Image Based Question – 71992

Below shown is a pedigree chart.From the following given options,which of the disease would follow the inheritance pattern shown in the image?

A. Hemophilia B

B. Cystic fibrosis

C. Leber hereditary optic neuropathy

D. Marfan syndrome

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Correct Answer » B Explanation

Ans:B. Cystic Fibrosis

Autosomal Recessive inheritance pattern is shown in the image.

Determine if the pedigree chart shows an autosomal or X linked disease.

• If most of the males in the pedigree are affected, then the disorder is X-linked

• If it is a 50/50 ratio between men and women the disorder is autosomal.

Determine whether the disorder is dominant or recessive.

• If the disorder is dominant, one of the parents must have the disorder.

• If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

AUTOSOMAL RECESSIVE INHERITANCE PATTERN

• In autosomal recessive inheritance, two copies of a disease allele are required for an individual to be susceptible to expressing the phenotype.

• Typically, the parents of an affected individual are not affected but are gene carriers.

• With each pregnancy of carrier parents:

There is a one in four (25%) chance the offspring will inherit two copies of the disease allele and will therefore have the phenotype.

There is a one in two (50%) chance the offspring will inherit one copy of the disease allele and will be a carrier.

There is a one in four (25%) chance the offspring will inherit no copies of the disease allele and will not express the phenotype or be a carrier. This individual would not be at risk for passing the disorder on to his/her offspring.

• As with autosomal dominant inheritance, the proportion of affected males should be equal to the proportion of affected females in a given population.

• Autosomal recessive diseases are observed more frequently in consanguineous relationships (relationships in which the couple is related by blood, such as first cousins) because the individuals are descendants of the same ancestors and are, therefore, more likely to carry the same gene mutations.

ORGAN-BASED AUTOSOMAL RECESSIVE DISEASES

• Albinism

• α1 -Antitrypsin deficiency

• Ataxia-telangiectasia

• Autosomal recessive polycystic kidney disease

• Bernard-Soulier syndrome

• Bloom syndrome

• Chédiak-Higashi syndrome

• Crigler-Najjar syndrome type I

• Cystic fibrosis

• Dubin-Johnson syndrome

• Ehlers-Danlos syndrome (certain forms)

• Familial Mediterranean fever

• Fanconi anemia

• Friedreich ataxia

• Glanzmann thrombasthenia

• Hemochromatosis

• Kartagener syndrome

• Pseudohypoparathyroidism

• Rotor syndrome

• Severe combined immune deficiency

• Sickle cell anemia

• Thalassemia

• Wilson disease

• Xeroderma pigmentosum