How disabilities come to be

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How disabilities come to be

• Causes, roots, and beginnings

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Reason 1. Its Genetic!

• DNA (deoxyribonucleic acid) is a nucleic acid
  that is
• the most basic unit of genetic information.
• Chromosomes are highly organized structures
• containing DNA in long strands. Most cells in our
  body
• (except for mature red blood cells) contain a
  complete
• set of 46 chromosomes, or 23 pairs.

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Chromosomes, etc.
lt Agt

• The chromosomes are numbered 1-22
• (largest to smallest) and the 23rd pair are
• the sex chromosomes, which determine
• our gender (two "X" chromosomes
• female one "X" and one "Y" chromosome
• male). We inherit our chromosomes at
• the time of conception one set of 23
• from our mother and one set of 23 from
• our father. As we grow from a single cell
• into a complex human being, our
• chromosomes are copied into each new
• cell.

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Genes

• Genes are specific subunits or groups of DNA
  along the
• chromosomes. Just as our chromosomes come in
  pairs,
• so do our genes. Each gene codes for a protein
  (or
• chemical) that has a specific function in the
  body.

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Meiosis

• Meiosis the
• formation of
• ova and sperm. During
• In this process,
• chromosomal
• mutations may
• occur.

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Reason 1a. Autosomal dominant inheritance.

• Autosomal dominant conditions affect males
• and females equally, and only one gene of the
• pair needs to be abnormal for the individual to
• have the condition. Every child of an individual
• with an autosomal dominant condition has a 50
• chance of inheriting the mutation and having the
• disorder.

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Autosomal dominant

• If the AD gene is
• there, it is expressed.
• No carriers here.
• Children have a
• 50/50 chance of also
• being affected by the
• disorder (one parent
• affected).

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BOTH parents have dominant gene

• Statistically, there is a 25 chance that the
  child will inherit the two unaffected genes and
  will be unaffected.
• There is a 50 chance that the child will inherit
  at least one affected gene, and will have the
  disorder.
• There is a 25 chance that the child will inherit
  both dominant genes, which is usually fatal.

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Examples of AD

• Neurofibromatosis
• Tuberous Sclerosis
• Marfan Syndrome
• Achondroplasia
• Osteogenesis Imperfecta (there are 7 distinct
  types Type II is NM)
• Noonan syndrome
• Cornelia de Lange syndrome
• Apert syndrome
• Treacher-Collins syndrome
• Aniridia
• new mutations originally AD inheritance when
  passed from an affected individual.

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Reason 1b. Autosomal recessive inheritance.

• Autosomal recessive conditions affect males and
  females
• equally, but both copies of the recessive gene
  have to be present
• for the individual to have the condition.
  Autosomal recessive
• conditions can be passed on when each parent is a
  "carrier" for
• the condition, and their offspring have a 25
  risk of inheriting the
• condition. "Carriers" have one abnormal copy of
  the gene but do
• not have clinical symptoms and are not at
  increased risk to
• develop the condition. A family history of a
  recessive condition
• can reveal multiple individuals in a single
  generation (brothers and
• sisters) with the condition in the case of small
  families, however,
• there may be only one affected individual.

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Autosomal recessive

• Two carrier parents,
• statistically 1
• unaffected, 2
• carriers, and one
• affected. (25
• chance of being
• affected by the
• recessive gene)

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Autosomal recessive one carrier parent

• As indicated, if only ONE parent is a carrier
• of a recessive trait, then there is no chance
• for one of the
• children to be
• affected
• however, a
• 50 chance of
• being a carrier.

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Autosomal recessive one affected parent one
non-carrier

• All children will be
• carriers, since they
• must inherit one
• affected (recessive)
• gene from the
• affected parent, but
• one (dominant)
• gene from the
• unaffected parent.

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Autosomal recessive one affected parent one
carrier parent

• With the carrier parent, the statistics change to
  a 50 chance of being affected 50 chance of
  being a carrier.

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Examples of AR

• Usher syndrome
• Retinitis pigmentosa (AR in 20 to 25 of cases
  AD in 15 -- 20 XLR in 10 -- 15)
• Tay-Sachs disease
• Sickle Cell Anemia
• Phenylketonuria
• Batten disease
• Pendred syndrome
• Spinal Muscular Atrophy
• Albinism
• Torsion Dystonia (or AD)

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Reason 1c. X-Linked Recessive Inheritance

• Most X-linked conditions occur in males who
• inherit an abnormal copy of the gene from their
• mothers. Since males only have one X
• chromosome, if it carries an abnormal copy of the
  
• gene, they will suffer from the disorder. These
• mothers carry a copy of the altered gene but are
• usually unaffected if their other X chromosome
• has a normal working copy of the gene.

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X-Linked Recessive

• An affected male never
• transmits the disease to his
• sons since the X chromosome
• is always passed on from
• mother to son. When the
• mother carries a copy of a
• gene for an X-linked disease,
• the chance of inheriting the
• altered gene is 1 in 2 in each
• pregnancy for both boys and
• girls, but only the male
• offspring will be affected.

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X-linked recessive affected father

• In this family, the
• father is affected by
• an X-linked
• (recessive) disorder.
• The sons inherit the
• Y chromosome from
• their father. All
• daughters inherit a
• recessive gene, i.e.,
• are healthy carriers.

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X-linked recessive carrier mother affected
father

• If the mother is a carrier (XXa) and the father
  is affected (XaY), the children will
  statistically be (girls 50 carrier, 50
  affected boys 50 unaffected 50 affected)
• Mother X Xa
• Father Xa
• Y

XXa (carrier girl)
XaXa (affected girl)
XY (unaffected boy)
XaY (affected boy)
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X-linked recessive affected mother (XaXa) and
father (XaY)

• Mother and father are affected by the X-linked
  recessive gene all children are affected by the
  recessive gene.
• Mother Xa Xa
• Father Xa
• Y

XaXa (affected girl)
XaXa (affected girl)
XaY (affected boy)
XaY (affected boy)
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Examples of XLR

• Color Blindness
• Hemophilia
• Fragile X Syndrome
• Duchenne Muscular Dystrophy
• Spinal Bulbar Muscular atrophy
• Norrie Disease
• Menkes syndrome

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Reason 1d X-linked Dominant Inheritance

• When an X-linked gene is said to express dominant
  inheritance, it means that a
• single dose of the mutant allele will affect the
  phenotype of the female. A
• recessive X-linked gene requires two doses of the
  mutant allele to affect the
• female phenotype. The following are the hallmarks
  of X-linked dominant
• inheritance
• The trait is never passed from father to son.
• All daughters of an affected male and a normal
  female are affected. All sons of an affected male
  and a normal female are normal.
• Matings of affected females and normal males
  produce 1/2 the sons affected and 1/2 the
  daughters affected.
• Males are usually more severely affected than
  females. The trait may be
• lethal in males.
• In the general population, females are more
  likely to be affected than males,
• even if the disease is not lethal in males.

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X-linked dominant

• Offspring of either gender
• have a 50/50 chance of
• inheriting XLD, if the
• mother is affected. If the
• father is affected, the
• boys will not be affected,
• but girls will always.

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Examples of XLD

• Aicardi syndrome (occasional new mutation)
• Charcot-Marie Tooth Disease (type X)
• Hypophosphatemic rickets
• Rett syndrome

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Reason 1e Sporadic or new mutations

• A MUTATION is a sudden, permanent
• change in DNA.
• This change has the potential to cause
• disorders or diseases.
• A sporadic or new mutation of this sort
• has no real risk for recurrence, as a
• general rule, and remember rules are
• always broken.

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Examples of Sporadic/New mutation

• Trisomy 13 (Patau syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 21 (Down syndrome)
• Cri-du-chat syndrome
• Prader-Willi syndrome
• Rubenstein-Taybi syndrome

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Here are some syndromes that belong in this
category but could be considered in the X-linked.
But they go here, OK?

• XXY syndrome (Klinefelter syndrome)
• XXX syndrome
• Turner syndrome (XO)
• XYY syndrome
• And other disorders involving multiple Xs or Ys.

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Reason 2 Multifactorial

• Many reasons exist that might actually
• cause these disorders some genetic,
• some environmental, some because of
• the interplay between the genes and
• environment. So all of those disorders go
• HERE.

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Examples of multifactorial

• Spina Bifida
• Cancer
• Cleft palate
• Osteoporosis
• Meningitis
• Congenital heart defects
• Encephalitis
• Anencephaly
• Microcephaly
• Pyloric Stenosis
• Hydrocephaly

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Reason 3 Perinatal incidents

• Conditions, complications, incidents, accidents,
  mistakes, the unfolding of unfortunate events
  that occur before, during, or immediately
  following childbirth.

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Examples of Perinatal

• Jaundice
• Cerebral palsy
• Prematurity
• Respiratory distress syndrome
• Failure to thrive (maybe )
• Anoxia

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Reason 4a Teratogens

• Agents that cause malformations in a developing
  embryo. These agents cross the placental barrier
  and cause or increase the incidence of physical
  malformations and behavioral and cognitive
  deficits. Examples are any medication, chemical,
  infectious disease, or environmental agent that
  might interfere with the normal development of a
  fetus result in the loss of a pregnancy, a birth
  defect, or a pregnancy complication.

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Examples of teratogens

• Toxoplasmosis
• Fetal Alcohol Syndrome
• Cocaine-exposed or addicted

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Reason 4b Maternal conditions

• Infections, diseases, or disorders of a mother
  during pregnancy, sometimes having the potential
  to injure the unborn child.

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Examples of Maternal condition

• AIDS
• HIV
• Herpes
• Congenital rubella syndrome
• Cytomegalovirus

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Reason 5 Abuse

• The physical or mental injury, sexual abuse, or
  negligent
• treatment of a child under the age of 18 by a
  person who is
• responsible for the child's welfare. The specific
  types are physical
• abuse, physical neglect, emotional abuse,
  emotional neglect,
• sexual abuse, sexual exploitation,
• physical endangerment,
• abandonment, medical and
• psychological neglect,
• educational neglect, and
• improper ethical guidance.

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Examples of Abuse

• Shaken Baby Syndrome
• Nonorganic Failure to Thrive

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REASON 6 Accident, Injury, Illness

• Many disabilities with
• long-term consequences
• are caused by accidents
• or illness. Some
• disabilities are directly the
• result of the accident or
• illness others as a
• secondary condition.

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Reason 7 Unknown

• No idea. Well, maybe an idea, but nothing has
  panned out so far. But still looking. Well let
  you know.

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Examples of UNKNOWN

• Autism
• Amblyopia
• Sudden Infant Death Syndrome
• Asperger Syndrome
• Dyslexia
• ADHD
• Epilepsy
• Scoliosis
• Celiac Disease