Handbook of Genetic Counseling/Hemoglobinopathy Screening and Hemoglobin D-Punjab

Hemoglobinopathy Screening and Hemoglobin D-Punjab

Family History

• Some of the things I'm looking for in your family history include:
  • Birth defects
  • History of pregnancy losses
  • learning difficulties or MR
  • chronic health problems
  • anemia or blood problems
  • anyone that has difficulty breathing or fatigues easily
  • anyone who has had pregnancy losses
  • anyone who died at a young age or unexpectedly
  • Anything else that you think might be running in your family
  • Ask details about country where relatives are from because Hemoglobin D trait is more common in some ethnicities
• In Punjab region of India and Pakistan it is much more common (up to 3% of the population is has hemoglobin D trait)
• Also more common in people of English, Irish, or Scottish descent than other ethnic groups
• Estimated prevalence among American blacks is .1-.4% (Zago MA and Costa FF (1988))
  • Ask about consanguinity

Overview of Hemoglobin and genes

• Hemoglobin is the protein in blood that carries oxygen and gives blood its red color
• There are hundreds of different hemoglobin variants
  • Hemoglobin A is the usual type of hemoglobin that is made in children and adults
  • Hemoglobin D is one of the many hemoglobin variants
• The kind of hemoglobin our body makes depends on the genes we inherit
• Genes are the units of inheritance that tell our bodies how to grow and develop
• Some genes tell our bodies how to make protein chains that are essential components of hemoglobin
• One pair of genes tells the body how to make a component of hemoglobin are called beta globin genes
• Changes in these beta globin genes can alter the instructions for the cell and can result in different hemoglobinopathies
• We usually get one copy of the beta globin gene from our mother and one from our father
  • We know that ____ inherited one gene that was altered and results in the variant hemoglobin D being made and one gene that is unchanged and results in the usual hemoglobin, hemoglobin A.
  • The presence of one of the normal genes is enough to keep an individual form having any symptoms we call these people carriers

Potential Risks for future offspring

• If a person has two genes that are variants then they may have some health problems, but whether they do and the extent of problems depends on the variants they have
• One of the more common variants of the beta globin gene is one that causes sickle cell trait and sickle cell anemia due to a specific change
• Are you familiar with sickle cell disease
• Sickle cell disease only occurs if a person has two beta globin genes with the specific change present
• A person has sickle cell trait if they have one of the normal genes and one of the variant genes called S (and like those with hemoglobin D trait they do not have symptoms)
• Sickle cell trait is more common than hemoglobin D trait
• Sickle cell trait occurs in about 8% of African Americans
• Prevalence among Hispanics whose families originated from the Caribbean, Central America, or South America is approximately 4%
• Carrier rate among 2 million screened over 4 years in California showed 6,921 nonblack infants had sickle cell trait ( .35%)
• 58 out of 2 million non black children had sickle cell disease from Calif. Newborn screen
• When one partner has hemoglobin D trait and the other has sickle cell trait there is a 1 in 4 or 25% chance with each pregnancy that the child will have what is called sickle/D disease or (SD disease). (draw punnett square)
• SD disease is similar to Sickle cell Disease
• They can have severe hemolytic anemia (when they are asymptomatic the Hb D is usually a different variant)
• May have enlarged spleen, periods of severe pain called crisis, and often require blood transfusions
• They can have some of the serious life-threatening complications seen in individuals with sickle cell anemia such as increased risk of infections that will require prompt medical treatment
• (Perea F J et al. 1999) reported 4 people with SD had chronic hemolytic anemia and similar course to those with severe sickle cell anemia
• Child reported in 1984 had severe life threatening complications
• Early diagnosis and education to recognize problems and treat promptly can decrease mortality rates

Also possible to have Hb D-Punjab with other variants

• Hb D (homozygous)
• Most reports show that Hb D homozygous individuals do not have symptoms (Adekile, A D et al. (1996) and Zago, MA & Costa FF (1988).)
• Hematology is essentially normal in these individuals (Adekile AD et al. (1996)).
• Hb D and beta thalassemia trait reportedly to be even more rare than Hb D homozygotes
• Showed to not cause problems in at least 13 individuals reported worldwide as of 1999
• (Perea FJ et al. 1999) reported 3 patients with Beta thal / HbD with similar values to beta thal/ beta A heterozygote and showed microcytic and hypochromic anemia, but no harmful consequences

Testing

• Discuss ability to do simple blood test for parents to determine if they are carriers for the variants so we can clarify risks for future children (hemoglobin electrophoresis with an A2 quanitiation to identify possible beta thal)
• Covered by most insurance companies
• Some may require preauthorization so you may want to find out if this is necessary before ordering testing
• Also possible to perform this testing on future partner of _____ to determine if her children are at risk for any of the hemoglobinopathies and she may want genetic counseling when she reaches a point in her life where she is considering having a family.
• Direct mutation analysis by PCR possible (see below)

Beta Globin Variants

• Gene: ß globin
• Test: Direct mutation analysis by PCR for Hb C, E, O-Arab, D-Punjab, or other KNOWN variants as specified by the referrer.
• CPT Codes:
• (For descriptive purposes only) 83891 x1
• 83894 x2
• 83898 x1
• 83904 x2
• 83912 x1
• Sensitivity: Should be high
• Turnaround Time: Up to 3 weeks
• Cost: $200 per individual
• $600 per fetus
• Special Considerations: We require hemoglobin electrophoresis & other relevant clinical confirmation with each sample.
• This test is for molecular confirmation of a known beta globin variant. If the beta globin variant is unknown, please order the beta globin complete gene sequencing test.
• http://www.hopkinsmedicine.org/dnadiagnostic/betavariants.htm

How does the screening test determine which category a baby fits?

• Newborn screening test done in Utah since Sep 2001 measures the percentage of different types of hemoglobins using hemoglobin electrophoresis

Psychosocial concerns

• may be nervous and think there is something serious
• may be a lot of information to understand at once so talk about letter
• guilt about passing on something
• May be concerned about risks for future pregnancies

Facts about Hb D

• Hb D most common form is called Hb D-Punjab after the area in India and Pakistan where it is most frequent
• Hb D-Punjab is also referred to as Hb D-Los Angeles and by other names
• Hemoglobin D co-migrates with hemoglobin S at alkaline pH
• Hb D does not sickle
• Hb D is fourth most frequently occurring Hb variant
• Hb D results from a GAA ->CAA mutation at codon 121 glutamic acid changed to glutamine
• Quantity in heterozygote is ~40% and has been found in combination with Hb S, Hb C, Hb E, beta-thal, alpha-thal, and homozygous state

References

• Zago MA, Costa FF. Hb D-Los Angeles in Brazil: Simple Heterozygotes and Associations with B-Thalassemia dn with HB S. Hemoglobin. 12(4): 399-403. (1988)
• Perea FJ et al. Hv D-Los Angeles Associated with Hb S or B-Thalassemia in Four Mexican Mestizo Families. Hemoglobin. 23(3): 231-237. (1999).
• Kelleher JF, Park JK. Life-Threatening Complications In a Child with Hemoglobin SD-Los Angeles disease. Hemoglobin. 8(3): 203-213. (1984).
• Adekile AD et al. Co-Inheritance of Hb D-Punjab (Codon 121: GAAàCAA) and B0 -Thalassemia (IVS-II-1: GàA). Journal of Pediatric Hematology/Onclology. 18(2): 151-153. (1996).
• Newborn screening for sickle cell disease: 4 years of experience from California's newborn screening program. Journal of Pediatric Hematology Oncology. 18(1): 36-41. (1996).

Web resources

• www.urmc.rochester.edu/genetics -- great patient literature
• www.sicklecelldisease.org -- Sickle Cell Disease Association of America
• http://sickle.bwh.harvard.edu/menu_sickle.html -- basic information about hemoglobin etc.

Notes

The information in this outline was last updated in 2002.