ESHG Plenary Sessions

The International Human Genome Sequencing Consortium has not curtailed its efforts with the annoucement of the completion of the draft sequence (June 2000). On the contrary significant progress has been accomplished since the analysis (February 2001) and the hope for a complete sequence for 2003 is still realistic.
The draft sequence has been improved by doubling the number of shotgun reads of the BAC clones included in the assembly (about 30,000 clones). This resulted in larger assembled contigs which could be more frequently ordered and oriented. Finishing is the major focus at present.
To date chromosomes 14, 20, 21, 22 and Y are fully sequenced. The published draft sequence (assembled September 2000) contained some 220,000 sequence gaps among which about 2000 were not bridged by cloned DNA fragments. The sequence gap number has decreased to 98,000 (assembled August 2001) and the number of clone gaps has been reduced to 390 (November 2001). Similarly the global coverage has increased from 2,700 Mb (September 2000) to 2,900 Mb (August 2001). 2,048 Mb of non-redundant sequence (64%) is in the finished state.
Because of the high redundance of the number of BAC clones that were used for the draft sequence, a large number of sequence variants could be identified and more than 4,000,000 SNPs are presently featured in dbSNP. Sequence analysis does not reveal similar spectacular changes. The gene count remains controversial. However the number of 25,000 confirmed genes is not going to increase rapidly since it is dependent on experimental validations.

A. Fischer;
Unité d’Immunologie et d’Hématologie Pédiatriques and INSERM U 429 - University Hospital Necker-Enfants Malades, Paris, FRANCE.

Gene therapy is an attractive option for a number of genetic disorders. Genetic supplementation could in theory lead to long lasting disease phenotype correction. However, efficient targeting, induction of long lasting transgene expression and a few other issues limit present application. Given the status of gene transfer technology, two settings appear more favourable. The first relies on a growth advantage conferred to transduced cells by transgene expression combined with cell longevity. This is best examplified by the severe combined immunodeficiency (SCID) condition. X-linked (SCID) is caused by mutations of the gene encoding the gc receptor subunit. Induction of expression on lymphocyte progenitors by retroviral mediated gene transfer leads to tremendous cell proliferation resulting in the generation of a high number of mature, long lived T lymphocytes. Based on this strategy, seven out of 8 patients with typical XL-SCID have benefited from gene therapy. They have indeed recovered a functional immune system with a follow-up up to 3 years without adverse effects. A dozen of other genetic conditions might therefore also benefited form this approach. The second favourable setting is based on continuous secretion of a protein in blood stream by transduced cells of various sources such as hepatocytes, fibroblaste or muscular cells. AAV vectors appear well-suited. As based on preliminary results, application to the treatment of inherited hemostasis disorders (hemophilia) or lysosomal storage disorders can be considered. Broader application of gene therapy is awaiting progress in gene transfer technology. The advent of lentiviral vectors, enabling transduction of non cycling cells, if proven safe, might provide a significant boost to gene therapy.

A. J. Jeffreys, K. Holloway, L. Kauppi, C. May, R. Neumann, T. Slingsby, T. Taylor;
University of Leicester, Leicester, UNITED KINGDOM.

To analyse the fine-scale distribution of meiotic recombination events in human chromosomes, we have developed PCR methods to detect crossovers in sperm DNA. Linkage disequilibrium (LD) and sperm analysis within the MHC class II region show that crossovers are heavily clustered into 1-2 kb wide hotspots that profoundly influence LD patterns, with blocks of strongly-associated markers 10's of kb long lying between clusters of hotspots. Current evidence suggests that this mosaic pattern of recombining and non-recombining DNA is quite common elsewhere in the human genome. Other similar-width hotspots identified by sperm analysis have been found closely associated with minisatellites, where they appear to drive repeat DNA instability, and in the recombinationally active pseudoautosomal pairing region PAR1. While most hotspots engage in fully reciprocal crossover, one MHC hotspot shows reciprocal crossovers mapping to different locations. This asymmetry is most simply explained by SNPs influencing the efficiency of crossover initiation, with the result that markers near the site of initiation undergo biased gene conversion as a result of gap repair during recombination. This model is further supported by the occurrence of frequent conversion events without crossover at the centre of at least one hotspot. The emerging picture is that crossovers initiate at extremely localised sites in human chromosomes, and that the similar widths of hotspots may simply reflect similar processes of gap expansion and repair operating at different hotspots. Paradoxically, these hotspots appear to be prone to extinction by meiotic drive of variants that suppress recombination activity.

C. Ferec, V. Scotet, M. de Braekeleer, M. P. Audrézet;
EMI-U 0115 - C.H.U., Brest, FRANCE.

Cystic Fibrosis is the most frequent autosomal recessive disease among Caucasians. The disease, characterized by chronic broncho-pneumopathy and pancreatic insufficiency, is still fatal with a median life expectancy of about 30 years. Among the possible strategies for prevention is neonatal screening based on the expectation that early diagnosis leading to early treatment would result in lower morbidity and longer life expectancy. Thirteen years ago, we started a systematic neonatal screening program in Brittany, France, a region of 2.8 million inhabitants mostly of Celtic origin. The initial program was based on an IRT/IRT two-tier protocol (1989/1992) then we implemented a two-tier IRT/DNA analysis pilot program. During this 13 years period, 454 285 IRT tests were done on children born in Brittany and 163 were diagnosed with CF. The cumulative incidence of CF was one in 2787. The number of new cases identified each year is relatively constant (12/14). All the mutated CFTR alleles but one were characterized: 41 different mutations were identified corresponding to 48 different genotypes. During this period, 35% of these one-in-four risk couples opted for prenatal diagnosis and during the same period 10% of CF children were diagnosed in utero due to the discovery of an hyperechogenic bowel during pregnancy. We evidenced in this population study the spectacular changing epidemiology of CF
The possibility of direct benefits resulting from neonatal screening (with nutritional and respiratory benefits) raises the question of whether the time has arrived for routine neonatal screening for CF. We have shown the efficiency and the feasibility of neonatal screening for CF in Brittany based on 13 years experience. The IRT combined with mutation analysis on the same Guthrie cards can be done in any population in which most of the mutations can be identified. The implementation of a national neonatal screening program for CF has been decided by the health care authorities in France, the program has begun at the beginning of this year.

A. J. Clarke, E. Parsons, D. Bradley;
Department of Medical Genetics, University of Wales College of Medicine, Cardiff, Wales, UNITED KINGDOM.

The newborn screening programme in Wales has incorporated tests for Duchenne muscular dystrophy (DMD) since 1990 and for cystic fibrosis (CF) since 1997. Initial concerns that screening for DMD might lead to family disruption have not been justified, but we have learned lessons about screening for diseases where the affected child is not expected to benefit from early diagnosis.

The test must be perceived as optional by the midwife and family.
This requires an educational initiative for the community midwives.
Changes to service delivery may make more explicit the optional character of such non-therapeutic screening tests.
A protocol for handling positive screening test results must be developed and monitored.
Careful and sustained coordination of communication between the family, the primary health care team and specialist care is required.

Newborn screening for CF also identifies unaffected carrier infants, who will not benefit from their early diagnosis – they have elevated trypsin levels, one recognised CFTR mutation but normal sweat electrolytes. The recognition of these infants may be regarded as a disadvantage of screening, but does result in staging of the ‘bad news’ concerning affected infants. Should only those infants with two CFTR gene mutations be regarded as positive on the screening test ?
Our experiences have implications for the introduction of screening for additional disorders, such as MCAD deficiency. We have also found that a few infants have in the past been missed by the routine newborn screening programme. Newborn screening is not just a laboratory process.

Genetic Testing for Hereditary Colorectal Cancer in Children: Long-Term Psychological Effects

A. M. Codori, K. L. Zawacki, G. M. Petersen, D. L. Miglioretti, J. A. Bacon, J. D. Trimbath, S. V. Booker, K. Picarello, F. M. Giardiello;
Johns Hopkins Hospital, Baltimore, MD.

Children who carry a gene mutation for familial adenomatous polyposis (FAP) need annual screening for precancerous polyps and eventual cancer-preventing colectomy. Predictive genetic testing can identify children who need regular screening. Testing children for FAP has clear medical benefits, but the psychological effects have not been well studied. We evaluated the long-term psychological effects of genetic testing in 48 children and their parents. In each family, one parent was a known gene mutation carrier. Before genetic testing, and three times afterward, participants completed measures of psychological functioning, which, for children, included depression and anxiety symptoms, and behavior problems and competencies. Parents completed a measure of depression symptoms. Data were collected at 3-, 12-, and 23-55 months after disclosure. 22 children tested positive; 26 children tested negative. Mean length of follow-up was 38 months. There were no clinically-significant changes in mean psychological test scores in children or parents, regardless of the children’s test results. However, children who tested positive and had a mutation-positive sibling showed significant, but subclinical, increases in depression symptoms. Furthermore, several individual mutation-negative children with a positive sibling had clinical elevations in anxiety symptoms. Behavior problems declined for all groups, and behavior competence scores remained unchanged. We conclude that most children do not suffer clinically-significant psychological distress after testing. However, because some children showed clinically-significant anxiety symptoms, long-term psychological support should be available to those families with both mutation-positive and -negative children, and with multiple mutation-positive children. Our findings call for a multidisciplinary approach to genetic testing for children.

C. Barnes;
Genetics Centre, Guy's & St. Thomas' Hospital Trust, London, UNITED KINGDOM.

The advantages of performing a diagnostic genetic test, with proven medical benefits, on a symptomatic child is seldom questioned. Equally, there is a general consensus against testing healthy children for untreatable adult-onset genetic disorders. Genetic testing to determine the “carrier” status of a healthy child with a family history of a recessive or X-linked monogenic disorder or a balanced chromosome rearrangement, however, remains controversial. There are many views on this issue, and the parents' perspective can be very different from that of medical professionals, amongst whom opinions and practices vary. Also, the impact of carrier testing on children themselves remains a relatively unexplored area.
After an overview of the relevant literature to date, the response of one Genetics Centre to requests for the carrier testing of minors will be described and discussed.
A Position Statement on the genetic testing of children was devised in consultation with laboratory colleagues. This document was circulated to regional paediatricians, and supplied to other physicians on request. The document provides basic information about issues to consider in childhood testing and a summary of current departmental guidelines on the genetic testing of minors. The document explains why requests for carrier tests in children are no longer automatically accepted, and strongly encourages clinicians to refer parents requesting such tests for genetic counselling. An information leaflet for parents is also available.
It is hoped that such proactive initiatives can increase constructive dialogue between parents and professionals, and decrease the conflict that has often arisen in this area.

J. Goodship, D. Henderson;
Institute of Human Genetics, International Centre for Life, Newcastle upon Tyne, UNITED KINGDOM.

Understanding normal development is important to improved understanding of cardiovascular malformation (CVM). Development of the four chambered heart from a linear tube is a complex process. I will present current thinking that takes information from older studies but incorporates newer data using molecular markers and 3D reconstruction. Of particular importance is the ballooning model of development of the cardiac chambers from the primary heart tube. I will then illustrate, using three examples, how mutations in genes expressed at different stages of development lead to CVM. ZIC3 is a transcription factor with a role in early development. Mutations in ZIC3 lead to a range of heart defects associated with laterality disturbance demonstrating the importance of early events that establish midline and the left right axis to normal cardiac development. NKX2.5 is a cardiac specific homeobox gene and a homologue of Drosophila tinman. Mutations in this gene have been reported in patients with cardiac malformations and conduction defects. The third example is the mechanism by which elastin mutations lead to supravalvular aortic stenosis. Progress has been made in identifying genes implicated in CVM occurring in syndromes e.g. TBX5 in Holt Oram syndrome, TFAP2B in CHAR syndrome, PTPN11 in Noonan syndrome. However the vast majority of CVMs are isolated malformations. Diabetes is a known risk factor but other environmental factors have not yet been identified. Genetic factors are implicated as the recurrence risk is substantially higher than the population incidence but little progress has been made in identifying these genes. Cardiovascular malformations occur in 7/1000 livebirths; the challenge is to identify their causes.

H. Watkins;
John Radcliffe Hospital, University Department of Cardiovascular Medicine, Oxford, UNITED KINGDOM.

T. A. Cooper;
Baylor College of Medicine, Department of Pathology, Houston, TX.

A. de la Chapelle¹^,2;
¹Human Cancer Genetics Program, The Ohio State University, Columbus, OH, ²Folkhälsan Institute of Genetics, Helsinki, FINLAND.

When new genes with cancer significance are discovered it is reasonable to ask how and when the discovery can be translated into cancer therapy and prevention. Unfortunately, the most common answer is that we do not know. A more suitable question would seem to be whether novel genes will have any impact at all on cancer therapy.
In the academic world the great incentive that drives researchers is - in addition to curiosity if not passion - career aspects. Researchers will be credited for discoveries they make no matter whether the discoveries are ever translated into e.g. new drugs or treatment modalities.
In the commercial world the great incentive is money. Successful discoveries directly translate into money for all: the company, its employees, scientists, and shareholders.
How about the public, the cancer patient? The patient has more at stake than the researcher or the company. Luckily, whether a discovery has an impact on the clinical outcome is the ultimate measure of its success. Therefore, the efforts of academic researchers and companies can be said to ultimately focus on the patient, and almost nothing but the patient. This is fortunate, but progress has nevertheless been dismally slow. It would appear that every time a new research area is opened, hopes of ultimate translational success are high but in reality progress is slow. The recent breakthroughs in drug development targeting genetically determined defects have instilled high hopes. Another area showing promise is the molecular screening for inherited susceptibility to cancer. Lives can be saved and efforts can be optimized when clinical surveillance can be focused on those at high risk while those at low risk can be spared. It should not take many years before we know whether presently ongoing large investments - both academic and commercial - will pay off.