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    Autosomal recessive: MedlinePlus Medical Encyclopedia

    Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed down through families.

    Autosomal recessive

    Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed down through families.

    An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.

    Information

    Inheriting a specific disease, condition, or trait depends on the type of chromosome that is affected. The two types are autosomal chromosomes and sex chromosomes. It also depends on whether the trait is dominant or recessive.

    A mutation in a gene on one of the first 22 nonsex chromosomes can lead to an autosomal disorder.

    Genes come in pairs. One gene in each pair comes from the mother, and the other gene comes from the father. Recessive inheritance means both genes in a pair must be abnormal to cause disease. People with only one defective gene in the pair are called carriers. These people are most often not affected with the condition. However, they can pass the abnormal gene to their children.

    CHANCES OF INHERITING A TRAIT

    If you are born to parents who both carry the same autosomal recessive gene, you have a 25% (1 in 4) chance of inheriting the abnormal gene from both parents and developing the disease. You have a 50% (1 in 2) chance of inheriting one abnormal gene. This would make you a carrier.

    In other words, for a child born to a couple who both carry the gene (but do not have signs of disease), the expected outcome for each pregnancy is:

    A 25% chance that the child is born with two normal genes (normal)

    A 50% chance that the child is born with one normal and one abnormal gene (carrier, without disease)

    A 25% chance that the child is born with two abnormal genes (at risk for the disease)

    Note: These outcomes do not mean that the children will definitely be carriers or be severely affected.

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    Definition of autosomal recessive inheritance

    A dictionary of more than 150 genetics-related terms written for healthcare professionals. This resource was developed to support the comprehensive, evidence-based, peer-reviewed PDQ cancer genetics information summaries.

    autosomal recessive inheritance

    (AW-toh-SOH-mul reh-SEH-siv in-HAYR-ih-tunts)

    One of the ways a genetic trait or a genetic condition can be inherited. In autosomal recessive inheritance, a genetic condition occurs when one variant is present on both alleles (copies) of a given gene.

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    Autosomal recessive inheritance is a way a genetic trait or condition can be passed down from parent to child. A genetic condition can occur when the child inherits one copy of a mutated (changed) gene from each parent. The parents of a child with an autosomal recessive condition usually do not have the condition. Unaffected parents are called carriers because they each carry one copy of the mutated gene and can pass it to their children.

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    Autosomal Recessive Disorders

    Autosomal Recessive Disorders

    It is an autosomal recessive disorder characterized by severely elevated concentrations of homocysteine and methionine in blood and urine.

    From: Laboratory Assessment of Vitamin Status, 2019

    Related terms:

    AllelePhosphoproteinNested GeneCystic FibrosisPhenotypeMutationAutosomal Dominant InheritanceAutosomal Recessive Inheritance

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    Genetics of Primary Immune Deficiencies

    Troy Torgerson, Hans Ochs, in Stiehm's Immune Deficiencies, 2014

    Autosomal Recessive Inheritance

    Autosomal recessive disorders occur when a person has defects in both copies of an autosomal gene (a gene that is located on any of the autosomes) (Figure 3.1B), resulting in “loss of function” (Figure 3.2A). If both copies of the gene have the same deleterious mutation, the defect is termed homozygous. If each copy of the gene has a different deleterious mutation, the defect is termed compound heterozygous. Each parent of an affected patient is typically a heterozygous carrier, and has one normal and one abnormal copy of the gene (Figure 3.1B). In most cases a normal copy of the gene can compensate for the defective copy; thus, heterozygous carriers are generally asymptomatic. When two carrier parents have offspring, statistically, one in four offspring should have the disease, two should be carriers, and one should be normal. Autosomal recessive disorders occur with increased frequency in offspring of consanguineous marriages or in isolated populations where an original “founder mutation” that occurs in one individual at some point in history is subsequently propagated throughout the population.

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    Figure 3.2. (A) Graph comparing the relative amount of protein function in a cell containing two normal copies of a gene (Wild Type) vs a cell containing two mutant copies of a gene (Loss of Function), a cell containing one normal and one mutant copy of a gene that can act in a dominant negative manner (Dominant Negative), a cell containing one normal copy of a gene that has normal function and one copy of a gene that has no function (Haploinsufficiency), and a cell containing one normal copy of a gene and one mutant copy of a gene that has a dominant gain of function (Gain of Function). (B) Mechanism of how a mutant protein with dominant negative function can decrease total protein function by more than 50% in situations where the protein multimerizes (such as forming dimers, as shown here). Protein complexes containing one mutant subunit are non-functional.

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    Basic Genetic Principles

    Fred Levine, in Fetal and Neonatal Physiology (Fifth Edition), 2017

    Autosomal Recessive Disorders

    AR disorders are those that are clinically apparent only when the patient is homozygous for the disease (i.e., both copies of the gene are mutant). The following general principles of inheritance are recognized for AR disorders (see Figure 1-7, B):

    The parents of affected children are clinically normal (i.e., carriers).

    Assuming that the carrier frequency in the population is low, only siblings are affected, and vertical transmission does not occur; the pattern therefore tends to appear horizontal.

    Consanguinity can be a factor. This can occur in outbred populations by mating between family members, or in inbred populations (e.g., the Amish) where the entire population is descended from a small number of ancestors.

    Males and females are affected in equal proportions.

    When both parents are heterozygous carriers of the mutation, 25% of their children are affected, 50% are carriers, and 25% are normal.

    Every person is a carrier of AR mutations. Fortunately, the carrier frequency for most of these mutations is so low that the likelihood that carriers will have affected children is low.

    Recessive mutations frequently involve enzymes, as opposed to regulatory and structural proteins. This is because 50% of the normal level of enzyme activity usually is sufficient for normal function. Complete enzyme deficiency produces an accumulation of one or more metabolites preceding the enzymatic block, such as the buildup of phenylalanine in phenylketonuria, and a deficiency of metabolites distal to the block. Either, or both, of these abnormalities may be responsible for the disease phenotype. Although many recessive disorders involve enzymes, two of the most common disorders with AR inheritance are cystic fibrosis, resulting from a mutation in a chloride channel, and sickle cell anemia, resulting from a mutation in the β-globin gene.

    It is important to be aware that the terms dominant and recessive refer to clinical phenotypes only. At the gene level, “dominance” and “recessiveness” do not exist. Persons heterozygous for a recessive disorder may be clinically normal, but the reduced level of functional or immunoreactive protein can be detected analytically and may lead to other biochemical abnormalities that have no obvious effect on the person's health. For example, short chain acyl-coenzyme A dehydrogenase deficiency, a disorder of short chain fatty acid metabolism, is detected by newborn screening but appears to have no clinical consequences. Patients homozygous for dominant mutations usually are more severely affected than are heterozygous patients. This is true in familial hypercholesterolemia. In many cases, the homozygous condition results in embryonic lethality, and so it is never seen clinically. Huntington disease stands out as an exception in that homozygous patients are not clinically different from heterozygous patients, presumably because the gain of function effect of the triplet repeat mutation is not dose responsive.

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