Human genetics

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Human genetics became a predominant field of late 20th-century science once techniques in molecular biology were applied to pedigree studies in families with recurring cases of inherited diseases. With the sequencing of the human genome in the 21st century, genomics is predicted to have a place in routine aspects of medical care. As a sub-specialty within medicine, the clinical practice of human genetics had already been established in many countries of the world before molecular genetic tests were available to confirm diagnoses of genetic diseases, and even before DNA had been discovered. The first human geneticists were physicians who specialized in treating patients with inherited abnormalities of metabolism, the so-called metabolic diseases. Diagnosed in the early 20th century as inborn biochemical abnormalities in human metabolism that followed a Mendalian pattern of inheritance, the very first of these (alkaptonuria) was identified in 1902 by the physician, Archibald E Garrod. Clinical geneticists practiced with a focus on these rare diseases that are the result of single gene alleles that interfere with normal biochemical pathways in cells, but, starting primarily in the post WW II era, also treated chromosomal abnormalities, and genetic patterns for infertilty or repeated miscarriages in families. The specialty of human genetics therefore significantly predates the discovery of DNA in 1953. By the 1970's when cytogenetic examination of cells from the fetus and placenta collected during pregnancy by amniocentesis allowed prenatal diagnosis of chromosomal disorders like Down syndrome to be made, clinical geneticists began to have a role in routine obstetrical care of older women as well as couples with family histories of inherited disease. This role has been expanded in the wake of molecular genetic tests for single gene defects. As the human genome has been sequenced, and more alleles have been identified that play a role in human health and disease, general medicine and internal medicine, as well as other medical specialties, have begun to include genomics as part of practice, but the numbers of board-certified or eligible physicians specializing in human genetics has not increased.(reference:Korf BR, Feldman G, Wiesner GL. Report of Banbury Summit meeting on training of physicians in medical genetics, October 20–22, 2004. Genet Med 2005;7:433–438.) Instead, human geneticists are playing a primary role in maintaining quality in ever expanding clinical laboratories that offer tests for genetic diseases, and in supervising the care of individuals with rare and severe disorders and syndromes that are either known to have a genetic basis or require an answer to the question of whether or not there is a genetic basis to the disease.

Development of human genetics as a field in medicine and clinical laboratory science

In the USA, "MD clinical geneticists comprise the primary medical specialist group trained and certified in clinical genetics, although their numbers are small when compared with other medical specialties. In 2005, there were only 1,178 board-certified MD clinical geneticists among the more than 697,000 board-certified physicians."(reference:Cooksey JA. Forte G. Flanagan PA. Benkendorf J. Blitzer MG. The medical genetics workforce: an analysis of clinical geneticist subgroups. [Journal Article. Genetics in Medicine. 8(10):603-14, 2006 Oct. UI: 17079876

In Britain, the practice of clinical geneticists is supported by the National health Service in regional genetic centres in 12 UK health regionsl. (Donnai D. Elles R. Integrated regional genetic services: current and future provision. BMJ. 322(7293):1048-52, 2001 Apr 28. UI: 11325774 )

Educational, training, and certification requirements

(ref:Korf BR, Feldman G, Wiesner GL. Report of Banbury Summit meeting on training of physicians in medical genetics, October 20–22, 2004. Genet Med 2005;7:433–438.)

Ethics and professional conduct

Genetic evaluation of families has certain ethical problems that routinely arise. In order to evaluate the chances that a particular individual does or does not have a genetic disease, tests of relatives are ordinarily required, or at least are optimal. In Britain, "the Joint Committee on Medical Genetics set up a working party to review current clinical practice and to offer guidance and has just published its report, Consent and confidentiality in genetic practice: guidance on genetic testing and sharing genetic information."(Farndon PA. Joint Committee on Medical Genetics. Recording, using and sharing genetic information and test results: consent is the key in all medical specialties. Clinical Medicine. 6(3):236-8, 2006 May-Jun. UI: 16826852).

Important leaders in the history of human genetics

  • James V. Neel
  • Penrose (PKU, Down syndrome)

Patients and clients seen by physician geneticists

In the United States, recent surveys have shown that about 70% of the patients seen by physicians specializing in genetics are children, their clients include, of course, the paremnts of those children. Almost half of the children seen in practice are newborns or infants, and these are primarily brought to the attention of the physician because of birth defects, including metabolic defects, physical deformities, chromosomal abnormalities and other syndromes. Toddlers, older children and adolescents make up the slight majority of pediatric patients, and include similar diagnoses and presenting problems, along with those children being evaluated for developmental delay.

At this time, about 30% of patients seen by physicians specializing in human genetics are adults, and they are most often evaluated as a part of assisted reproduction care or in an evaluation for infertility, or as ongoing care of a metabolic defect, or in consultation for a single-gene adult onset disease such as certain types of cancer or other diseases such as Huntingtons disease (Huntingtons chorea).

In Britain, the following conditions, or question of such a condition, are the most common reason patients undergo molecular genetic tests:

  • Fragile X syndrome
  • Cystic fibrosis
  • Factor V Leiden deficiency
  • Breast or ovarian cancer
  • Haemochromatosis
  • Prader Willi or Angelman syndromes
  • Myotonic dystrophy
  • Huntington's disease
  • Duchenne's or Becker's muscular dystrophy
  • Charcot-Marie tooth disease

Commonest indications for cytogenetic tests

  • Birth defects
  • Learning difficulties
  • Prenatal diagnosis
  • Reproductive problems
  • Malignancy

(from:Donnai D. Elles R. Integrated regional genetic services: current and future provision. BMJ. 322(7293):1048-52, 2001 Apr 28. UI: 11325774)

Geneticists' role in reproduction health services


Cooksey JA. Forte G. Benkendorf J. Blitzer MG. The state of the medical geneticist workforce: findings of the 2003 survey of American Board of Medical Genetics certified geneticists. Genetics in Medicine. 7(6):439-43, 2005 Jul-Aug. UI: 1602497)

Valle D. Harland Sanders Award Statement. Genetics in Medicine. 1(5):219-23, 1999 Jul-Aug. UI: 11256676 (Barton Childs- anoaous genes not "things apart)

Further reading

External links

American Board of Human Genetics