Prenatal diagnosis. The era of molecular biology

The advent of molecular genetic engineering has major implications in the diagnosis of genetic diseases by allowing a direct approach of the gene. The purpose of this article is to recall the techniques of molecular biology and to survey their potential and their applications which affect several fields of medical genetics: direct diagnosis of point mutations and deletions, indirect diagnosis by polymorphic linkage, indirect diagnosis of X linked recessive diseases (diagnosis of female carriers or recent mutations, prenatal diagnosis), autosomal recessive diseases (21 hydroxylase deficiency and cystic fibrosis) and autosomal dominant diseases, and finally diagnosis of sex and of chromosomal abnormalities.     

Recent advances in chromosome breakage syndromes and their diagnosis

Chromosome instability is a characteristic cytogenetic feature of a number of genetically determined disorders collectively called as the chromosome breakage syndromes or DNA-repair disorders. They are characterized by susceptibility to chromosomal breakages, increased frequency of breaks and interchanges occurring either spontaneously or following exposure to various DNA-damaging agents. These diseases are a group of genetic disorders sharing a number of features. They are all autosomal recessive, show an increased tendency for chromosomal aberrations and to develop malignancies. The principal diseases in this group having a diverse etiology and clinical manifestations include Fanconi anemia (FA), ataxia telangiectasia (AT), Nijmegen breakage syndrome (NBS), Bloom syndrome (BS), xeroderma pigementosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). The underlying defect in these syndromes is the inability to repair a particular type of DNA damage. A number of repair disorder phenotypes are caused by more than one gene. The diagnosis of these syndromes is made by the characteristic clinical features specific to each disease, but the definitive diagnosis is achieved by laboratory investigations such as cytogenetic, biochemical and molecular methods. The importance of prenatal diagnosis and our experience are discussed in this article.     

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??Abstracts??Familial growth hormone deficiency is caused by genetic mutations and has three inherited modes: autosomal recessive, autosomal dominant and X-linked recessive. Genetic diagnosis is based on detailed history, a clear clinical phenotype and rational application of molecular biology methods.     

家族性生长激素缺乏症的诊断思路

家族性生长激素缺乏症是由遗传基因变异引起的,可分为常染色体隐性遗传、常染色体显性遗传、X染色体隐性遗传等模式。仔细采集病史、明确临床表型、合理应用分子生物学方法进行基因学诊断是明确遗传类型及找到相关突变基因的关键。     

Alterations of neonatal thyroid function

Recent progress has been made in understanding the pathogenesis of neonatal thyroid disorders. Autosomal recessive inheritance of mutations of the thyroid peroxidase and thyroglobulin genes has been described in some patients with congenital hypothyroidism (CH) and a family history of CH. Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis. These discoveries are important for patients with CH diagnosed by neonatal screening, as these patients will have normal fertility. The molecular genetic analysis of mutations of the TSH gene in patients with familial and sporadic cases of isolated central CH, who are missed by TSH screening programmes, now enables rapid diagnosis and appropriate therapy in the neonate. In newborn infants with severe non-autoimmune hyperthyroidism, autosomal dominant gain-of-function mutations in the TSH receptor gene have been demonstrated. In these patients, molecular genetic studies are extremely helpful in therapeutic decision making, as early thyroid ablation is the only effective treatment that avoids the sequelae of long-term hyperthyroidism. Molecular genetic studies are therefore useful in the diagnostic work-up of neonatal thyroid alterations.     

Genetic causes of nonsyndromic hearing loss

Explosive progress is being made in genetic studies of hearing and deafness from the clinical and basic research perspectives. Greater than half of hearing loss is estimated to have a genetic basis. Recent studies of hearing and deafness have identified a dozen genes that cause nonsyndromic hearing disorders. Deafness can be inherited in an autosomal recessive, autosomal dominant, X-linked, or mitochondrial manner. Mutations in one gene, connexin 26 (encoding the gap junction protein beta 2), may be responsible for half of all autosomal recessive nonsyndromic deafness. With new mandates for hearing screening programs for newborns in many states, for the first time, the new information on the genetics of hearing loss can be used to diagnose the cause of hearing loss in some children and to understand better the molecular biology of hearing.     

The limb-girdle muscular dystrophies: diagnostic guidelines.

At least 11 different disorders can be recognized to be genetically distinct within the group of muscle diseases known as the limb-girdle muscular dystrophies. Direct gene or protein based tests are available to confirm the diagnosis in one autosomal dominant and six autosomal recessive forms. In these disorders, therefore, a definition based on molecular pathology is becoming possible. Clinical studies in the genetically defined subgroups may also help to determine phenotypic correlates for the various diseases. An integrated approach to diagnosis in this group, based on clinical observations supported by the result of genetic and protein studies, is likely to provide the optimum level of information.     

Alterations of neonatal thyroid function

Grüters A, Krude H, Biebermann H, Liesenkötter KP, Schöneberg T, Gudermann T. Alterations of neonatal thyroid function. Acta Pædiatr 1999; Suppl 428: 17–22. Stockholm. ISSN 0803–5326
Recent progress has been made in understanding the pathogenesis of neonatal thyroid disorders. Autosomal recessive inheritance of mutations of the thyroid peroxidase and thyroglobulin genes has been described in some patients with congenital hypothyroidism (CH) and a family history of CH. Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis. These discoveries are important for patients with CH diagnosed by neonatal screening, as these patients will have normal fertility. The molecular genetic analysis of mutations of the TSH gene in patients with familial and sporadic cases of isolated central CH, who are missed by TSH screening programmes, now enables rapid diagnosis and appropriate therapy in the neonate. In newborn infants with severe non-autoimmune hyperthyroidism, autosomal dominant gain-of-function mutations in the TSH receptor gene have been demonstrated. In these patients, molecular genetic studies are extremely helpful in therapeutic decision making, as early thyroid ablation is the only effective treatment that avoids the sequelae of long-term hyperthyroidism. Molecular genetic studies are therefore useful in the diagnostic work-up of neonatal thyroid alterations. □ Congenital hypothyroidism, molecular pathogenesis, neonatal hyperthyroidism     

Morphometric Studies of Cystic and Tubulointerstitial Kidney Diseases with Hepatic Fibrosis in Children

Portal tract fibrosis with biliary ductular enlargement or proliferation occurs in a number of genetic diseases that have cystic or tubulointerstitial renal lesions. These include some with renal cystic disease such as autosomal recessive diseases (e.g., infantile polycystic disease, juvenile polycystic disease, and Meckel's syndrome), autosomal dominant diseases (e.g., adult polycystic disease), and, rarely, tuberose sclerosis and dominant glomerulocystic disease. Portal tract fibrosis with biliary enlargement and proliferation occurs also with tubulointerstitial kidney diseases. These probably include at least three disorders in the category nephronophthisis-congenital hepatic fibrosis (one autosomal recessive disease and two either autosomal or X-linked recessive diseases) plus Jeune's syndrome (the tubulointerstitial diseases Fanconi's familial nephronophthisis and anti-tubular membrane antibody disease do not regularly cause hepatic fibrosis). Morphometric data on ratios of bile ductules to connective tissue in hepatic portal tracts show high values for infantile polycystic disease (mean, 0.616) compared to lower values for juvenile polycystic disease (mean, 0.286). That the cystic renal lesions of the first two diseases differ in type and time course is known. Similar data on ratios of glomeruli plus tubules to connective tissue in renal cortices and of tubules to connective tissue in outer medullary zones of kidneys, respectively, are as follows: for Fanconi's nephronophthisis, 0.445 and 0.197; for anti-tubular basement membrane antibody disease, 0.585 and 0.164; and for the three types of nephronophthisis-congenital hepatic fibrosis studied, 0.668 and 0.446, 1.39 and 0.921, and 1.18 and 0.12. These data support clinical impressions that the category nephrophthisis-congenital hepatic fibrosis includes more than one disease entity.     

Genetics of congenital cardiopathies

Congenital heart malformations are the most common of all birth defects, affecting 0.5-1% of all live births. Some of these malformations are due to genetic anomalies. Patterns of autosomal dominant, autosomal recessive and X-linked inheritance have been described. Mitochondrial inheritance and chromosomal anomalies can also be responsible for congenital heart malformations. Several genes for congenital heart defects have been identified. We review current knowledge on the genetic etiology of congenital heart disease.     

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??Hypertrophic cardiomyopathy??HCM?? is one of the leading causes of sudden cardiac death??SCD?? in children and young adults. The incidence of HCM in adults is 1/500??which is mainly coding sarcomere-associated protein gene mutations. The most common are MYH7 and MYBPC3. The incidence of HCM in children is unclear??and the etiology is more complicated. The clinical manifestations are highly heterogeneous. There are many kinds of non-sarcomere mutations??including metabolic storage diseases??RASopathies??neurodegenerative diseases and mitochondrial diseases. Up to now??more than 40 genes are associated with pediatric HCM. Multiple modes of inheritance account for HCM??among which autosomal dominant inheritance is the most common mode. Others include autosomal recessive??X-linked??and mitochondrial inheritance.     

Morphometric studies of cystic and tubulointerstitial kidney diseases with hepatic fibrosis in children

Portal tract fibrosis with biliary ductular enlargement or proliferation occurs in a number of genetic diseases that have cystic or tubulointerstitial renal lesions. These include some with renal cystic disease such as autosomal recessive diseases (e.g., infantile polycystic disease, juvenile polycystic disease, and Meckel's syndrome), autosomal dominant diseases (e.g., adult polycystic disease) and, rarely, tuberose sclerosis and dominant glomerulocystic disease. Portal tract fibrosis with biliary enlargement and proliferation occurs also with tubulointerstitial kidney diseases. These probably include at least three disorders in the category nephronophthisis-congenital hepatic fibrosis (one autosomal recessive disease and two either autosomal or X-linked recessive diseases) plus Jeune's syndrome (the tubulointerstitial diseases Fanconi's familial nephronophthisis and anti-tubular membrane antibody disease do not regularly cause hepatic fibrosis). Morphometric data on ratios of bile ductules to connective tissue in hepatic portal tracts show high values for infantile polycystic disease (mean, 0.616) compared to lower values for juvenile polycystic disease (mean, 0.286). That the cystic renal lesions of the first two diseases differ in type and time course is known. Similar data on ratios of glomeruli plus tubules to connective tissue in renal cortices and of tubules to connective tissue in outer medullary zones of kidneys, respectively, are as follows: for Fanconi's nephronophthisis, 0.445 and 0.197; for anti-tubular basement membrane antibody disease, 0.585 and 0.164; and for the three types of nephronophthisis-congenital hepatic fibrosis studied, 0.668 and 0.446, 1.39 and 0.921, and 1.18 and 0.12. These data support clinical impressions that the category nephrophthisis-congenital hepatic fibrosis includes more than one disease entity.     

Current perspective on the pathogenesis of central diabetes insipidus

Diabetes insipidus is a heterogeneous condition characterised by polyuria and polydipsia caused by a lack of secretion of vasopressin, its physiological suppression following excessive water intake, or kidney resistance to its action. The clinical and laboratory diagnosis is confirmed by standard tests, but recent advances in molecular biology and imaging techniques have shed new light on the pathophysiology of this disease. In many patients, central diabetes insipidus is caused by a germinoma or craniopharyngioma; Langerhans' cell histiocytosis and sarcoidosis of the central nervous system; local inflammatory, autoimmune or vascular diseases; trauma from surgery or accident; and, rarely, genetic defects in vasopressin biosynthesis inherited as autosomal dominant or X-linked recessive traits. Thirty to fifty percent of cases are considered idiopathic. Tumour-associated central diabetes insipidus is uncommon in children younger than 5 years old. Biopsy of enlarged pituitary stalk should be reserved for patients with hypothalamic-pituitary mass and progressive thickening of the pituitary stalk since spontaneous recovery may occur. Molecular biology in selected patients may identify those with apparently idiopathic diabetes insipidus carrying the vasopressin-neurophysin II gene mutation.     

Dejerine-Sottas病研究进展

Dejerine-Sottas病(Dejerine-Sottas disease,DSD)是指一种发病早的严重脱髓鞘神经病变,曾被称归类为CMT3型,但最新分类指出DSD其实是CMT1疾病谱中表型严重、伴有神经传导速度显著减慢的一类.DSD系一组遗传异质性周围神经病,遗传方式可为常染色体显性和常染色体隐性遗传,目前已经确定最常见的分子遗传学病因是PMP22、MPZ、EGR2的单等位基因突变.该病发病早,临床症状重,病情进展快,运动感觉功能均受损,神经传导速度缓慢,神经活检显示严重的脱髓鞘改变、髓鞘形成低下、多数患者髓鞘再生呈洋葱头样肥大.DSD预后不良,目前尚无明确有效的治疗策略.     

Clinical and Molecular Genetics of Inherited Hydrocephalus*

ABSTRACT Congenital hydrocephalus has a broad spectrum of etiology and has not been elucidated in terms of pathogenesis or mechanism of hydrocephalus. Recent advance of molecular genetics disclosed the genetic defects of X-linked hydrocephalus (HSAS), MASA syndrome and X-linked spastic paraplegia (SPGI), characterized by mutations in LICAM, a gene coding for a neural cell adhension molecule. Meanwhile, genetic heterogeneity in X-linked hydrocephalus has been pointed out; linkage to markers within Xq27.3. We reviewed inherited hydrocephalus and chromosomal aberrations with hydrocephalus because fibroblasts from patients with these disorders may be useful for a molecular genetic approach to inherited hydrocephalus. Animal models of congenital hydrocephalus are also very important for a comparative mapping analysis between mice and human. We have tried to clone a candidate gene of hydrocephalus using fibroblasts which show a de nove chromosomal aberration [t(4;16)(q35;q22.1)], because the synteny conservation locus for mouse hydrocephalus-3 (hy-3) gene is suggested to be located in the long arm of human chromosome 16. A rearranged band of 1.2 Mb was detected by Pulse-Field Gel Electrophoresis (PFGE) with Not I digestion using the calretinin probe. It may exist within 1.2 Mb distal apart from calretinin gene. Further analysis is carried out in order to clone this candidate gene of congenital hydrocephalus.     

The pattern of inheritance of X-linked traits is not dominant or recessive, just X-linked

Our modern concepts of genetic inheritance originated nearly a century ago. Early concepts of dominant and recessive inheritance were developed in insects and were subsequently applied to sex-linked inheritance in mammals. Years of clinical experience, however, suggest that the modern-day rules for X-linked dominant and recessive diseases do not explain why so many female carriers of X-linked 'recessive' disorders have an abnormal phenotype. In a review of 32 X-linked diseases we revealed an unexpectedly high degree of intermediate disease penetrance in females that cannot be explained by existing concepts. We recommend that the terms 'dominant' and recessive' be abandoned and that these disorders be referred to as X-linked. In this review we will present modified rules for X-linked inheritance and propose hypotheses related to the potential mechanisms that may explain differences in disease expression in females.
Conclusion : Past assumptions regarding factors that may affect phenotype in heterozygous females do not capture the extraordinarily variable expressivity of X-linked disorders in females and need to be revisited.     

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??Autosomal recessive??AR?? and X-linked recessive ??XR?? primary immunodeficiencies??PIDs?? are mainly caused by alleles with some loss-of-function??LOF??. Alleles with LOF can lead to defects of mRNA or protein expressions. The autosomal dominant??AD?? PIDs can be caused by LOF alleles??What’s more?? the AD disorders can be also due to gene mutations of gain-of-function??GOF????Most heterozygous GOF alleles can lead to enhancement of gene function or abnormal activation of expression products??resulting in related clinical symptoms. Up to 18 AD PIDs have been described with a wide range of immunological and clinical forms. Auto-inflammation and auto-immunity are found to be most common. Other clinical manifestations include infections??allergies or malignancies.     

The pattern of inheritance of X-linked traits is not dominant or recessive, just X-linked

Our modern concepts of genetic inheritance originated nearly a century ago. Early concepts of dominant and recessive inheritance were developed in insects and were subsequently applied to sex-linked inheritance in mammals. Years of clinical experience, however, suggest that the modern-day rules for X-linked dominant and recessive diseases do not explain why so many female carriers of X-linked 'recessive' disorders have an abnormal phenotype. In a review of 32 X-linked diseases we revealed an unexpectedly high degree of intermediate disease penetrance in females that cannot be explained by existing concepts. We recommend that the terms 'dominant' and recessive' be abandoned and that these disorders be referred to as X-linked. In this review we will present modified rules for X-linked inheritance and propose hypotheses related to the potential mechanisms that may explain differences in disease expression in females.Conclusion: Past assumptions regarding factors that may affect phenotype in heterozygous females do not capture the extraordinarily variable expressivity of X-linked disorders in females and need to be revisited.     

Dyskeratosis congenita: advances in the understanding of the telomerase defect and the role of stem cell transplantation

DC is a multisystem bone marrow failure syndrome exhibiting marked clinical and genetic heterogeneity. X-linked, autosomal dominant and autosomal recessive subtypes are recognized. The gene mutated in X-linked DC (DKC1) encodes a highly conserved nucleolar protein called dyskerin. Dyskerin associates with the H/ACA motif class of small nucleolar RNAs in small nucleolar ribonucleoprotein particles that are important in guiding the conversion of uracil to pseudouracil during the maturation of ribosomal RNA. Dyskerin also associates with the TERC, which is important in the maintenance of telomeres. Mutations in TERC have been identified in patients with autosomal dominant DC and in a subset of patients with aplastic anemia and myelodysplasia. Recently, heterozygous mutations in TERT have been found in some patients with autosomal dominant DC and aplastic anemia. Additionally, patients with the severe multisystem disorder, Hoyeraal-Hreidarsson syndrome, have been found to have DKC1 mutations. Collectively, these observations have demonstrated that classical DC, Hoyeraal-Hreidarsson syndrome and a subset of aplastic anemia are due to a primary defect in telomerase. The critical role of telomeres and telomerase in humans is seen in the multisystem abnormalities found in these patients, including the increased incidence of malignancy. As bone marrow failure is the principal cause of death, conventional allografts have been attempted with limited success due to the high rate of pulmonary and endothelial complications. However, outcomes have improved with the use of non-myeloablative protocols, although the follow up is too short to evaluate long term toxicity and the natural course of the disease and it may be that correction of the telomerase defect is essential for the treatment of these patients.