Preimplantation genetic diagnosis for retinoblastoma: the first reported liveborn

Impact of RB1 gene screening from blood collected on a single day from 411 family members of 113 Retinoblastoma survivors in India

OBJECTIVES

To analyse the profile and implication of genetic testing in a cohort of retinoblastoma (RB) patients and their families conducted on a single day during World Retinoblastoma Awareness Week 2017.

METHODS

Retrospective analysis of blood samples were collected from 411 subjects, including 113 probands at a camp organised for RB awareness and were analysed for RB1 mutations by Sanger sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA). If germline mutations were detected, the parents and siblings of the proband were tested for the same mutation.

RESULTS

Germline RB1 mutations were identified in 61/113(54%) probands with a mutation detection rate of 96% (47/49) and 22% (14/64) for bilateral and unilateral RB, respectively. Ten novel pathogenic mutations were identified. Splice mutation was most common (31%) followed by nonsense mutation (26%). The mean age at RB diagnosis was significantly lower in patients having germline RB1 mutation (mean 10.7 months ±2.5) compared to those without (mean 27.2 months ±6.5) (p = <0.0001). Parental transmission of the mutant allele was detected in 15/61(25%) cases of which 11(18%) parents were unaffected indicating incomplete penetrance. The origin of the variant allele was both paternal (n = 7) and maternal (n = 4) wherein 5 were bilateral and 6 unilateral.

CONCLUSIONS

The detection of a germline mutation impacts the proband and family members due to its implications on change in prognosis, frequency of subsequent evaluations, screening for ocular and non-ocular cancers, and surveillance of family and future progeny.

Preimplantation genetic testing for embryos predisposed to hereditary cancer: Possibilities and challenges

Preimplantation genetic testing (PGT), which was developed as an alternative to prenatal genetic testing, allows couples to avoid pregnancies with abnormal chromosomes and the subsequent termination of the affected fetus. Originally used for early onset monogenic conditions, PGT is now used to prevent various types of inherited cancer conditions based on the development of PGT technology, assisted reproductive techniques (ARTs), and in vitro fertilization (IVF). This review provides insights into the potential benefits and challenges associated with the application of PGT for hereditary cancer and provides an overview of the existing literature on this test, with a particular focus on the current challenges related to laws, ethics, counseling, and technology. Additionally, this review predicts the future potential applications of this method. Although PGT may be utilized to predict and prevent hereditary cancer, each case should be comprehensively evaluated. The motives of couples must be assessed to prevent the misuse of this technique for eugenic purposes, and non-pathogenic phenotypes must be carefully evaluated. Pathological cases that require this technology should also be carefully considered based on legal and ethical reasoning. PGT may be the preferred treatment for hereditary cancer cases; however, such cases require careful case-by-case evaluations. Therefore, this study concludes that multidisciplinary counseling and support for patients and their families are essential to ensure that PGT is a viable option that meets all legal and ethical concerns.

Ten things you learned in your residency about retinoblastoma that have changed the 2023 Victor T. Curtin Lecture

Retinoblatoma is now the pediatric cancer with the highest cure rate. More than any other ocular malignancy the approach to this cancer has changed dramatically in the past 10 years. Most of the things taught to the majority of all Ophthalmology residents is out of date. Because few Ophthalmologists deal with retinoblastoma they are not aware of these seismic changes so this summary of my Curtin lectures outlines some of the major changes all Ophthalmologists should be familiar with.

Neonatal Retinoblastoma

Retinoblastoma is the most common ocular malignancy of childhood. With an estimated 300 cases annually in the United States, retinoblastoma is nevertheless considered a rare tumor. Although retinoblastoma primarily affects younger children, diagnosis during the neonatal age range is less common. However, an understanding of patients at risk is critical for appropriate screening. Early detection and treatment by a multidisciplinary specialty team maximizes the chance for survival and ocular/vision salvage while minimizing treatment-related toxicity. Testing for alterations in the RB1 gene has become standard practice, and informs screening and genetic counseling recommendations for patients and their families.

Knudson to embryo selection: A story of the genetics of retinoblastoma

Retinoblastoma, the most common primary intraocular malignancy of the young, is a prototype hereditary cancer. Due to its fairly predictable Mendelian inheritance, easily examinable tumors, and early age of presentation, RB has served as the most extensively studied model for genetics in cancer. The genetic strides in RB have progressed at an exponential rate since the 1970s. The highly morbid, reasonably curable and distinctly predictable inheritance pattern of RB; not to mention its propensity to affect our young, forms the basis of aggressively encouraging genetic diagnosis in all patients of RB. In this article, we present the basic and clinically relevant concepts of the genetics retinoblastoma.

Prevention of Leber congenital amaurosis through preimplantation genetic diagnosis

Preimplantation genetic diagnosis can allow a family with a hereditary genetic mutation to conceive a disease-free child. We report the first published case of a child born without Leber congenital amaurosis through preimplantation genetic testing to a couple who had a son with a homozygous mutation in the GUCY2D gene.

Preimplantation genetic diagnosis as a strategy to prevent having a child born with an heritable eye disease

BACKGROUND

In developed countries, genetically inherited eye diseases are responsible for a high percentage of childhood visual impairment. We aim to report our experience using preimplantation genetic diagnostics (PGD) in order to avoid transmitting a genetic form of eye disease associated with childhood visual impairment and ocular cancer.

MATERIAL AND METHODS

Retrospective case series of women who underwent in vitro fertilization (IVF) and PGD due to a familial history of inherited eye disease and/or ocular cancer, in order to avoid having a child affected with the known familial disease. Each family underwent genetic testing in order to identify the underlying disease-causing mutation. IVF and PGD treatment were performed; unaffected embryos were implanted in their respective mothers.

RESULTS

Thirty-five unrelated mothers underwent PGD, and the following hereditary conditions were identified in their families: albinism (10 families); retinitis pigmentosa (7 families); retinoblastoma (4 families); blue cone monochromatism, achromatopsia, and aniridia (2 families each); and Hermansky-Pudlak syndrome, Leber congenital amaurosis, Norrie disease, papillorenal syndrome, primary congenital cataract, congenital glaucoma, Usher syndrome type 1F, and microphthalmia with coloboma (1 family each). Following a total of 88 PGD cycles, 18 healthy (i.e., unaffected) children were born.

CONCLUSIONS

Our findings underscore the importance an ophthalmologist plays in informing patients regarding the options now available for using prenatal and preimplantation genetic diagnosis to avoid having a child with a potentially devastating genetic form of eye disease or ocular cancer. This strategy is highly relevant, particularly given the limited options currently available for treating these conditions.

Knowledge, experiences and attitudes concerning genetics among retinoblastoma survivors and parents

Clinical genetic services are increasingly providing a more nuanced understanding of genetic disease diagnostics and future risk for patients. Effectively conveying genetic information is essential for patients to make informed decisions. This is especially important for survivors of heritable cancers such as retinoblastoma (childhood eye cancer), where survivors who carry a germline mutation in the RB1 gene are at increased risk of second cancers in adulthood, and of passing on the disease risk to future offspring. We conducted focus groups with adult survivors of retinoblastoma and parents of children with retinoblastoma, to uncover their knowledge of, experiences with and attitudes about retinoblastoma genetics and related impacts of the cancer. Results revealed that participants understood that retinoblastoma was a genetic disease, but often misunderstood the implications of genetics on cancer phenotype and risk. Experiences with genetic testing and counseling were generally positive, however, participants reported challenges in accessing genetic information and psychosocial support. Participants suggested more educational resources, peer-to-peer counseling, and psychosocial support would enhance uptake of important genetic information. The results of the study will inform patient-oriented approaches to deliver comprehensive genetic healthcare.

A Fluorescent Quantitative Multiplex PCR Method to Detect Copy Number Changes in the RB1 Gene

Copy number changes comprising deletions or insertions involving single or multiple exons of a gene are known to occur in a significant proportion of cases in retinoblastoma. The protocol described here involves a two-step quantitative multiplex PCR process which is suitable for the detection of such mutations in the RB1 as well as in other genes. This is achieved through the use of suitable gene-specific primers designed to amplify individual exons, with universal tags attached to the 5' end of each primer. These tagged primers are used in the first step of PCR of the RB1 gene in patients. The second step is carried out through the use of "universal" primers complementary to the tag sequences alone. This technique facilitates the detection of fluorescent PCR products from multiple exons through the use of a single fluorescent tagged primer.

"Where Does it Come from?" Experiences Among Survivors and Parents of Children with Retinoblastoma in Kenya

Genetic testing and counseling have become integral to the timely control of heritable cancers, like the childhood eye cancer retinoblastoma. This study aimed to determine attitudes, knowledge and experiences related to retinoblastoma genetics, among survivors and parents of children with retinoblastoma in Kenya. This qualitative study used focus groups as the primary data collection method, coupled with a brief demographic questionnaire. Study settings were Kenyatta National Hospital and Presbyterian Church of East Africa Kikuyu Hospital. Thematic analysis was used to identify key themes. Thirty-one individuals participated in five focus groups. Two main concepts emerged: (1) the origins of retinoblastoma are unclear, and (2) retinoblastoma is associated with significant challenges. The lack of clarity surrounding the origins of retinoblastoma was linked to limited knowledge of retinoblastoma genetics, and limited genetic counseling delivery and uptake. The challenges associated with retinoblastoma were discussed in terms of the impact of the diagnosis on individuals and families, and unmet healthcare needs related to the diagnosis. Next steps will incorporate these findings to develop evidence-informed and accessible cancer genetic services in Kenya.

Mutation spectrum of RB1 mutations in retinoblastoma cases from Singapore with implications for genetic management and counselling

Retinoblastoma (RB) is a rare childhood malignant disorder caused by the biallelic inactivation of RB1 gene. Early diagnosis and identification of carriers of heritable RB1 mutations can improve disease outcome and management. In this study, mutational analysis was conducted on fifty-nine matched tumor and peripheral blood samples from 18 bilateral and 41 unilateral unrelated RB cases by a combinatorial approach of Multiplex Ligation-dependent Probe Amplification (MLPA) assay, deletion screening, direct sequencing, copy number gene dosage analysis and methylation assays. Screening of both blood and tumor samples yielded a mutation detection rate of 94.9% (56/59) while only 42.4% (25/59) of mutations were detected if blood samples alone were analyzed. Biallelic mutations were observed in 43/59 (72.9%) of tumors screened. There were 3 cases (5.1%) in which no mutations could be detected and germline mutations were detected in 19.5% (8/41) of unilateral cases. A total of 61 point mutations were identified, of which 10 were novel. There was a high incidence of previously reported recurrent mutations, occurring at 38.98% (23/59) of all cases. Of interest were three cases of mosaic RB1 mutations detected in the blood from patients with unilateral retinoblastoma. Additionally, two germline mutations previously reported to be associated with low-penetrance phenotypes: missense-c.1981C>T and splice variant-c.607+1G>T, were observed in a bilateral and a unilateral proband, respectively. These findings have implications for genetic counselling and risk prediction for the affected families. This is the first published report on the spectrum of mutations in RB patients from Singapore and shows that further improved mutation screening strategies are required in order to provide a definitive molecular diagnosis for every case of RB. Our findings also underscore the importance of genetic testing in supporting individualized disease management plans for patients and asymptomatic family members carrying low-penetrance, germline mosaicism or heritable unilateral mutational phenotypes.

Genetics and Molecular Diagnostics in Retinoblastoma--An Update

Retinoblastoma is the prototype genetic cancer: in one or both eyes of young children, most retinoblastomas are initiated by biallelic mutation of the retinoblastoma tumor suppressor gene, RB1, in a developing retinal cell. All those with bilateral retinoblastoma have heritable cancer, although 95% have not inherited the RB1 mutation. Non-heritable retinoblastoma is always unilateral, with 98% caused by loss of both RB1 alleles from the tumor, whereas 2% have normal RB1 in tumors initiated by amplification of the MYCN oncogene. Good understanding of retinoblastoma genetics supports optimal care for retinoblastoma children and their families. Retinoblastoma is the first cancer to officially acknowledge the seminal role of genetics in cancer, by incorporating "H" into the eighth edition of cancer staging (2017): those who carry the RB1 cancer-predisposing gene are H1; those proven to not carry the familial RB1 mutation are H0; and those at unknown risk are HX. We suggest H0* be used for those with residual <1% risk to carry a RB1 mutation due to undetectable mosaicism. Loss of RB1 from a susceptible developing retinal cell initiates the benign precursor, retinoma. Progressive genomic changes result in retinoblastoma, and cancer progression ensues with increasing genomic disarray. Looking forward, novel therapies are anticipated from studies of retinoblastoma and metastatic tumor cells and the second primary cancers that the carriers of RB1 mutations are at high risk to develop. Here, we summarize the concepts of retinoblastoma genetics for ophthalmologists in a question/answer format to assist in the care of patients and their families.

Prenatal genetic diagnosis of retinoblastoma and report of RB1 gene mutation from India

BACKGROUND

Retinoblastoma is the most common intraocular malignancy of childhood. There is a paucity of genetic testing and prenatal genetic diagnosis from India, which has the highest incidence worldwide.

MATERIALS AND METHODS

RB1 gene screening of an 8-month-old female child with bilateral retinoblastoma was accomplished using next generation sequencing. The results were used for prenatal testing in this family.

RESULTS

A heterozygous germline mutation (chr13: 48951119delA; c.1281delA) was detected, which resulted in premature termination of a protein product (p.Glu428Argfs*29). Prenatal testing in maternal DNA revealed carrier status of the mother. Further clinical examination in the family members revealed retinocytomas in both eyes of the mother and maternal grandmother. Prenatal genetic testing of the developing fetus showed positivity for the mutation. As the family preferred to continue the pregnancy, serial 3-D ultrasounds were carried out every 2 weeks in the third trimester. Ten days after delivery, small extrafoveal tumors developed in both eyes, which were then treated successfully with transpupillary thermotherapy.

CONCLUSION

We report the significance of genetic testing in the early detection and management of retinoblastoma from India.

Retinoblastoma

Retinoblastoma is a rare cancer of the infant retina that is diagnosed in approximately 8,000 children each year worldwide. It forms when both retinoblastoma gene (RB1) alleles are mutated in a susceptible retinal cell, probably a cone photoreceptor precursor. Loss of the tumour-suppressive functions of the retinoblastoma protein (pRB) leads to uncontrolled cell division and recurrent genomic changes during tumour progression. Although pRB is expressed in almost all tissues, cone precursors have biochemical and molecular features that may sensitize them to RB1 loss and enable tumorigenesis. Patient survival is >95% in high-income countries but <30% globally. However, outcomes are improving owing to increased disease awareness for earlier diagnosis, application of new guidelines and sharing of expertise. Intra-arterial and intravitreal chemotherapy have emerged as promising methods to salvage eyes that with conventional treatment might have been lost. Ongoing international collaborations will replace the multiple different classifications of eye involvement with standardized definitions to consistently assess the eligibility, efficacy and safety of treatment options. Life-long follow-up is warranted, as survivors of heritable retinoblastoma are at risk for developing second cancers. Defining the molecular consequences of RB1 loss in diverse tissues may open new avenues for treatment and prevention of retinoblastoma, as well as second cancers, in patients with germline RB1 mutations.

Management of retinoblastoma in children: current status

In recent years, there have been dramatic changes in the management of intraocular retinoblastoma. Intraocular retinoblastoma is a highly curable malignancy and current treatments are aimed to preserve vision while reducing the late effects such as treatment-induced secondary malignancies. The advent of intra-arterial chemotherapy changed the treatment paradigm from systemic treatment with chemotherapy to local treatment, and new questions emerged. While intra-arterial chemotherapy achieved encouraging results, only experience from major referral centers is reported, so its indications, advantages and risks are still to be elucidated. Many factors should be considered when choosing the appropriate conservative therapy. When the disease has extended outside the eye, the chances of cure are significantly lower and treatment should be tailored by the presence of pathology risk factors such as invasion of the choroid, the optic nerve, and the sclera. Adjuvant therapy is decided upon this information. Children with overt extraocular disease are treated with higher dose neoadjuvant therapy followed by delayed enucleation and adjuvant therapy.

Novel mutations in the RB1 gene from Chinese families with a history of retinoblastoma

Retinoblastoma is an aggressive eye cancer that develops during infancy and is divided into two clinical types, sporadic and heritable. RB1 has been identified as the only pathological gene responsible for heritable retinoblastoma. Here, we identified 11 RB1 germline mutations in the Han pedigrees of 17 bilateral retinoblastoma patients from China. Four mutations were nonsense mutations, five were splice site mutations, and two resulted in a frame shift due to an insertion or a deletion. Three of the mutations had not been previously reported, and the p.Q344L mutation occurred in two generations of retinoblastoma patients. We investigated phenotypic-genotypic relationships for the novel mutations and showed that these mutations affected the expression, location, and function of the retinoblastoma protein. Abnormal protein localization was observed after transfection of the mutant genes. In addition, changes in the cell cycle distribution and apoptosis rates were observed when the Saos-2 cell line was transfected with plasmids encoding the mutant RB1 genes. Our findings expand the spectrum of known RB1 mutations and will benefit the investigation of RB1 mutation hotspots. Genetic counseling can be offered to families with heritable RB1 mutations.

[Malignant neoplasms in the neonate]

Cancer in children has characteristics that differentiate it from other types reported in later ages. Overall survival at 3 years is up to 70% depending on the tumor studied. Major organs and systems affected are the hematopoietic system, central nervous system and sympathetic and mesenchymal tissues. The increased incidence of neonatal tumors observed in this and other studies is based on the increasing number of solid tumors (teratomas and neuroblastomas) because cases of central nervous system tumors and leukemias have remained constant. Ultrasonography is the first line of approach and can detect up to 70% of fetal anomalies. The physiology of the newborn causes the necessary multidisciplinary treatment in neoplastic disease to be modified substantially in this age group to avoid toxicity and sequelae. The most common treatment is surgery. Achieving timely diagnostic treatment options are effective in improving the survival of these patients.

Animal models in retinoblastoma research

Advances in animal models of retinoblastoma have accelerated research in this field, aiding in understanding tumor progression and assessing therapeutic modalities. The distinct pattern of mutations and specific location of this unique intraocular tumor have paved the way for two types of models- those based on genetic mutations, and xenograft models. Retinoblastoma gene knockouts with an additional loss of p107, p130, p53 and using promoters of Nestin, Chx10, and Pax6 genes show histological phenotypic changes close to the human form of retinoblastoma. Conditional knockout in specific layers of the developing retina has thrown light on the origin of this tumor. The use of xenograft models has overcome the obstacle of time delay in the presentation of symptoms, which remains a crucial drawback of genetic models. With the advances in molecular and imaging technologies, the current research aims to develop models that mimic all the features of retinoblastoma inclusive of its initiation, progression and metastasis. The combination of genetic and xenograft models in retinoblastoma research has and will help to pave way for better understanding of retinoblastoma tumor biology and also in designing and testing effective diagnostic and treatment modalities.

Update on pediatric cancer predisposition syndromes

Hereditary cancer syndromes in children and adolescents are becoming more recognized in the field of pediatric hematology/oncology. A recent workshop held at the American Society of Pediatric Hematology/Oncology (ASPHO) 2012 Annual Meeting included several interactive sessions related to specific familial cancer syndromes, genetic testing and screening, and ethical issues in caring for families with inherited cancer risk. This review highlights the workshop presentations, including a brief background about pediatric cancer predisposition syndromes and the importance of learning about them for the practicing pediatric hematologists/oncologists. This is followed by a brief summary of the newly described cancer predisposition syndromes including Rhabdoid Tumor Predisposition Syndrome, Hereditary Paragangliomas and Pheochromocytoma Syndrome, and Familial Pleuropulmonaryblastoma Tumor Predisposition (DICER1) Syndrome. The next section covers genetic testing and screening for pediatric cancer predisposition syndromes. Ethical issues are also discussed including preimplantation genetic diagnosis or testing (PGD/PGT), suspicious lesions found on tumor screening, and incidental mutations discovered by whole genome sequencing. Finally, the perspective of a family with Li-Fraumeni Syndrome is shared.

Evaluation of the prenatally diagnosed mass

With the advent of advanced imaging technologies, the field of prenatal diagnosis and counseling has grown rapidly. The use of fetal ultrasound and ultrafast magnetic resonance imaging has allowed for prenatal identification of structural anomalies as well as neoplasm. The differential diagnosis of a fetal mass is dependent upon its location and the tissue characteristics of the mass on imaging. The use of amniocentesis for chromosomal analysis and genetic testing for known tumor-related genetic abnormalities may aid in further refining the diagnosis. Herein we describe a general diagnostic algorithm for fetal masses based upon their location within the body and how the appropriate diagnostic modalities may be applied in the clinical setting.

Retinoblastoma in the perinatal and neonatal child

Retinoblastoma is a rare primary intraocular malignancy. Presentation in the neonatal period is not common. With improved genetic testing, screening of the unborn child and neonate is taking on a greater role in the management of these patients. Treatment of retinoblastoma in the neonate is complex and requires a multidisciplinary and highly individualized approach. If possible, focal modalities should be used and external beam radiation avoided. Systemic intravenous chemotherapy may be necessary with regimens including carboplatin, vincristine and etoposide. Such cases are best managed by specialist centers with access to experts in oncology, ophthalmology, radiation therapy, genetics, pathology and anesthesia.

Genetics of primary intraocular tumors

Primary intraocular neoplasms are tumors that originate within the eye. The most common malignant primary intraocular tumor in adults is uveal melanoma and the second is primary intraocular lymphoma or vitreoretinal (intraocular) lymphoma. The most common malignant intraocular tumor in children is retinoblastoma. Genetics plays a vital role in the diagnosis and detection of ocular tumors. In uveal melanoma, monosomy 3 is the most common genetic alteration and somatic mutations of BAP1, a tumor suppressor gene, have been reported in nearly 50% of primary uveal melanomas. The retinoblastoma gene RB1 is the prototype tumor suppressor gene-mutations in RB1 alleles lead to inactivated RB protein and the development of retinoblastoma. Immunoglobulin heavy chain (IgH) or T-cell receptor (TCR) gene rearrangement is observed in B-cell or T-cell primary vitreoretinal lymphoma, respectively. Other factors related to the genetics of these three common malignancies in the eye are discussed and reviewed.

Retinoblastoma major review with updates on Middle East management protocols

Many advances in the field of management of retinoblastoma emerged in the past few years. Patterns of presentation of retinoblastoma in the Middle East region differ from Western community. The use of enucleation as a radical method of eradicating advanced disease is not easily accepted by patient's family. We still do see stage E, failed or resistant retinoblastoma and advanced extraocular disease ensues as a result of delayed enucleation decision. In this review, we discuss updates in management of retinoblastoma with its implication on patients in our part of the world. Identifying clinical and high risk characteristics is important prognostically and are discussed for further management of retinoblastoma cases.

Attitudes toward childbearing and prenatal testing in individuals undergoing genetic testing for Lynch syndrome

To examine attitudes toward childbearing and prenatal genetic testing among individuals at risk for Lynch syndrome (LS), the most common type of hereditary colorectal cancer. Individuals undergoing clinical genetic testing for mismatch repair (MMR) gene mutations completed written questionnaires before and after testing. 161 of 192 (84%) eligible individuals participated in the study. Mean age was 46 years (range 20-75), 71% were female, 53% had a personal diagnosis of cancer, and 68% had children. Eighty percent worried about their children's risk for developing cancer; however only 9% reported their decision to have children was affected by their family history of cancer. When asked whether providing prenatal testing to carriers of MMR gene mutations was ethical, 66% (86/130) of respondents agreed/strongly agreed, 25% (32) were neutral and 9% (12) disagreed/strongly disagreed. Of 48 individuals planning to have children in the future, 57% (27) intended to have children regardless of their genetic test result. If found to carry a MMR gene mutation that confirmed LS, 42% (20) would consider prenatal testing for a future pregnancy and 20% (7/35) of women would consider having children earlier in order to have prophylactic surgery to reduce their risk for gynecologic cancers. Individuals undergoing genetic testing for LS may utilize test results to make reproductive decisions. Clinicians should be prepared to discuss options of reproductive genetic technologies during counseling of LS patients of childbearing age.

Role of genetic testing in retinoblastoma management at a tertiary referral centre

BACKGROUND

Retinoblastoma (MIM +180 200) is a malignant neoplasm affecting embryonal retina, associated with mutations in the RB1 gene. This paper investigates the results of RB1 testing in retinoblastoma management in a tertiary referral centre.

METHODS

A retrospective audit of genetic testing for retinoblastoma from 2003 to 2008, to determine epidemiology, rate of mutation detection and spectrum was undertaken. Eligible probands were identified from the department database and hospital records examined. DNA extracted from tumour tissue and/or peripheral blood was analysed. All patients and families underwent genetic counselling.

RESULTS

Twenty patients, including one family, were identified. Eight had bilateral tumours, of whom seven presented before 2 years of age, whereas 10 of 12 unilateral cases presented after 2 years of age. Ten patients (50%) were European, four Maori (20%), three Pacific (15%), two Asian (10%), and one of mixed ancestry (5%). Genetic analysis achieved mutation detection on all affected alleles of all the patients, with tumour tissue available for testing in 19 cases. Ten (40%) had germline mutations (eight bilateral and two unilateral), including one mosaic. 75% of affected Maori had germline mutations compared with 40% Europeans. A wide range of mutations was detected with one novel mutation identified in a familial case.

CONCLUSION

Advances in gene testing have enabled a high rate of mutation detection, particularly when tumour tissue is genotyped. Genetic analysis is integral to the management of retinoblastoma patients allowing enhanced follow-up care, avoidance of unnecessary examinations, family screening, counselling and reproductive planning, with early tumour detection in predisposed individuals.

A comprehensive, sensitive and economical approach for the detection of mutations in the RB1 gene in retinoblastoma

Retinoblastoma (Rb) is the most common primary intraocular malignancy in children. It is brought about by the mutational inactivation of both alleles of RB1 gene in the developing retina. To identify the RB1 mutations, we analysed 74 retinoblastoma patients by screening the exons and the promoter region of RB1. The strategy used was to detect large deletions/duplications by fluorescent quantitative multiplex PCR; small deletions/insertions by fluorescent genotyping of RB1 alleles, and point mutations by PCR-RFLP and sequencing. Genomic DNA from the peripheral blood leucocytes of 74 Rb patients (53 with bilateral Rb, 21 with unilateral Rb; 4 familial cases) was screened for mutations. Recurrent mutations were identified in five patients with bilateral Rb, large deletions in 11 patients (nine with bilateral Rb and two with unilateral Rb), small deletions/insertions were found in 12 patients all with bilateral Rb, and point mutations in 26 patients (14 nonsense, six splice site, five substitution and one silent change). Three mutations were associated with variable expressivity of the disease in different family members. Using this method, the detection rates achieved in patients with bilateral Rb were 44/53 (83%) and with unilateral Rb, 5/21 (23.8%). This approach may be feasible for clinical genetic testing and counselling of patients.

Preimplantation genetic diagnosis for stargardt disease

PURPOSE

To report the first use of in vitro fertilization (IVF) and preimplantation genetic diagnosis to achieve an unaffected pregnancy in an autosomal-recessive retinal dystrophy.

DESIGN

Case report.

METHODS

An affected male with Stargardt disease and his carrier wife underwent IVF. Embryos obtained by intracytoplasmic sperm injection underwent single-cell DNA testing via polymerase chain reaction and restriction enzyme analysis to detect the presence of ABCA4 mutant alleles. Embryos were diagnosed as being either affected by or carriers for Stargardt disease. A single carrier embryo was implanted.

RESULTS

Chorionic villus sampling performed during the first trimester verified that the fetus possessed only 1 mutant paternal allele and 1 normal maternal allele, thus making her an unaffected carrier of the disease. A healthy, live-born female was delivered.

CONCLUSION

IVF and preimplantation genetic diagnosis can assist couples with an affected spouse and a carrier spouse with recessive retinal dystrophies to have an unaffected child.

Preimplantation genetic diagnosis for BRCA1 exon 13 duplication mutation using linked polymorphic markers resulting in a live birth

BACKGROUND

The risk of breast cancer associated with inheriting a BRCA1 mutation is extremely high, in addition, there is a 50% chance of transmitting this familial cancer mutation to any offspring.

METHODS

A 31-year-old woman with a strong maternal family history of early onset of breast cancer had experienced 3 years of primary infertility. Presymptomatic testing confirmed the woman had inherited a 6 kb duplication of exon 13 (ins6KbEx13) in BRCA1 from her mother. Neither gamete donation or adoption were acceptable options for this infertile couple, and as termination of pregnancy after prenatal diagnosis following in vitro fertilization (IVF) was not ethically acceptable, preimplantation genetic diagnosis (PGD) was sought. A single-cell PCR protocol for PGD for the breast and ovarian cancer predisposing BRCA1 exon 13 duplication mutation was developed which involved amplification of three specific gene regions, including the BRCA1 mutation (ins6KbEx13), an intragenic marker (D17S855) and a flanking marker (D17S1185).

RESULTS

In the first cycle of IVF, three embryos were analyzed and two were determined to be at low risk of having inherited the maternal BRCA1 mutation. Following the transfer of both embryos on day 5, a singleton pregnancy resulted. Declining confirmatory prenatal diagnosis, a male baby was subsequently delivered at term.

CONCLUSIONS

Successful PGD for BRCA1 resulted in the delivery of a live-born male. PGD using linked polymorphic markers provides an alternate option for reproduction for couples with or at risk of having inherited a BRCA1 mutation.

Strategies and outcomes of PGD of familial adenomatous polyposis

Owing to adult onset of hereditary cancer, prenatal diagnosis (PND) raises numerous ethical issues on the acceptability to terminate an affected pregnancy (TOP). PND for these disorders is often considered as unacceptable by couples as well as geneticists and legal or ethical authorities, but preimplantation genetic diagnosis (PGD), even if subject to controversy, seems to be a more acceptable option. Therefore, many couples, who do not want to transmit their cancer to their children, consider PGD as their only reproductive option. This article describes our experience of PGD for familial adenomatous polyposis (FAP). Twelve couples were referred between 2000 and 2005. We developed PGD tests to detect the mutation alone, but we rapidly set up multiplex PCR combining mutation detection and indirect diagnosis. Finally, we set up duplex and triplex indirect diagnoses to be able to offer a PGD, whatever mutation was involved in familial cases. PGD strategies were based on (i) a new double allele-specific PCR approach (D-ARMS) allowing the detection of the wild-type and mutated allele; (ii) PCR fragments sizing and (iii) restriction length polymorphisms. For the 12 referrals, we developed eight tests, and 11 cycles have been performed for four couples, resulting in eight embryo transfers and five pregnancies, with the birth of one healthy boy and two ongoing pregnancies. We are now able to propose PGD to most couples at risk of transmitting FAP to their offspring, whether the mutation is familial or occurred de novo.

Diagnosis and current management of retinoblastoma

Retinoblastoma represents the prototypic model for inherited cancers. The RB1 gene was the first tumor suppressor gene to be identified. It represents the most frequent primary eye cancer in children under 15 years old, habitually occurring in infancy, even in utero, but can be observed in older children or young adults. Many other retinal lesions may also simulate retinoblastoma. The two major presenting signs are leukocoria and strabismus, but other ocular or general signs may be observed. A highly malignant tumor, retinoblastoma can nowadays be cured. The heritable form, however, carries a high risk of second nonocular tumors. Treatment in the early stages of disease holds a good prognosis for survival and salvage of visual function. In very late stages, however, the prognosis for ocular function and even survival is jeopardized.

Retinoblastoma

Retinoblastoma is a rare eye tumor of childhood that arises in the retina. It is the most common intraocular malignancy of infancy and childhood; with an incidence of 1/15,000–20,000 live births. The two most frequent symptoms revealing retinoblastoma are leukocoria and strabismus. Iris rubeosis, hypopyon, hyphema, buphthalmia, orbital cellulites and exophthalmia may also be observed. Sixty per cent of retinoblastomas are unilateral and most of these forms are not hereditary (median age at diagnosis two years). Retinoblastoma is bilateral in 40% of cases (median age at diagnosis one year). All bilateral and multifocal unilateral forms are hereditary. Hereditary retinoblastoma constitutes a cancer predisposition syndrome: a subject constitutionally carrying an RB1 gene mutation has a greater than 90% risk of developing retinoblastoma but is also at increased risk of developing other types of cancers. Diagnosis is made by fundoscopy. Ultrasound, magnetic resonance imaging (MRI) and computed tomography (CT) scans may contribute to diagnosis. Management of patients with retinoblastoma must take into account the various aspects of the disease: the visual risk, the possibly hereditary nature of the disease, the life-threatening risk. Enucleation is still often necessary in unilateral disease; the decision for adjuvant treatment is taken according to the histological risk factors. Conservative treatment for at least one eye is possible in most of the bilateral cases. It includes laser alone or combined with chemotherapy, cryotherapy and brachytherapy. The indication for external beam radiotherapy should be restricted to large ocular tumors and diffuse vitreous seeding because of the risk of late effects, including secondary sarcoma. Vital prognosis, related to retinoblastoma alone, is now excellent in patients with unilateral or bilateral forms of retinoblastoma. Long term follow-up and early counseling regarding the risk of second primary tumors and transmission should be offered to retinoblastoma patients.

Preimplantation genetic diagnosis

This article covers the rapidly advancing field of preimplantation genetic diagnosis (PGD), the molecular genetic analysis of cells taken from embryos formed through in vitro fertilization (IVF). The article focuses on current practices in patient management, relevant IVF and PGD procedures, molecular methods used in the genetic analysis, and technical difficulties that can affect test results. It discusses the growing list of indications for PGD including chromosomal disorders, monogenic disorders and human leukocyte antigen typing typing of embryos. The article also examines some of the emerging technologies being introduced into PGD.

Application of genetic approaches to ocular disease

The human eye is a complex organ whose development requires extraordinary coordination of developmental processes. Multiple genes responsible for the proper development and maintenance of the vertebrate eye have been identified and shown to be involved in a variety of debilitating ocular conditions. Genetic diseases involving the eye represent a leading cause of blindness in children and adults. This article summarizes current genetic approaches and their application to studies of ocular disease.

Cancer genetic testing and assisted reproduction

PURPOSE

Because of increasing uptake of cancer genetic testing and the improving survival of young patients with cancer, health care practitioners including oncologists will increasingly be asked about options for assisted reproduction by members of families affected by hereditary cancer syndromes. Among these reproductive options, preimplantation genetic diagnosis (PGD) offers the opportunity to select embryos without familial cancer-predisposing mutations.

METHODS

A review of the published literature supplemented by a survey of PGD centers in the United States.

RESULTS

Prenatal diagnosis and/or embryo selection after genetic testing has already been performed in the context of more than a dozen familial cancer syndromes, including the common syndromes of genetic predisposition to colon and breast cancer.

CONCLUSION

While constituting new reproductive options for families affected by cancer, the medical indications and ethical acceptance of assisted reproductive technologies for adult-onset cancer predisposition syndromes remain to be defined. Continued discussion of the role of PGD in the reproductive setting is needed to inform the responsible use of these technologies to decrease the burden of heritable cancers.

Unilateral retinoblastoma, lack of familial history and older age does not exclude germline RB1 gene mutation

Conclusive identification of RB1 mutations in retinoblastoma is predicted to improve the clinical management of affected children and relatives. However, despite clear clinical benefits, RB1 screening remains difficult, most of the alterations being unique and randomly distributed throughout the entire coding sequence. In this report, we present the results of a constitutional RB1 analysis undertaken in our institution over the last four years. The detection of RB1 gene deletion or mutation was performed by Southern blot and sequence analyses in 73 patients (including three families with 2, 3 and 3 probands, respectively). Complementary constitutional chromosome and fluorescent in situ hybridization (FISH) analyses of RB1 gene were applied in cases where hereditary retinoblastoma was suspected despite negative detection. Altogether, germline abnormalities were found in 11% (4/36 patients) of sporadic unilateral retinoblastoma (median age, 21.5 months) and 86% (32/37 patients) of sporadic bilateral or positive familial history retinoblastoma (median age, 5 months). The spectrum of germline alterations found in 31 distinct families included 12 nonsense mutations (39%); 10 point insertions or deletions with frameshift (32%); 4 mutations and 1 deletion affecting splice sites (16%); 2 missense mutations (6%); and 2 large deletions (6%). A total of 15 mutations have not been previously reported. In this small series, splicing mutations were associated with bilateral disease whilst most of the frameshift mutations were identified in patients with an early age at diagnosis, bilateral disease or hereditary forms of the disease. This study confirms that screening for constitutional RB1 mutation should become an integral part of current management of any patient affected by retinoblastoma irrespective of the tumour laterality and familial background.