Molecular biology in genetic counseling of Duchenne and Becker myopathy]

From 1985-1991, molecular biology studies were carried out in 115 families affected with X-linked muscular dystrophy (DMD/BMD), including 59 prenatal diagnoses. The approach has changed over the last 6 years when new intragenic markers and cDNA probes became available. The polymerase chain reaction technique allows a rapid detection of dystrophin deletions, but classical Southern blot technique remains useful for restriction length polymorphism analysis. Fifty percent (42/85) of patients with DMD/BMD exhibited deletions of the dystrophin gene. In affected families with a detectable deletion, carrier detection is possible by gene dosage analysis and prenatal diagnosis is reliable. When no deletion is found, carrier detection and prenatal diagnosis depends on linkage analysis using polymorphic probes. Due to the high recombination rate, several markers need to be used. The information provided by linkage analysis must be interpreted given the proper family structure.     

Restriction Fragment Length Polymorphism Analysis in Healthy Japanese Individuals and Japanese Families with Gaucher Disease

We analysed the restriction fragment length polymorphism (RFLP) of 30 unrelated, healthy Japanese individuals and the members of seven Japanese families with Caucher disease (5 Type I, 2 Type III) with the cDNA for human glucocerebrosidase, to investigate the frequency of the RFLP among healthy Japanese individuals and to determine the feasibility of the use of this probe DNA for carrier detection and prenatal diagnosis in Japanese families with Caucher disease. In the Pvu II polymorphism, the common allele reported by Sorge et al [1] was the rare allele for healthy Japanese individuals. The frequency of the common allele (+) in Japanese was 0.75 and the rare allele (-) was 0.25. The RFLP study was informative for carrier detection in the family in which both parents were heterozygous for the Pvu II polymorphism. Even in the family in which only one parent was heterozygous, carrier detection was feasible by combining the clinical history and the RFLP, although prenatal diagnosis was not feasible. The Kpn I polymorphism was not detected. It is necessary for precise carrier detection and prenatal diagnosis to investigate other restriction endonucleases which reveal the RFLP. ( Acta Paediatr Jpn 1989; 158 - 162)     

Carrier Diagnosis of Duchenne Muscular Dystrophy Using Fluorescent CA Repeat Polymorphism

The diagnostic efficacy was compared between the fluorescent CA repeat polymorphism analysis and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis for carrier diagnosis of Duchenne muscular dystrophy. Nine females from seven pedigrees were examined. Polymorphic alleles were examined by the fluorescent labelling method in eight loci within the dystrophin gene. PCR-RFLP analysis was performed in a total of six loci within the dystrophin gene. Carrier diagnosis could not be made in three females of two pedigrees due to an inability to detect polymorphic alleles by PCR-RFLP. In contrast, CA repeat polymorphism analysis allowed successful carrier diagnosis in nine subjects. These findings suggest that the fluorescent CA repeat polymorphism analysis provides a simple, safe and effective alternative to PCR-RFLP analysis for carrier diagnosis of Duchenne muscular dystrophy.     

Improved definition of carrier status in X-linked hypohidrotic ectodermal dysplasia by use of restriction fragment length polymorphism-based linkage analysis

The detection of carriers of the X-linked disorder hypohidrotic ectodermal dysplasia is problematic because of random X-inactivation; the diagnosis was previously based on the observation of subtle defects in ectodermal structures in at-risk females. Linkage studies have recently mapped hypohidrotic ectodermal dysplasia to the region Xq11-q21.1. We assessed the improvement in carrier detection by the method of linkage analysis, in which restriction fragment length polymorphisms were used as markers, in 72 at-risk female members of 29 families. Carriers analyses were based on pedigree information, dental examination of at-risk females (phenotype), and DNA analyses at seven linked marker loci. Linkage analysis based on restriction fragment length polymorphisms significantly improved risk estimates over those based on phenotype and pedigree alone. When all available information was combined, 85% (61/72) of the at-risk females had final risks of less than 5% or greater than 95%, and 68% (49/72) had risks less than 1% or greater than 99%. A diagnosis of hypohidrotic ectodermal dysplasia was also excluded (97.5% probability) by DNA and linkage analyses from a sample of cord blood from an at-risk male; a similar approach can be taken for prenatal diagnosis of the disorder.     

Hypoxanthine-guanine phosphoribosyltransferase gene analysis for Japanese patients with Lesch-Nyhan syndrome

The Lesch-Nyhan syndrome results as a consequence of a severe deficiency of functional activity of purine salvage enzyme, hypoxanthine phosphoribosyltransferase (HPRT). We performed Southern blot analysis for five patients and their families using full length cDNA of the HPRT gene as a probe. Pst I digested Southern blot analysis revealed a large deletion that included exon 2 in patient 3. The size of this deletion was about 4.4 Kb. The mother of this patient had the same mutated allele and a normal one (heterozygote). This type of mutation from a Lesch-Nyhan syndrome patient has not been previously reported. The restriction fragment length polymorphism (RFLP) pattern was analyzed by Bam HI digested Southern blot analysis for one family who had no major gene abnormality. We determined from this analysis that the sister of the patient was a Lesch-Nyhan syndrome carrier and the fetus (brother) was normal for HPRT activity. This study shows RFLP analysis is still useful for carrier detection and prenatal diagnosis of Lesch-Nyhan syndrome.     

良性家族性婴儿惊厥一家系基因定位及钾离子通道基因测序研究

目的：对一良性家族性婴儿惊厥家系进行基因定位，并对候选基因钾离子通道基因KCNQ2进行测序分析。方法：共抽取14例血样，包括全部9例患者。同时对家系全部成员行脑电图、全身及神经系统检查。在19qD19S245至D19S250间选择6对微卫星标记进行连锁分析。KCNQ2基因外显子测序引物序列采用Biervert等所报道的序列。结果：该家系两点间连锁结果排除了与19q及8q24连锁的可能。在20q13.3(D20S480)最大LOD值为0.60（外显率90%）。染色体单体型分析提示可能与20q13.3连锁。KCNQ2基因测序发现外显子6有一C/T杂合突变多态性，外显子17有1个A/C错义多态性，内含子14人一4个碱基插入多态性。结论：该家系的连锁结果排除了与19q的连锁可能，提示BFIC的遗传多态性。该家系所发现的多态性变化对其他癫痫家系的连锁分析及其他癫综合征分子遗传学机制的研究，均有重要意义。     

Italian experience regarding the prevention of Duchenne and Becker muscular dystrophies

The indirect approach to carrier detection and prenatal diagnosis of Duchenne and Becker muscular dystrophies based on the study of DNA polymorphisms closely linked to this gene has been followed by five Italian laboratories in the study of 106 pedigrees. Out of 354 women studied up to 1 May 1987, 147 were identified as carriers because of pedigree information and/or of increased creatine phosphokinase (CPK) values. Of the remaining 207, 184 could be assigned to three arbitrarily defined risk categories (low, intermediate and high) using linkage analysis. This disaggregation of women at risk is clearly more useful than that defined before DNA analysis, in which the same 184 women could be assigned only to the low or intermediate risk categories. Prenatal diagnosis was theoretically possible in 90% of carrier women, and was actually performed in 14 pregnancies, which led to the identification of four affected male foetuses, one also having Down syndrome.Abbreviations DMD Duchenne muscular dystrophy - BMD Becker muscular dystrophy - CPK creatine phosphokinase - PND prenatal diagnosis     

Early diagnosis in X-linked agammaglobulinaemia

The genetic transmission of X-linked agammaglobulinaemia (XLA) can be determined with high probability using closely linked DNA restriction fragment length polymorphisms (RFLP's). In a family known to be at risk for XLA in male offspring, RFLP analysis demonstrated that the mother was an XLA carrier and her newborn son was affected. The infant developed immunological deficiencies a few months later, confirming the diagnosis. RFLP analysis provides a method for carrier detection, prenatal diagnosis and presymptomatic diagnosis of XLA, which plays a significant role in prevention of the disease.Abbreviations XLA X-linked agammaglobulinaemia - RFLP restriction fragment length polymorphism - PBMC peripheral blood mononuclear cells - Ig Immunoglobulin - PWM pokeweed mitogen - SAC Staphylococcus aureus cowan A strain     

脊髓性肌萎缩的基因诊断和产前基因诊断研究

目的探讨中国人脊髓性肌萎缩(SMA)基因诊断和产前基因诊断的可行性。方法应用复合聚合酶链反应-限制性片段长度多态(PCR-RFLP)方法对31例SMA患儿进行神经元存活基因(SMN)第7外显子缺失分析,并对2例有SMA阳性家族史的家系进行了产前基因诊断。结果96.8％(30／31)SMA患儿携有SMN基因第7外显子缺失。2例产前基因诊断的病例均无SMN基因第7外显子缺失。结论SMN基因缺失检测技术可用于SMA患儿的基因诊断和产前基因诊断。     

DNA analysis of ornithine transcarbamylase deficiency

By analysing the restriction fragment length polymorphism (RFLP) detected by an ornithinetranscarbamylase (OTC) gene specific DNA probe, we followed the segregation of the defective gene in two families with OTC deficiency (X-linked disease). We were able to exclude some female family members as carriers. In one case a doubtful result obtained in a biochemical carrier detection test (by examining the renal orotic acid excretion after a protein load) could be clarified by DNA analysis. In every family with OTC deficiency, carrier detection should be biochemical with additional DNA analysis. Previous results of the biochemical carrier test should be controlled by DNA analysis, especially when normal results were obtained.Abbreviations OTC ornithinetranscarbamylase - RFLP restriction fragment length polymorphism - DNA desoxyribonucleic acid - cDNA complementary DNA     

Prenatal diagnosis and carrier detection of inherited immunodeficiency disorders

Clinical immunodeficiency states may arise as a consequence of genetic defects in the immune system. An increasing number of such diseases are now being identified and in some cases the underlying defects are well understood. In some disorders the outlook has been improved by advances in available treatment, but in most the prognosis is still very poor with death in early infancy in many cases. Recently, there have been significant advances in techniques for prenatal diagnosis and carrier detection for some of these disorders. These include the use of gene tracking by restriction fragment length polymorphism (RFLP) and deletion analysis, detection of defective gene products, assessment of cellular dysfunction, cell series analysis, and X-chromosome inactivation studies for carrier detection.     

Family studies in ornithine transcarbamylase deficiency.

Six families with at least one infant each with confirmed ornithine transcarbamylase deficiency were investigated by DNA analysis. All the affected sons had died, and no DNA had been stored. Using the restriction endonucleases MspI and Bam HI three restriction fragment length polymorphisms were detected which led to eight distinct haplotypes. Using these results and those of protein loading tests that diagnosed heterozygote (carrier) status in some family members, some carriers were detected, and prenatal diagnosis was offered to two families. In two further families no polymorphisms were found and no prenatal diagnosis was possible. In the remaining two families prenatal diagnosis was impossible because of the lack of DNA from an affected or unaffected son, or in one case from the father, of an obligate carrier. These studies emphasise the importance of preserving tissue for DNA extraction from infants dying of inborn errors of metabolism, and also show the way in which information from conventional biochemical studies can complement diagnostic tests using DNA.     

Familial neurofibromatosis type 1: clinical experience with DNA testing.

To determine how DNA testing for familial neurofibromatosis type 1 (NF-1) would be used in a clinical setting by patients and physicians, we performed confirmatory DNA testing on 24 individuals with a family history of NF-1 and on nine couples who requested DNA testing for current or future prenatal diagnosis. A further eight families were unsuitable for DNA linkage testing because of their pedigree structure. For the majority of persons the certainty of the test result was 95% to 99%. In five individuals, only one of whom was less than 6 years of age, the DNA-based diagnosis was discrepant with the clinical diagnosis at the time of referral. In all five cases, results of subsequent clinical re-examinations were consistent with the DNA diagnosis. We conclude that DNA testing by linkage analysis may be most useful as an adjunct to the clinical diagnosis of familial NF-1 (1) in children less than 6 years of age in whom the full manifestations may not yet be apparent, (2) in NF-1 families interested in prenatal testing, and (3) when the resources available for a complete clinical examination are limited.     

全面性癫癎伴高热惊厥附加症基因定位及GABRA6基因测序研究

目的　对全面癫伴高热惊厥附加症 (GEFS )家系进行基因定位 ,并对候选基因进行测序研究。方法　用连锁分析的方法对GEFS 家系进行研究 ;设计GABRA6外显子 内含子交界处全部 9对内含子引物 ,采用Sanger双脱氧链终止法 ,对GABRA6PCR测序。 结果　在 5 q34区域最大LOD值 3.815。GABRA6基因测序显示外显子 8有一C/G多态性。结论　GEFS 症致病基因在 5 q34区域取得了肯定的连锁关系。在该研究的两家系未发现GABRA6基因突变 ;所显示的单个碱基多态性对其他癫家系的连锁分析及其他癫综合征分子遗传学机制的研究均有意义     

Carrier prediction of cystic fibrosis in 36 families by means of restriction fragment length polymorphism

Transmission of cystic fibrosis (CF) was studied in 36 families with at least one affected and one unaffected child. DNA was prepared from peripheral leukocytes and submitted to restriction fragment length polymorphism (RFLP) analysis with two CF probes (pj3.11 and met). Twenty families were shown to be informative so that accurate predictions could be made of the status of the offspring. Sixteen were only partially informative. The allele frequency was similar to that originally reported except for one MspI site detected with the pj3.11 probe, for which we found a significantly higher heterozygote frequency, making it more informative than expected in our population sample. Pedigree analysis demonstrated no obligate recombinant between CF and the polymorphic markers.Abbreviations CF cystic fibrosis - RFLP restriction fragment length polymorphism     

云南苯丙氨酸羟化酶基因内(TCTA)n多态性及其在苯丙酮尿症诊断中的应用

目的应用苯丙氨酸羟化酶（ＰＡＨ）基因内（ＴＣＴＡ）ｎ多态性连锁分析进行经典型苯丙酮尿症（ＰＫＵ）的基因诊断和产前诊断。方法应用聚合酶链反应扩增片段长度多态性（ＰＣＲＡｍｐＦＬＰ）方法,分析云南省１３个家系苯丙氨酸羟化酶（ＰＡＨ）基因内（ＴＣＴＡ）ｎ多态性。结果在１３个家系中检测到２２４～２５２ｂｐ的８种等位片段,其ＰＩＣ为０．６９８,杂合频率是５１％。可诊断率为１００％和５０％的家系各６个,１个家系因双亲带型为纯合型而未能诊断,可诊断率为６９％。完成１例产前基因诊断和２例回顾性的基因诊断。结论（ＴＣＴＡ）ｎ的ＰＣＲＡｍｐＦＬＰ分析可作为经典型ＰＫＵ基因诊断和产前诊断的一种简便有效的方法。     

Value of Dna Analysis with Multiple Dna Probes for the Detection of Hemophilia a Carriers

Detection of hemophilia carriers is an important issue and should be addressed with great care. The allelic frequencies of three intragenic probes (Bcl I for probe p1 14.12, Xba I for probe p482.6, and Bgl I for probe C) and ow linked probe (Bgl II for probe DX 13) are reported, together with their diagnostic yield singly and in combination. In this series, 725 individuals (405 females) an 156 families were analyzed for restriction fragment-length polymorphisms. A total of 255 females (63%) were found to be information for their carrier state with one or more probes. The most informative intragenic probe was p482.6 (useful in 49% of informative females). The most informative probe was DX 13 (useful in 59% of informative females), but this k a linked probe that carries a 5% risk of cross-over. By the use of probes p1 14.12, p482.6, and DX 13, almost 98% of all the informative females could be detected. In about 71% of families with a family history and a known carrier, prenatal diagnosis was feasible.     

Prenatal Diagnosis of Oculocutaneous Albinism Type I: Review and Personal Experience

Oculocutaneous albinism type I (OCA I) comprises autosomal recessive syndromes of hypopigmentation and low vision, caused by the lack of tyrosinase activity. Affected families seek genetic counseling and prenatal diagnosis as preventive measures. Until recently, prenatal diagnosis of OCA I was achieved by histologic and electron microscopic examination of fetal skin biopsies. Lately, a molecular genetic approach has become possible by the identification of the two mutated copies of the TYR gene, coding the tyrosinase, in which over 60 mutations have been identified. We report here our experience in prenatal diagnosis of OCA I using the two strategies. Thirty-four prenatal tests were performed in fetuses at risk for OCA I. In 31 cases the diagnosis was made in fetal scalp biopsies using the histological approach. The microscopic observations revealed normal melanogenesis in 26 biopsies. Five albino fetuses were diagnosed by the demonstration of arrest of melanogenesis in early stages I and II. In three pregnancies, molecular genetic tests were performed on DNA extracted from amniocytes, using direct mutation analysis (in one), and complemented by linkage analysis (in two). One albino and two normally pigmented fetuses were diagnosed. The prenatal molecular genetic test can be applied to families when at least one mutation is diagnosed in the albino patient. The histological approach is applicable in all families at risk for OCA I.     

Within-gene interaction between c.135 G/A genotypes and RET proto-oncogene germline mutations in HSCR families.

Hirschsprung disease (HSCR) is considered a model for a complex inheritance disorder. Several genes, including the major HSCR-susceptibility RET proto-oncogene, play an aetiological role in the development of HSCR. Genetic linkage analysis in familial HSCR with both long- and short-segment phenotypes has demonstrated a tight linkage to the RET locus, while the phenotype within a HSCR family is characterised by an incomplete penetrance or a variable extension of the aganglionosis. Therefore, additional genetic alterations of RET are postulated in the aetiology or modification of the HSCR phenotype. In this study, the coding region of all 21 exons of the RET proto-oncogene, including the flanking intronic sequences, were investigated by direct DNA sequencing in a HSCR population. We genotyped the c.135 G/A polymorphism and resolved haplotypes comprising the mutation locus and the c.135 G/A polymorphism. Twenty different mutations were detected in 18 of 76 HSCR patients. In ten families the mutations were inherited from the parents, while only four patients had a positive family history for the disease. Moreover, in all ten families an incomplete penetrance of the HSCR phenotype was observed. We have investigated the effect of the non-mutated wild-type allele as well as the c.135 G/A polymorphism on the phenotype within the HSCR families. Our findings support the notion that both RET alleles are involved in the pathogenesis of a subgroup of HSCR patients in a dose-dependent fashion. Additionally, we have shown a modifying effect of the c.135 G/A polymorphism on the HSCR phenotype within HSCR families.