, reassessment of Mendelian genetic associations in HCM argues that current clinical genetic testing should be limited to a small number of validated disease genes that yield informative and interpretable results. Accurate and consistent variant interpretation has benefited from new standardized variant interpretation guidelines and innovative approaches to improve classification. Most cases lacking a pathogenic variant are now believed to indicate non-Mendelian HCM, with more benign prognosis and minimal risk to relatives. Here, we discuss recent advances in the genetics of HCM and their application to clinical genetic testing together with practical issues regarding implementation. Although this review focuses on HCM, many of the issues discussed are also relevant to other inherited cardiac diseases.

Familial amyloidotic polyneuropathy and transthyretin

There has been much progress in our understanding of transthyretin (TTR)-related amyloidosis including familial amyloidotic polyneuropathy (FAP), senile systemic amyloidosis and its related disorders from many clinical and experimental aspects. FAP is an inherited severe systemic amyloidosis caused by mutated TTR, and characterized by amyloid deposition mainly in the peripheral nervous system and the heart. Liver transplantation is the only available treatment for the disease. FAP is now recognized not to be a rare disease, and to have many variations based on genetical and biochemical variations of TTR. This chapter covers the recent advances in the clinical and pathological aspects of, and therapeutic approaches to FAP, and the trend as to the molecular pathogenesis of TTR.

Identification of a marker chromosome as inv dup(15) by molecular analysis

The origin of an extra marker chromosome in a patient with mental retardation and intractable epilepsy was ascertained by DNA analysis. Gene dose and restriction fragment length polymorphism (RFLP) studies of D15S9 proved that the patient was tetrasomic for the gene and that the extra chromosome was of maternal origin. On the basis of the molecular findings, further detailed GTG-banded chromosome analysis interpreted the marker chromosome as inv dup(15)(pter----q14::q14----pter). The clinical manifestations of the patient are consistent with those of the patients previously described.

Satellited chromosome 9 in a boy with multiple anomalies

A 5-year-old boy with multiple congenital anomalies showed a satellited long-arm chromosome 9, a previously undescribed abnormality. Various banding analyses of his chromosomes and those of his parents indicated that a reciprocal translocation, t(9;22)(q34.3;q11.21), occurred in the father's gonad, and one of the translocation chromosomes was then transmitted to the patient. Thus, the patient's karyotype was interpreted as 46,XY,-9,+psudic(9),t(9;22)(q34.3;q11.21). He showed several features similar to those of the Williams syndrome. The gene(s) responsible for the syndrome thus could be at either 9q34.3-qter or 22pter-q11.2. Southern blot analysis of the patient's DNA indicated the presence of two copies of the argininosuccinate synthetase gene which had been assigned to 9q34.1-qter. In view of the fact that the 9q34.3-qter segment is monosomic in the patient, the gene locus was deduced to be at 9q34.1-q34.2 segment.

Prenatal DNA analysis in four embryos/fetuses at risk of 21-hydroxylase deficiency

Prenatal diagnosis of 21-hydroxylase deficiency (21-OHD) in two unrelated embryos and two fetuses was attempted with the Southern hybridization method using the 21-hydroxylase (21-OHase) complementary DNA as a probe. The two embryos whose genomic DNA was extracted from their chorionic villi both had four TaqI fragments (3.7 kb, 3.2 kb, 2.4 kb and 2.3 kb) identical to those of their respective parents and normal controls, while the DNA from each proband of these two families lacked with the 3.7 kb and the 2.3 kb fragments corresponding to the functional 21-OHase gene (21-OHase B gene). These findings indicated that none of the embryos examined were deletion homozygotes for the 21-OHase B gene. In the two fetuses, only amniotic fluid cells were available for prenatal diagnosis. The results of Southern hybridization analysis were uninformative since all family members, including the probands and fetuses, had all four TaqI fragments. Linkage studies between 21-OHD and human leukocyte antigen (HLA) haplotypes and those between the disease and restriction fragment length polymorphisms of the 4th complement gene revealed that the fetus of one family was normal. The other fetus could not be diagnosed because a recombination between the class I HLA and the 21-OHD loci had occurred in this family.

Origin of the extra chromosome in trisomy 18. A study on five patients using a restriction fragment length polymorphism

The parental origin of an extra chromosome in five patients with trisomy 18 was traced using a restriction fragment length polymorphism (RFLP) of the human prealbumin (PA) gene, localized to 18p11.1-q12.1, as a genetic marker. MspI digests of the genomic DNAs of the five patients, their parents and normal controls were hybridized with the PA-cDNA. Densitometric analysis on the gene dose of the polymorphic fragments of these patients revealed that three had originated from a maternal meiotic error. The other two patients were uninformative for the parental origin of trisomy 18. Our results indicate that nondisjunctional errors leading to trisomy 18 may occur predominantly at the maternal meiosis, consistent with the results of previous studies on the parental origin of trisomies 21 and 13.