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PubMed1996

Blomstrand lethal osteochondrodysplasia.

We present the clinical, roentgenographic, and histologic abnormalities in a stillborn infant with Blomstrand osteochondrodysplasia. Parental consanguinity and multiplex occurrence in the patients' sibship confirm the hypothesis of autosomal recessive inheritance of this monogenic lethal entity. The unknown genetic defect interferes severely with skeletal growth through lack of chondrocyte multiplication and apparent uncoupling of the processes of enchondral ossification and skeletal growth.

Adult↗
PubMed1997

Prevalence of the factor V-Leiden mutation in four distinct American ethnic populations.

Resistance to activated protein C (APC) is the most common risk factor for venous thromboembolism, a major cause of morbidity and mortality with an incidence of about 1/1,000 per year. The Arg 506 to Gln mutation in exon 10 of the coagulation factor V gene (factor V-Leiden) has been found to be responsible for over 90% of the APC resistance cases and is an autosomal dominant trait. Initial studies have suggested that this mutation is restricted to individuals of European Caucasian extraction with an average allele frequency in European and American Caucasians of 4.4%, making it one of the most common monogenic disorders in the Caucasian population. A limited number of other ethnic populations have been tested and the mutation has been found only rarely. In our multiethnic survey of 602 individuals, Hispanic-Americans had the highest observed frequency of the factor V-Leiden mutant allele, 1.65%, while African-Americans had a somewhat lower frequency, 0.87%. No factor V-Leiden mutations were found in 191 Asian-Americans or 54 Native-Americans tested. These results indicate that the factor V-Leiden mutation segregates in populations with significant Caucasian admixture and is rare in genetically distant non-European groups. This ethnic stratification may be important in developing cost-effective selective screening programs to identify individuals at risk for thromboembolism and offer prophylactic therapy.

Alleles↗
PubMed1998

Severe craniofacial malformations and deglutition dysfunction in a brother and sister: new syndrome?

We report seemingly unique craniofacial malformations and deglutition dysfunction in a sib pair. The boy had right maxillomandibular alveolar synechae, ankylosis of right temporomandibular joint, hypoplasia of the zygomatico-maxillary region, nasal deviation to the left, choanal stenosis, and exophthalmos due to shallow orbita. His ears were apparently low-set with prominent lobules. He had severe gastroesophageal reflux and increasing respiratory problems and died at age 11 months. Psychomotor development was normal. His 10-year-old sister had similar craniofacial malformations and a cleft soft palate. She also had a severe deglutition dysfunction and developed a thoracolumbar kyphoscoliosis. Psychomotor development was normal. The parents were healthy and non-consanguineous. The malformations in the sibs do not fit any reported craniofacial malformation syndrome and may represent a previously unrecognized monogenic disorder. This may be an autosomal recessive or dominant trait with gonadal mosaicism in one of the parents.

Abnormalities, Multiple↗
PubMed2000

Genes on the X chromosome are important in undiagnosed mental retardation.

The clinical genetic diagnosis was reviewed in 429 subjects with intellectual disability in the Australian Child and Adolescent Development (ACAD) study of behavioural problems. With minor differences, the overall "general distribution by causation" was similar to that to that found by the Consensus Conference of the American College of Medical Genetics in 1995. There was a significant male excess in the whole series which was shown to reside in those with "autism," those with undiagnosed nonsyndromic mental retardation (NSMR) and those with X-linked monogenic disorders. It is argued that a substantial proportion of undiagnosed NSMR is caused by genes on the X chromosome. Some of the practical problems of assigning individuals to diagnostic groups are discussed.

Adolescent↗
PubMed1997

Phenotyping and genotyping patients with cardiovascular risk factors.

Complex diseases require precise phenotyping if their genetic basis is to be properly understood. This process is more complex than the analysis used for monogenic diseases. Collecting family phenotypic data is costly and time consuming, making such studies difficult. We have developed a family-oriented, field working approach that relies on index patients, their primary-care physicians, and a minimum number of field working staff. The index patients recruit family members by distributing packs containing the materials necessary for participation. Computer analysis of the data returned enables construction of the medical family tree. We have extended this genetic field working approach to patients with lipid disorders, arterial hypertension, non-insulin-dependent diabetes mellitus, and the 'Metabolic Syndrome'. Data from these groups can be used to identify susceptibility genes for premature arteriosclerosis. We describe a cost-effective methodology that can be used in the primary-care setting to identify 'at-risk' patients and facilitate effective targeting of limited health-care resources.

Cardiovascular Diseases↗
PubMed1999

Prevalence of congenital anomalies at birth among offspring of women at risk for a genetic disorder and with a normal second-trimester ultrasound.

The goal of this study was to determine the prevalence and the nature of congenital anomalies found at birth in offspring of women who had a normal second-trimester ultrasound and/or amniocentesis. Two groups of women were studied in our prenatal diagnosis clinic between 1991-1997. Group 1 consisted of pregnant women who had an amniocentesis for advanced maternal age (AMA), or for familial chromosomal or monogenic disorders. Group 2 consisted of pregnant women attending the prenatal diagnosis clinic and who had no indication for amniocentesis. Those with an abnormal ultrasound and/or amniocentesis were excluded. At the time of delivery, a questionnaire was sent pertaining to perinatal complications and the anomalies detected during the neonatal period. From a total of 15, 370 questionnaires sent from 1991-1997, 10,823 (group 1, n = 8,877; group 2, n = 1,946) were returned (overall response rate, 70.4%). Mean maternal age was 36 years in group 1 and 29 years in group 2. The prevalence of perinatal complications was similar in the two groups. In each group, the prevalence of all unforeseen anomalies was 2.9%. In group 1, the distribution of those anomalies was: major anomalies, 67.7%; minor anomalies, 23.9%; and multiple congenital anomalies (MCA), 8.3%. In group 2, the distribution was: major anomalies, 70.7%; minor anomalies, 24.1%; and MCA, 5.2%. In patients at risk for a genetic disease and consulting in a prenatal diagnosis clinic, the prevalence of all anomalies diagnosed at birth was 2.9%, even if the second-trimester ultrasound and amniocentesis results were normal. Therefore, it is important to inform those couples of this remaining risk.

Abnormalities, Multiple↗
PubMed2000

Familial recurrence of nonsyndromic interrupted aortic arch and truncus arteriosus with atrioventricular canal.

BACKGROUND: Multifactorial inheritance is probably involved in most cases of nonsyndromic conotruncal heart defects (CHDs), but Mendelian transmission is often suspected. RESULTS: We report on a family with recurrence of nonsyndromic CTHD in two double first cousins; i.e., two brothers married two sisters. One of the cousins (case 1) had interrupted aortic arch (IAA) type B, while the other one (case 2) had truncus arteriosus (TA) with atrioventricular canal defect (AVCD). CONCLUSIONS: Our family further supports monogenic inheritance of CTHDs. In addition, the presence of TA associated with AVCD in one of the patients confirms the higher occurrence of CTHD in families with complex TA. The absence of 22q11 microdeletion (del22q11) in our patients, as in several literature reports of familial CTHDs, supports the existence of genes different to those located on chromosome 22q11 which could be implicated in the pathogenesis of CTHDs.

Aorta, Thoracic↗
PubMed1998

Molecular genetics of the long QT syndrome: two novel mutations of the KVLQT1 gene and phenotypic expression of the mutant gene in a large kindred.

At least three different gene loci were recently shown to account for the long QT syndrome (LQTS), a monogenic disorder with altered myocardial repolarization and occurrence of life-threatening cardiac arrhythmias. We screened 44 unrelated probands for mutations of the gene encoding the cardiac potassium channel KVLQT1 using single-strand conformational polymorphism (SSCP) and subsequent DNA sequencing. Two different mutations, T182I and D188N, were identified in two separate pedigrees. Cosegregation of the mutation with the disease phenotype was evident in both families. No mutations were identified at codon 212, previously suggested to represent a mutational hot spot of the KVLQT1 channel, in any of the 44 probands. The large pedigree with the D188N mutation (30 affected and 43 nonaffected individuals) permitted an analysis of expression of the mutant gene in its documented carriers. Although the mean (+/-SD) QTc interval was markedly longer in affected (484+/-38 ms) than in nonaffected individuals (406+/-27 ms, P < 0.001), there was a marked overlapping of individual values in these two groups. QTc values in symptomatic and asymptomatic carriers of the mutant gene were not significantly different. In conclusion, we have identified two novel mutations of the KVLQT1 component of a cardiac potassium channel. Our data support the functional significance of the pore-S6 domain of this membrane protein and emphasize the diagnostic usefulness of DNA analyses in families with LQTS.

DNA Mutational Analysis↗
PubMed2000

The Human Genome Project--an overview.

The human genome sequence will underpin human biology and medicine in the next century, providing a single, essential reference to all genetic information. The international program to determine the complete DNA sequence (3,000 million bases) is well underway. As of January 2000, 50% of the sequence is available in the public domain. A comprehensive working draft is expected this year, and the entire sequence is projected to be finished in 2003. DNA sequencing is carried out on mapped, overlapping bacterial clones of 150-200 kb. The working draft comprises assembled unfinished sequence and is released immediately in the public domain. The draft sequence of each clone is then completed, by closing any remaining gaps and resolving any ambiguities, before the entire sequence is checked, annotated, and submitted to the public databases. The sequence of each clone is finished to an accuracy of >99.99%. The availability of a reference sequence of the genome provides the basis for studying the nature of sequence variation, particularly single nucleotide polymorphisms (SNPs), in human populations. SNP typing is a powerful tool for genetic analysis, and will enable us to uncover the association of loci at specific sites in the genome with many disease traits. SNPs occur at a frequency of approximately 1 SNP/kb throughout the genome when the sequence of any two individuals is compared. Programs to detect and map SNPs in the human genome are underway with the aim of establishing a SNP map of the genome during the next two years. The human genome sequence will provide a complete description of all the genes. Annotation of the sequence with the gene structures is achieved by a combination of computational analysis (predictive and homology-based) and experimental confirmation by cDNA sequencing. Detecting homologies between newly defined gene products and proteins of known function helps to postulate biochemical functions for them, which can then be tested. Establishing the association of specific genes with disease phenotypes by mutation screening, particularly for monogenic disorders, provides further assistance in defining the functions of some gene products, as well as helping to establish the cause of the disease. As our knowledge of gene sequences and sequence variation in populations increases, we will pinpoint more and more of the genes and proteins that are important in common, complex diseases. A more detailed understanding of the function of the human genome will be achieved as we identify sequences that control gene expression. Given the availability of gene sequences, the expression status of genes in particular tissues can be monitored in parallel. By comparing corresponding genomic sequences in different species (for example: man, mouse, chicken, and zebrafish), regions that have been highly conserved during evolution can be identified, many of which reflect conserved functions such as gene regulation. These approaches promise to greatly accelerate our interpretation of the human genome sequence.

Human Genome Project↗
PubMed1996

Influence of apolipoprotein E genotypes on plasma lipid and lipoprotein concentrations: results from a segregation analysis in pedigrees with molecularly defined familial hypercholesterolemia.

Familial hypercholesterolemia (FH) is a monogenic disorder caused by mutations in the low-density lipoprotein (LDL) receptor gene. Large variations in plasma lipids and lipoprotein levels have been observed in FH families. These may be caused by other environmental and genetic factors of which apolipoprotein E (apo E) is a candidate. The possible influence of apo E polymorphism on components of variation in plasma LDL-C, triglycerides, high-density lipoprotein cholesterol (HDL-C), and lipoprotein(a) (Lp(a)) levels was investigated in 235 members of 14 families with FH. Sex-and age-adjusted mean LDL-C was influenced significantly by the apo E genotype in non-FH subjects (P <or= .01), and a similar trend was observed in FH cases. Mean plasma levels of triglyceride, HDL-C, and Lp(a) were not significantly different across the apo E genotypes in FH and in non-FH family members. Complex segregation analysis was first applied to these sex- and age-adjusted data. In addition to the major gene involved in LDL-C levels (i.e., the LDL receptor gene), there was evidence for a non-transmitted environmental major factor in addition to polygenic effect that explained the mixture of distributions in TG and a major effect in addition to polygenic loci which influenced Lp(a) levels. There was no evidence for a single major factor controlling HDL-C levels in these pedigrees. When the segregation models allowed apo E regression coefficients to be ousiotype (class) specific, the results suggested that apo E genotypes have a significant effect on LDL-C, TG, and Lp(a) levels. In conclusion, the analysis presented here supports the concept that the apo E gene has an important role in the regulation of plasma lipid and lipoproteins in FH.

Adolescent↗
PubMed2000

Clinico-pathological characteristics of BRCA1- and BRCA2-related breast cancer.

Approximately 2% to 5% of all breast cancers are hereditary, meaning that the cancer predisposition is carried as a monogenic trait. Several highly penetrant breast cancer predisposing genes have been identified. These discoveries will permit a refined description of breast cancer occurring as part of the different genetic syndromes. We reviewed the medical literature on the clinico-pathological features of breast cancer associated with the major breast cancer susceptibility genes BRCA1 and BRCA2. BRCA1-associated breast cancers are more frequently ductal invasive, high-grade carcinomas with an important lymphocytic infiltration. They are aneuploid, estrogen and progesterone receptors negative, and p53 positive. BRCA2-related breast cancers tend to be higher-grade tumors than are non-hereditary cases, although this association is less strong then for BRCA1 cases. These tumors exhibit substantially less tubule formation, but mitotic count and cellular pleomorphism do not differ significantly from those of sporadic cases. The overall pattern of the identified pathological characteristics suggests a carcinogenic pathway in BRCA1- and BRCA2-related breast cancers different from that found in sporadic cases. The probability of finding a BRCA1/2 germ-line mutation is partly determined by these characteristics. In addition, these features will likely influence the behavior of BRCA1/2-related breast cancer.

Aneuploidy↗
PubMedDate not supplied

Risk of recurrence of craniospinal anomalies.

The authors analyzed 1,655 situations from their Genetic Counseling Service over a 15 year period where the reason for counseling was craniospinal anomaly (neural tube defects and/or hydrocephalus) in the family. Excluding the obviously monogenically inherited cases, they investigated pregnancies undertaken after 1,285 isolated and 177 multiple forms of craniospinal abnormalities. The recurrence rate of craniospinal defects was found to be 3.66%, which is about ten times higher than the general population risk, supporting the theory of the multifactorial threshold model in the inheritance of these anomalies. The recurrence risks of neural tube defects and of hydrocephalus were 3.47% and 2.95%, respectively. The authors concluded that recurrence risk is mainly influenced by the pathoanatomic severity of the involved anomaly, the degree of relationship, and the number of affected relatives in the family. There is a positive correlation between the pathoanatomic severity of the anomaly in the proband and the offspring. At least in one-half of the cases the same type of anomaly was observed again in the offspring as in the proband. Attention is drawn to the fact that hydrocephalus (ventriculomegaly) is often manifested only in the second half of gestation. Therefore, performing ultrasound examination is strongly recommended not only at the 18th but at the 24th week of gestation, as well in pregnancies with a positive history of neural tube defects and/or hydrocephalus.

Family Health↗
PubMed2000

Calculation of recurrence risks for heterogeneous genetic disorders.

We present general formulae for several common situations in the genetic counseling of heterogeneous disorders. The occurrence or not of parental consanguinity is taken into account, since it distorts significantly the prior probabilities favoring the different mechanisms. Nonsyndromic deafness is used as a numerical application, since it can be produced by any type of monogenic inheritance and can be mixed with variable proportions of environmental cases. Recurrence risks are calculated including or not including environmental factors in the origin of the defect. In underdeveloped countries the proportion of environmentally determined cases of deafness is significantly higher than in first-world countries. Therefore, when environmental causes cannot be excluded, recurrence risks are always higher in developed than in developing countries. On average, when parental consanguinity is present there is a significant increase in recurrence risks for deafness, whether environmental factors are included or not.

Consanguinity↗
PubMed2001

Possible relationship between the van der Woude syndrome (vWS) locus and nonsyndromic cleft lip with or without cleft palate (NSCL/P).

Cleft lip with or without cleft palate (CL/P) is one of the most common congenital malformations in humans occurring with a birth prevalence of approximately 1:1,000. CL/P may be part of a defined syndrome, sequence or association, although most individual or familial cases present as an isolated (nonsyndromic) malformation (NSCL/P). Inheritance is generally regarded as multigenic although, in some families, NSCL/P seemingly segregates as a monogenic trait. On the other hand, van der Woude syndrome (vWS) is a rare autosomal dominant with cardinal features of lower-lip pits (LLP) and CL/P or cleft palate (alone). Since none of these traits is present in all mutation carriers, some individual or familial vWS cases, especially those lacking LLP, are indiscernible from NSCL/P, raising the question whether allelic variation at the vWS locus could underlie NSCL/P. This question was addressed using parametric linkage (LOD score) analysis in 21 multiplex NSCL/P families based on a tightly linked microsatellite marker (D1S3753), and nonparametric analysis using the transmission/disequilibrium test (GTDT) in 106 NSCL/P triads and selecting markers D1S205, D1S491, and D1S3753. No evidence for linkage of NSCL/P to vWS was found on the 21 families using the LOD score approach. In contrast, TDT yielded a significant P value of 0.04 for D1S205, supporting involvement of vWS in NSCL/P in a complex, modifying/polygenic manner rather than as a monogenic/major disease locus.

Alleles↗
PubMed2000

Embryo implantation after biopsy of one or two cells from cleavage-stage embryos with a view to preimplantation genetic diagnosis.

Preimplantation genetic diagnosis (PGD) can be offered as an alternative to prenatal diagnosis (PND) to couples at risk of having a child with a genetic disease. The affected embryos are detected before implantation by fluorescent in situ hybridisation (FISH) for sexing (X-linked diseases) and chromosomal disorders (numerical and structural) or by polymerase chain reaction (PCR) for monogenic disorders (including some X-linked diseases). The accuracy and reliability of the diagnosis is increased by analysing two blastomeres of the embryo. However, the removal of two blastomeres might have an effect on the implantation capacity of the embryo. We have evaluated the implantation of embryos after the removal of one, two or three cells in 188 PGD cycles where a transfer was done. The patients were divided into five groups: a first group which received only embryos from which one cell had been removed, a second group which received only embryos from which two cells had been removed, a third group which received a mixture of embryos from which one and two cells had been taken, a fourth group where two and three cells had been removed, and a fifth group where three cells had been removed. The overall ongoing pregnancy rate per transfer was 26.1%, the overall implantation rate per transfer was 15.2% and the overall birth rate was 14.2%. Although pregnancy rates between the groups cannot be compared because the second group (two cells removed) contains more rapidly developing and therefore 'better quality' embryos, an ongoing pregnancy rate of 29.1% and an implantation rate of 18.6% per transferred embryo in this group is acceptable, and we therefore advise analysing two cells from a > or =7-cell stage embryo in order to render the diagnosis more accurate and reliable.

Biopsy↗
PubMed2000

Screening of the PKD1 duplicated region reveals multiple single nucleotide polymorphisms and a de novo mutation in Hellenic polycystic kidney disease families.

Mutations in the PKD1 gene account for approximately 85% of cases with autosomal dominant polycystic kidney disease (ADPKD1; MIM# 601313), which is considered one of the most frequent monogenic disorders, with a frequency of approximately 1:1000. The main symptom is the formation of fluid-filled cysts in the kidneys and less often in other organs, such as the liver and pancreas. Since the cloning of the gene many mutations have been identified, although the screening is hampered by several unique features of this gene, the most significant one being that approximately 70% of the sequence at the 5'-end, is reiterated elsewhere on chromosome 16 with homology approaching 95%. Here, we used an oligonucleotide primer anchored in the unique part in exon 34, paired with a forward primer in exon 23 for specifically amplifying PKD1 sequences. We screened for mutations in samples from 32 Hellenic ADPKD families. We detected seven sequence variants, five of which most probably are single nucleotide polymorphisms (SNPs), especially useful for linkage analysis and disease association studies. One is a missense change, segregating with ADPKD in one family. The last one is a missense non-conservative change, H2921P, which appeared de novo in the proband, concurrently with the disease phenotype, and was passed on to another two generations. Two siblings who inherited the same haplotype as the proband, but not the de novo mutation, were not affected. This is only the fourth case of a molecularly documented de novo mutation in ADPKD. Somatic mosaicism in peripheral blood leukocytes of the proband was tested and excluded. Hum Mutat 16:176, 2000.

Aged↗
PubMed2000

Proposed mechanism for a novel insertion/deletion frameshift mutation (I414G415ATCG-->CCA) in the hepatocyte nuclear factor 1 alpha (HNF-1 alpha) gene which causes maturity-onset diabetes of the young (MODY).

Maturity-onset diabetes of the young (MODY) is a monogenic subgroup of non-insulin dependent diabetes (NIDDM) characterized by an early age of diagnosis (usually < 25 years) and an autosomal dominant mode of inheritance. Mutations in the hepatocyte nuclear factor 1 alpha (HNF-1alpha) [MODY3] gene represent the most common cause of MODY in the UK and a common cause of MODY in many other populations. Sixty-three different mutations have been described in a total of 112 families worldwide. This report describes two families, not known to be related, who carry a novel insertion/deletion mutation (I414G415ATCG-->CCA) and a 6bp intronic deletion of the HNF-1alpha gene in cis. We propose that the insertion/deletion mutation has arisen by formation of a hairpin loop due to the presence of a quasi-palindromic sequence, followed by insertion of CC and deletion of TCG resulting in the increased stability of the hairpin loop.

Adult↗
PubMed2000

Hepatocyte nuclear factor 1 alpha (HNF-1 alpha) mutations in maturity-onset diabetes of the young.

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, early age of onset (<25 years) and pancreatic beta-cell dysfunction. MODY is genetically heterogeneous with five different genes identified to date: hepatocyte nuclear factor-4 alpha (HNF-4 alpha) [MODY1]; glucokinase [MODY2]; hepatocyte nuclear factor-1 alpha (HNF-1 alpha) [MODY3]; insulin promoter factor-1 (IPF-1) [MODY4]; and hepatocyte nuclear factor-1 beta (HNF-1 beta) [MODY5]. Mutations in the HNF-1 alpha gene represent a common cause of MODY in the majority of populations studied. Sixty-five different mutations have been described in a total of 116 families. The most common mutation is a C-insertion (P291fsinsC) in the polyC tract of exon 4, which has been reported in 22 families. The identification of an HNF-1 alpha gene mutation in a patient with type 2 diabetes confirms the diagnosis of MODY and has important implications for clinical management.

Adult↗