Terminology

 

Terminology

Source: The National Human Genome Research Institute  http://www.genome.gov/glossary/index.cfm

 

 

• Allele:  one of two or more versions of a gene. An individual inherits two alleles for each gene, one from each parent. If the two alleles are the same, the individual is homozygous for that gene. If the alleles are different, the individual is heterozygous.

 

• Autosomal dominant inheritance: pattern of inheritance characteristic of some genetic diseases. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the disease-associated mutation is enough to cause the disease. Huntington’s disease is a common example of an autosomal dominant genetic disorder.

 

• Autosomal recessive inheritance: pattern of inheritance where two copies of the mutation are needed to cause the disease (one from each parent).

 

• Birth defect: (aka congenital defect) an abnormality present at birth. It can be caused by a gene mutation, an unfavorable environment during pregnancy, or a combination of both. The effect of a birth defect can be mild, severe, or incompatible with life.

 

• Candidate gene: A candidate gene is a gene whose chromosomal location is associated with a particular disease or other phenotype. Because of its location, the gene is suspected of causing the disease or other phenotype.

 

• Carrier: an individual who carries and is capable of passing on a genetic mutation associated with a disease and may or may not display disease symptoms. Carriers are associated with diseases inherited as recessive traits. In order to have the disease, an individual must have inherited mutated alleles from both parents. An individual having one normal allele and one mutated allele does not have the disease. Two carriers may produce children with the disease.

 

• Carrier Screening: type of genetic testing performed on people who display no symptoms for a genetic disorder but may be at risk for passing it on to their children. Prospective parents with a family history of a genetic disorders are candidates for carrier screening.

 

• Chromosome: an organized package of DNA found in the nucleus of the cell. Different organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes–22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosomes, X and Y. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father.

 

• Conductive hearing loss: occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear.  Conductive hearing loss usually involves a reduction in sound level or the ability to hear faint sounds. This type of hearing loss can often be corrected medically or surgically.  There are a variety of causes. (Source: http://www.asha.org/public/hearing/conductive-hearing-loss/).

 

• Congenital conditions: conditions present from birth. Birth defects are described as being congenital. They can be caused by a genetic mutation, an unfavorable environment in the uterus, or a combination of both factors.

 

• Deletion: type of mutation involving the loss of genetic material. It can be small, involving a single missing DNA base pair, or large, involving a piece of a chromosome.

 

• DNA(deoxyribonucleic acid):  chemical name for the molecule that carries genetic instructions in all living things. The DNA molecule consists of two strands that wind around one another to form a shape known as a double helix.

 

• DNA replication: the process by which a molecule of DNA is duplicated. When a cell divides, it must first duplicate its genome so that each daughter cell winds up with a complete set of chromosomes.

 

• Dominant: refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked.

 

• Enzyme: protein that speeds up the rate of a specific chemical reaction in the cell. The enzyme is not destroyed during the reaction and is used over and over. A cell contains thousands of different types of enzyme molecules, each specific to a particular chemical reaction.

 

• Family history: a record of medical information about an individual and their biological family. Human genetic data is becoming more prevalent and easy to obtain. Increasingly, this data is being used to identify individuals who are at increased risk for developing genetic disorders that run in families.

 

• Gene: the basic physical unit of inheritance. Genes are passed from parents to offspring and contain the information needed to specify traits. Genes are arranged, one after another, on structures called chromosomes. A chromosome contains a single, long DNA molecule, only a portion of which corresponds to a single gene. Humans have approximately 23,000 genes arranged on their chromosomes.

 

• Gene-environment interaction:  an influence on the expression of a trait that results from the interplay between genes and the environment. Some traits are strongly influenced by genes, while other traits are strongly influenced by the environment. Most traits, however, are influenced by one or more genes interacting in complex ways with the environment.

 

• Genetic counseling:  professional interaction between a healthcare provider with specialized knowledge of genetics and an individual or family. The genetic counselor determines whether a condition in the family may be genetic and estimates the chances that another relative may be affected. Genetic counselors also offer and interpret genetic tests that may help to estimate risk of disease. The genetic counselor conveys information in an effort to address concerns of the client and provides psychological counseling to help families adapt to their condition or risk.

 

• Genetic screening:  process of testing a population for a genetic disease in order to identify a subgroup of people that either have the disease or the potential to pass it on to their offspring.

 

• Genetic testing:  use of a laboratory test to look for genetic variations associated with a disease. The results of a genetic test can be used to confirm or rule out a suspected genetic disease or to determine the likelihood of a person passing on a mutation to their offspring. Genetic testing may be performed prenatally or after birth.

 

• Genotype:  an individual’s collection of genes. The term also can refer to the two alleles inherited for a particular gene. The genotype is expressed when the information encoded in the genes’ DNA is used to make protein and RNA molecules. The expression of the genotype contributes to the individual’s observable traits, called the phenotype.

 

• Inherited trait: genetically determined trait passed from parent to offspring 

 

• Linkage: close association of genes or other DNA sequences on the same chromosome. The closer two genes are to each other on the chromosome, the greater the probability that they will be inherited together.

 

• Locus: the specific physical location of a gene or other DNA sequence on a chromosome, like a genetic street address. The plural of locus is “loci”.

 

• Mitochondrial inheritance: mitochondrial DNA is passed from mother to all of her offspring.  Mitochondrial DNA is the small circular chromosome found inside mitochondria.  The male cannot pass on his mitochondrial DNA.

 

• Monosomy: the state of having a single copy of a chromosome pair instead of the usual two copies found in diploid cells. Monosomy can be partial if a portion of the second chromosome copy is present. Monosomy, or partial monosomy, is the cause of some human diseases such as Turner syndrome.

 

• Mosaicism: occurs when an individual has a chromosomal change that is only in some cells of the body.  The impact of the chromosomal change will depend on: the type of change, the chromosomes (and genes) affected, and the number and type of cells that contain the change.

 

• Mutation: a change in a DNA sequence. Mutations can result from DNA copying mistakes made during cell division, exposure to ionizing radiation, exposure to chemicals called mutagens, or infection by viruses. Germ line mutations occur in the eggs and sperm and can be passed on to offspring, while somatic mutations occur in body cells and are not passed on.

 

• Newborn screening:  testing performed on newborn babies to detect a wide variety of disorders. Typically, testing is performed on a blood sample obtained from a heel prick when the baby is two or three days old. In the United States, newborn screening is mandatory for several different genetic disorders, though the exact set of required tests differs from state to state.

 

• Non-syndromic disorder: a disorder that is not part of syndrome.  It is a condition with only a single, major clinical feature.  Examples of non-syndromic disorders include hearing impairment/deafness and common birth defects such as spina bifida and cleft lip with or without cleft palate.

 

• Phenotype: an individual’s observable traits, such as height, eye color, and blood type. The genetic contribution to the phenotype is called the genotype. Some traits are largely determined by the genotype, while other traits are largely determined by environmental factors.

 

• Polygenic trait: trait whose phenotype is influenced by more than one gene. Traits such as height or skin color are polygenic. Many polygenic traits are also influenced by the environment and are called multifactorial.

 

• Proteins: important class of molecules found in all living cells. A protein is composed of one or more long chains of amino acids.  Proteins play a variety of roles in the cell, including structural (cytoskeleton), mechanical (muscle), biochemical (enzymes), and cell signaling (hormones).

 

• Recessive: quality found in the relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent. If the alleles are different, the dominant allele will be expressed, while the effect of the other allele, called recessive, is masked. In the case of a recessive genetic disorder, an individual must inherit two copies of the mutated allele in order for the disease to be present.

 

• Risk:  in the context of genetics, refers to the probability that an individual will be affected by a particular genetic disorder. Both genes and environment influence risk. An individual’s risk may be higher because they inherit genes that cause susceptibility to a disorder. Other individuals may be at higher risk because they live/work in an environment that promotes the development of the disorder.

 

• Sensorineural hearing loss (SNHL): occurs when there is damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain. Most of the time, SNHL cannot be medically or surgically corrected.  This is the most common type of permanent hearing loss. 

SNHL reduces the ability to hear faint sounds. Even when speech is loud enough to hear, it may still be unclear or sound muffled. (Source: http://www.asha.org/public/hearing/sensorineural-hearing-loss/)

 

• Sex chromosome:  type of chromosome that participates in sex determination. Humans have two sex chromosomes, the X and the Y. Females have two X chromosomes in their cells, while males have both X and a Y chromosomes in their cells. Egg cells all contain an X chromosome, while sperm cells contain an X or Y chromosome.

 

• Susceptibility:  condition of the body that increases the likelihood that the individual will develop a particular disease. Susceptibility is influenced by a combination of genetic and environmental factors.

 

• Syndrome/syndromic disorder: a collection of recognizable traits or abnormalities that occur together and are associated with a specific disease.

 

• Translocation: type of chromosomal abnormality in which a chromosome breaks and a portion of it reattaches to a different chromosome.

 

• X-linked inheritance: X-linked genes are located on the X chromosome.  In an X-linked or sex linked disease, it is usually males that are affected because they have a single copy of the X chromosome that carries the mutation. In females, the effect of the mutation may be masked by the second healthy copy of the X chromosome.

 

Additional Resources

 

• Speech and Language Terms and Abbreviations
• http://www.oafccd.com/factshee/fact59.htm

 

• Incidence and Prevalence of Communication Disorders and Hearing Loss in Children – 2008 Edition
• http://www.asha.org/Research/reports/children/

 

• Deafness and Hereditary Hearing Loss Overview
• http://www.ncbi.nlm.nih.gov/books/NBK1434/

 

Mental Illnesses

 Mental illness:

Schizophrenia is one mental illness that has a genetic component. There is a wide variety of symptoms and not all people diagnosed with Schizophrenia always exhibit all the symptoms. These symptoms usually first appear in late adolescence or early adult life.  Symptoms always include a psychotic episode that include: losing touch with reality, hallucinations, delusions, and paranoia. They may also include disorganization of thoughts and feelings and social withdrawal. Schizophrenia symptoms usually develop slowly over months or years. Sometimes you may have many symptoms, and at other times you may only have a few. Schizophrenia is a chronic, severe, and disabling brain disorder that affects about 1.1 percent of the U.S. population age 18 and older in a given year. A person with Schizophrenia may find it difficult to: tell the difference between real and unreal experiences, think logically, have normal emotional responses and behave normally in social situations. With medication, therapy, and support, many people with schizophrenia are able to control their symptoms, gain greater independence, and lead fulfilling lives. It is likely that several different genes are involved, perhaps causing susceptibility to different forms of schizophrenia. In some families, there may be genes that have a major effect on the risk of development of schizophrenia. It appears that there is also an increased risk for having a child affected by schizophrenia at some time in your life if the father was over 50 years of age when the child was born.

 

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001925/

 

http://helpguide.org/mental/schizophrenia_symptom.htm

Bipolar Disorder

  Bipolar disorder is another mental illness that has a genetic component. Bipolar disorder is a disorder of mood and is characterized by major mood swings. A person with the condition will experience periods of intense activity, termed mania, and other periods of feelings of hopelessness termed depression.  The mood swings appear to occur spontaneously, without any obvious external cause. The pattern of ‘highs’ and ‘lows’ can occur repeatedly with little or no breaks between each episode or may occur periodically between long periods when the person shows no symptoms. About 5.7 million U.S. adults are living with bipolar disorder. Bipolar disorder affects men and women equally, as well as all races, ethnic groups, and socioeconomic classes. Several genes have also been identified that play a role on people having bipolar disorder. For example, a specific gene that plays a role in the brain. People with a change in this gene appear to be at twice the risk of developing bipolar disorder, though it is not yet clear exactly why.

 

http://helpguide.org/topics/bipolar.htm

 

http://www.webmd.com/bipolar-disorder/guide/bipolar-disorder-overview-facts\

 

http://www.youtube.com/watch?v=WzNwLvsA87E

 

http://mentalhealth.gov/health/publications/bipolar-disorder/complete-index.shtml

Fragile X Syndrome

Fragile X syndrome is the most common form of inherited mental retardation. A problem with a specific gene causes the disease. Normally, the gene makes a protein you need for brain development, Fragile X Mental Retardation 1 (FMR1) gene.  But when there is a change in this gene, the body makes only a little bit or none of the protein, which can cause the symptoms of Fragile X.

 

Many males with fragile X syndrome have characteristic physical features that become more apparent with age. These features include a long and narrow face, large ears, prominent jaw and forehead, unusually flexible fingers, and enlarged testicles (macroorchidism) after puberty.

 

People with only a small change in the gene might not show any signs of Fragile X. People with bigger changes can have severe symptoms. These might include

—  Intelligence problems, ranging from learning disabilities to severe mental retardation

—  Social and emotional problems, such as aggression in boys or shyness in girls

—  Speech and language problems, especially in boys

 

 

 

Fragile X has no cure. You can treat some symptoms with educational, behavioral or physical therapy, and with medicines.

 

Males and females with fragile X syndrome may have anxiety and hyperactive behavior such as fidgeting, excessive physical movements, or impulsive actions. They may also have attention deficit disorder, which includes an impaired ability to maintain attention and difficulty focusing on specific tasks. About one-third of males with fragile X syndrome also have autism or autistic-like behavior that affects communication and social interaction. Seizures occur in about 15 percent of males and about 5 percent of females with fragile X syndrome.

 

 

Fragile X syndrome occurs in approximately 1 in 4,000 males and 1 in 8,000 females.

 

Websites:

 

Fragile X Syndrome

http://www.asha.org/Publications/leader/2003/031021/f031021b.htm

 

Fragile X Syndrome

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002633/

 

 

 

Autism

Autism:

(A complex developmental brain disorder known as Pervasive Developmental Disorders (PDD), Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS), or Asperger Syndrome.  Autism affects 1 in every 110 births in the United States, and almost 1 in 70 boys (Autism Society).

Characteristics of Autism

• Impairments in communication
• Impairments in social interactions
• Repetitive behaviors
• Lifelong
• Non-progressive
• Males are 4 times more likely to be affected

Genetic or Not?

• In about 90% cases of Autism, the cause is unknown.
• There is no conclusive evidence of Autism being related to vaccines, mother’s illness in pregnancy, the child’s diet early in life
• There is however evidence that genetics play a role in Autism development.  For example, it is more likely for identical twins to have Autism.  Also, there is sibling recurrence for Autism.  For example:

 

* Figure based on data from “The UCLA-University of Utah epidemiologic survey of autism: recurrence risk estimates and genetic counseling” Am J Psychiatry 1989; 146:1032-1036

—  Because more males have Autism compared to females, there is a suggestion that the genes that cause Autism may lie on the X chromosome.

—  Also because there is a large variability of symptoms within individuals with Autism, there may be many faulty genes that cause the severity of autistic behaviors.

—  Researches have identified a number of genes that are associated with the disorder as well as irregularities in regions of the brain.  Some studies also show that individuals with Autism have abnormal levels of serotonin or other neurotransmitters in the brain. 

—  This is ALL still being researched.

For additional resources, visit:

• http://www.autismspeaks.org/
• http://www.autism-society.org/
• http://www.ninds.nih.gov/disorders/autism/detail_autism.htm#189053082
• http://www.nimh.nih.gov/health/topics/autism-spectrum-disorders-pervasive-developmental-disorders/nih-initiatives/nih-autism-coordinating-committee.shtml
• http://www.genetics.edu.au/pdf/factsheets/fs43.pdf

Down Syndrom (Trisomy 21)

Down Syndrome (Trisomy 21):

A chromosomal abnormality.  Trisomy 21 is the most common, affecting 95% of individuals.  Down Syndrome affects 13.7 individuals per 10,000 births.  It is the single most common cause of human birth defects.

 

Characteristics of Down Syndrome

• Physical characteristics such as a three-palm print pattern, brushfield spots (colored specks in the iris of the eye), ear length, neck skinfold, short stature (to name a few).
• Increased risk of congenital heart defects
• Higher chance of Alzheimer’s disease because of tangles in the brain
• Sensory impairments (vision and hearing particularly)
• Higher chance of developing diabetes
• Dental problems
• Gross motor progress is typically slow
• Late to develop speech

How Genes affect individuals

• Trisomy 21/Down Syndrome occurs when there is an extra copy of chromosome 21.  So they carry 47 chromosomes, rather than the normal 46.
• Maternal age is linked to the prevalence (as the mother is older, the risk increases).
• Mother can undergo prenatal diagnostic testing through blood screening tests and fetal ultrasounds

 

For additional resources, visit:

• http://www.trianglemom2mom.com/special-needs-support#downsyndrome
• http://triangledownsyndrome.org/cmsmadesimple/index.php
• http://www.ndss.org
• http://www.arcwake.org/kidconnect.html
• http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001992/
• http://www.ds-health.com/trisomy.htm

 

Speech-Language, Reading, and Writing Delays

Speech-Language, Reading, & Writing Delays

 Research has shown that communication skills are strongly tied to genetic factors.  The information stored in chromosomes (genes) has been linked todevelopment of numerous communication skills, including speech-sound production, syntax, semantics, spelling, speed of processing, reading abilities, oral-motor skills, and verbal memory.   These skills and abilities are determined by the interaction of numerous genes as well as the child’senvironment.  In some cases, a single genetic defect may cause multiple developmental problems.  In other cases, there may be several faulty genes involved, which may lead to disorders or delays in speech, language, and reading.  Most of the time, more than one gene is to blame for developmental deficits or disorders.  Complicating matters even further, multiple risk genes may act together or alone to cause different profiles of skills or impairment that fall under the same general diagnosis.

Dyslexia (also known as Developmental reading disorder, or DRD) is an example of a genetically linked disorder that can be passed through families. DRD is characterized by deficits “in areas of the brain that help interpret language” (U.S. National Library of Medicine, http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002379/).

In children with dyslexia, deficits are not limited to just reading, the areas of speech-sound production, writing, and math can also be affected.  There is a very strong chance that parents affected by dyslexia will pass the disorder on to their children.  Studies have shown strong connections between dyslexia and several different genes located on particular chromosomes.  This may mean that there are different types of dyslexia, or multiple ways to inherit the disorder.

Other Helpful Resources:

 

Speech and Language Impairments and Related Disorders

http://www.childspeech.net/u_v.html

Causes of Learning Disabilities and Dyslexia

http://web4health.info/it/child-learn-biology.htm

Information for parents about dyslexia:

http://dyslexia.yale.edu/parents.html

Information about the connection between genetics and speech/language disorders and the KE Family:

http://brainconnection.positscience.com/topics/?main=sci-news/language-speech

The Role of Genetics in Speech, Language, and Reading Disorders among Children

http://www.case.edu/artsci/cosi/fsrs/documents/lewis_brief_final.pdf

Hearing Impairment

Hearing Impairment

 

Severe-to-profound sensorineural hearing impairment (or deafness) is a common congenital birth defect or childhood disorder.  Children with congenital hearing impairment that is severe-to-profound require hearing aids or some other type of amplification system in order to develop speech and language.  Approximately 1 in every 1,000 children is affected by severe-to-profound congenital hearing loss.  About 50% of these cases are due to genetic causes.

 

Severe-to-profound congenital sensorineural hearing impairment can occur alone, or as part of a collection of symptoms that makes up a syndrome.  In most cases (approximately 70%), congenital hearing impairment occurs as a non-syndromic disorder.  In other words, hearing impairment typically occurs without any other significant symptoms or conditions.  However, severe-to-profound congenital hearing impairment has also been identified as a symptom of over 400 syndromes, many of which are very rare (such as Waardenburg syndrome and Turner Syndrome).  In about 30% of cases, hearing impairment occurs as part of a syndrome.

 

Severe-to-profound congenital sensorineural hearing loss has been linked to numerous different genes.  Some experts have suggested that hearing impairment is linked to over 100 genes.  This type of hearing impairment is most commonly inherited according to an autosomal recessive pattern.  Approximately 77% of cases of genetically linked hearing impairment are inherited according to this pattern.  This means that the child must receive a copy of the faulty recessive gene from each parent.  Generally, children affected by this type of hearing loss have unaffected (normal-hearing) parents. In other words, both parents are carriers for the disorder.  The second most common type of inheritance for severe-to-profound congenital hearing loss, occurring in approximately 22% of cases is autosomal dominant.  In these cases, the child needs only one copy of the faulty gene (from one parent) to inherit the disorder.

Genetics and Speech-Language therapy

How does genetics and DNA tie in with Speech-Language therapy?

• Speech-Language Pathologists are often the first to suspect that their clients have a genetic disorder, give a label to the symptoms, and recommend further evaluations, including genetic testing
• Speech, language, and hearing disorders are increasingly linked to genetic causes

 

 

Genetic Screening,Testing,and Counseling

Newborn Screening involves testing of all newborn babies to detect a wide variety of disorders that are not apparent at birth.  Typically, testing is “performed on a blood sample obtained from a heel prick when the baby is two or three days old. In the United States, newborn screening is mandatory for several different genetic disorders, though the exact set of required tests differs from state to state” (Source: The National Human Genome Research Institute  http://www.genome.gov/glossary/index.cfm). 

 Newborn screenings test for disease including Sickle Cell Disease, žBiotinidase Deficiency, Congenital Adrenal Hyperplasia, Maple Syrup Urine Disease (MSUD), Cystic Fibrosis, žToxoplasmosis, and hearing impairment. For some disorders, early diagnosis and treatment could mean the difference between lifelong impairment and healthy development.

For more information about newborn screenings, visit: http://www.babyhearing.org/HearingAmplification/NewbornScreening/index.asp

http://kidshealth.org/parent/system/medical/newborn_screening_tests.html

http://abcnews.go.com/WNT/video/genetic-screenings-make-healthy-babies-9722033

 

 Genetic Screening for a particular condition in individuals, groups or populations is performed when there is no family history of the condition.  It is “the process of testing a population for a genetic disease in order to identify a subgroup of people that either have the disease or the potential to pass it on to their offspring” (The National Human Genome Research Institute http://www.genome.gov/glossary/index.cfm).   

Genetic screening involves testing of blood and other body tissues for particular conditions.  It can be performed on people of all ages, and follows the model of newborn screening, identifying both affected individuals and carriers.  Goals of genetic screening include:

• žcontributing to improvement in the health of persons who suffer from genetic disorders; and/or
• žallowing carriers for a given abnormal gene to make informed choices regarding reproduction; and/or
• žhelping to alleviate the anxieties of families and communities faced with the prospect of serious genetic disease

 

 

Genetic testing is available for those who are at-risk due to a family history of inherited disorders, individuals suspected of having a genetic condition, and those who have failed genetic screenings.  It involves the “use of a laboratory test to look for genetic variations associated with a disease. The results of a genetic test can be used to confirm or rule out a suspected genetic disease or to determine the likelihood of a person passing on a mutation to their offspring. Genetic testing may be performed prenatally or after birth.” (The National Human Genome Research Institute http://www.genome.gov/glossary/index.cfm).

In genetic testing, blood and other tissues are tested to find possible genetic diseases in unborn babies, identify carriers for particular genes or disorders, screen embryos for disease, and identify genetic disorders in adults before the onset of symptoms.  Additionally, genetic testing can be used to confirm a diagnosis of a genetic disorder.  Results of genetic testing may help a person make life decisions, such as career choice, family planning or insurance coverage.

 

For more information about genetic testing, visit:

http://www.genetics.edu.au/pdf/factsheets/fs21.pdf

http://hearing.harvard.edu/info/Ins1_Facts.pdf

 

Genetic counseling involves “professional interaction between a healthcare provider with specialized knowledge of genetics and an individual or family. The genetic counselor determines whether a condition in the family may be genetic and estimates the chances that another relative may be affected. Genetic counselors also offer and interpret genetic tests that may help to estimate risk of disease. The genetic counselor conveys information in an effort to address concerns of the client and provides psychological counseling to help families adapt to their condition or risk” (The National Human Genome Research Institute http://www.genome.gov/glossary/index.cfm).

 

 

 

 

 

 

For more information on genetic counseling, visit: http://kidshealth.org/parent/medical/genetic/genetic_counseling.html

http://www.nlm.nih.gov/medlineplus/geneticcounseling.html

http://www.youtube.com/watch?v=dJuo937gz44

 

 

Dominant and recessive inheritance

Dominant and recessive inheritance

Inheritance of a specific disease, condition, or trait depends on the type of chromosome affected (autosomal or sex chromosome). It also depends on whether the trait is dominant or recessive. Sex-linked diseases are inherited through one of the sex chromosomes (the X or Y chromosome).

Dominant inheritance occurs when an abnormal gene from one parent is capable of causing disease, even though a matching gene from the other parent is normal. The abnormal gene dominates the gene pair. (source:http://www.nlm.nih.gov/medlineplus/ency/article/002050.htm)

Autosomal dominant: If some family members in each generation are affected, and others are unaffected, then the disease is probably autosomal dominant. Both males and females are equally likely to be affected, and an affected offspring usually has an affected parent.

Autosomal recessive: The disorder is autosomal recessive if only individuals who have two copies of the abnormal gene exhibit the disorder. Those who have one normal and one abnormal copy are not affected and are called “carriers.” It is important to remember that the disorder may not be present in every generation. Also, parents of the affected individuals may not have the disorder.

X-linked recessive: If all the family members with the disorder are males, and none of the affected fathers have affected sons, then the hearing loss is probably X-linked recessive. This is because males have only one X chromosome and they inherit it from their mother. If the mother is a carrier, each son has a 50% chance of inheriting the abnormal copy of the X-linked gene and having the disorder. (Note that all daughters of affected fathers will be carriers because they all inherit their father’s X chromosome.)

 

 

Hallmarks of X-linked recessive inheritance

• With any X-linked trait, the disease is never passed from father to son.
• Males are much more likely to be affected than females. If affected males cannot reproduce, only males will be affected.
• All affected males in a family are related through their mothers.
• Trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons.

 

X-linked dominant- For an X-linked dominant disorder: If the father carries the abnormal X gene, all of his daughters will inherit the disease and none of his sons will have the disease. If the mother carries the abnormal X gene, half of all their children (daughters and sons) will inherit the disease tendency.

Mitochondrial– the mother passes the trait on to all of her children, however it stops (or the affected male) does not pass it on.

 

 

Websites:

United Mitochondrial Disease Foundation

http://www.umdf.org/site/c.otJVJ7MMIqE/b.5692899/

 

Children’s Hospital of Winsconsin

http://www.chw.org/display/PPF/DocID/22920/router.asp