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Uniparental disomy

Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent. UPD can occur as a random event during the formation of egg or sperm cells or may happen in early fetal development. more...

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In many cases, UPD likely has no effect on health or development. Because most genes are not imprinted, it doesn’t matter if a person inherits both copies from one parent instead of one copy from each parent. In some cases, however, it does make a difference whether a gene is inherited from a person’s mother or father. A person with UPD may lack any active copies of essential genes that undergo genomic imprinting. This loss of gene function can lead to delayed development, mental retardation, or other medical problems.

The most well-known conditions include Prader-Willi syndrome and Angelman syndrome. Both of these disorders can be caused by UPD or other errors in imprinting involving genes on the long arm of chromosome 15. Other conditions, such as Beckwith-Wiedemann syndrome, are associated with abnormalities of imprinted genes on the short arm of chromosome 11.

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AAFP Core Educational Guidelines - Statistical Data Included
From American Family Physician, 7/1/99

Medical Genetics

Recommended core educational guidelines for family practice residents This document has been endorsed by the American Academy of Family Physicians and was developed in cooperation with the American College of Medical Genetics, the Association of Professors of Human and Medical Genetics, the Association of Departments of Family Medicine, the Association of Family Practice Residency Directors and the Society of Teachers of Family Medicine. Attitudes

The resident should develop attitudes that encompass the following:

A. Recognition of the importance of the family physician, the medical geneticist and the genetics team as collaborators in the evaluation, diagnosis and management of patients referred for genetic consultation.

B. Recognition of the need for sensitivity to the patient's and family's concerns relating to referral for genetic evaluation and diagnosis of a genetic disorder.

C. Recognition of the importance of confidentiality, ethical and legal issues involved in medical genetics.

Knowledge A. Basic principles of human and medical genetics

1. Genes and chromosomes

2. Genogram/pedigree

a. Components b. Preparation c. Interpretation

3. Basic Mendelian inheritance patterns (hair/eye color, blood type) a. Autosomal dominant b. Autosomal recessive c. X-linked dominant d. X-linked recessive

4. Non-Mendelian inheritance patterns a. Multifactorial b. Mitochondrial (MELAS) c. Trinucleotide repeats (fragile X syndrome, Huntington's disease) d. Imprinting (Prader-Willi syndrome, Angelman's syndrome) e. Uniparental disomy (Prader-Willi syndrome, Angelman's syndrome)

B. Ethical and legal considerations/controversies

1. Screening for genetic abnormalities

2. Prenatal-preconception testing

3. Presymptomatic genetic testing (breast cancer, Huntington's disease)

4. Carrier testing for genetic disorders

5. Confidentiality

6. Risk assessment

7. Responsibility to inform

8. Discrimination issues (insurance coverage, employment)

9. Informed consent

10. Paternity determinations

C. Terminology used in medical genetics (mosaicism, incomplete penetrance, variable expressivity, pleomorphic, malformation, deformation, disruption, dysmorphic, minor/major anomaly, homozygote, heterozygote, allele, polymorphism)

D. Laboratory studies and research

1. Karyotype

2. Fluorescent in situ hybridization

3. Polymerase chain reaction, sequencing, mutation detection

4. Gene mapping

E. Limitations of genetic testing (polymorphism versus mutation)

F. The genetic implications of common disorders and conditions

1. Chromosomal abnormalities

a. Trisomy (13, 18 and 21 [Down syndrome]) b. Sex chromosome anomalies (Turner's syndrome, Klinefelter's syndrome) c. Translocations, inversions, deletions d. Microdeletion syndromes e. Cri du chat syndrome

2. Familial variants a. Congenital short stature b. Delayed-onset puberty

3. Oncology a. Colon cancer b. Breast cancer c. Ovarian cancer d. Prostate cancer e. Wilms' tumor f. Retinoblastoma g. Familial ademomatous polyposis

4. Geriatric disorders a. Alzheimer's disease b. Parkinson's disease

5. Metabolic disorders a. Endocrine (diabetes, thyroid) b. Amino acids (phenylketonuria, maple syrup urine disease) c. Organic acids d. Fatty acid oxidation e. Energy metabolism f. Lysosomal storage (Tay-Sachs disease) g. Syndrome "X" h. Lipid disorders i. Biotinidase deficiency j. Growth hormone deficiency k. Precocious puberty l. Alpha1-antitrypsin deficiency

6. Skeletal/connective tissue abnormalities a. Talipes b. Syndactyly c. Osteogenesis imperfecta d. Achondroplasia e. Scoliosis f. Ehlers-Danlos syndrome g. Marfan syndrome

7. Cardiopulmonary a. Congenital heart disease b. Cystic fibrosis c. Aortic aneurysm d. Familial idiopathic cardiomyopathy e. Idiopathic hypertrophic septal hypertrophy (subaortic stenosis)

8. Hematologic disorders a. Immunoglobulin deficiencies

b. Hemoglobinopathies (1) Sickle cell (2) Thalassemia c. Clotting disorders (1) Hemophilia (2) von Willebrand's disease (3) Hypercoagulable disorders

9. Gastrointestinal abnormalities a. Esophageal atresia b. Pyloric stenosis c. Tracheoesophageal d. Esophageal "web" e. Obesity

10. Neuromuscular disorders a. Charcot-Marie-Tooth disease b. Myotonic dystrophy c. Tourette's syndrome d. Benign familial tremor e. Muscular dystrophies

11. Neural tube defects a. Spina bifida b. Syringomyelia c. Impact of folate supplementation

12. Craniofacial abnormalities a. Cleft lip and palate b. Craniosynostosis syndromes

13. Psychiatric disorders a. Attention-deficit/hyperactivity disorder b. Schizophrenia c. Addictive personality disorder d. Bipolar affective disorder e. Associated with genetic disorders

14. Prenatal abnormalities

a. Prenatal screening (1) Alpha-fetoprotein (2) Multiple marker screening (3) Ultrasound

b. Carrier screening (1) Tay-Sachs disease (2) Canavan's disease (3) Gaucher's disease (4) Cystic fibrosis (5) Hemoglobinopathies

c. Maternal influence factors (1) Medications/drugs and chemical exposure (2) Diabetes (3) Infections

G. Approach to the dysmorphic child/adult with multiple congenital abnormalities

H. Common questions and misconceptions 1. Ionizing radiation

2. Magnetic field effects

3. The Human Genome Project

4. Multiple births (twins)

5. Cloning

6. Genetic engineering

Skills A. Preparation of a genogram/pedigree

B. Identification of local community resources for genetic counseling and consultation

C. Identification of pertinent community groups addressing the needs of patients and families with genetically based disorders

D. Basic genetic counseling for family physicians Implementation

The implementation of this curriculum component should take place during the longitudinal learning experiences throughout the 36 months of training. The curricular content should be integrated into the conference schedule and into teaching activities in the family practice center. Relevant resource and patient information materials should be available in the residency library.

Resources National Academy of Sciences. Genetic screening: programs, principles, and research. Washington, D.C.: 1975.

Gould RL. Cancer and genetics: answering your patients' questions. Huntington, N.Y.: PRR, 1997.

Doukas DJ. Primary care and the human genome project. Into the breach. Arch Fam Med 1993;2:1179-83.

Strong C. Tomorrow's prenatal genetic testing. Should we test for 'minor' diseases? Arch Fam Med 1993;2:1187-93.

Rimoin DL, Connor JM, Pyeritz RE. Emery and Rimoin's Principles and practice of medical genetics. 3d ed. New York: Churchill Livingstone, 1997.

Jorde LB, Carey JC, White RL. Medical genetics. St. Louis: Mosby, 1997.

Thompson MW, McInnes RR, Willard HF. Thompson & Thompson Genetics in medicine. 5th ed. Philadelphia: Saunders, 1991. Web Site

OMIM Home Page. Online Mendelian Inheritance in Man: www.ncbi.nlm.nih.gov/Omim/

COPYRIGHT 1999 American Academy of Family Physicians
COPYRIGHT 2000 Gale Group

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