Honors Biology Final Project

Some Common Genetic Disorders That Affect Human

Body Systems

The Human Genome is made of DNA

The human genome is a book.

This book has 23 chapters, called chromosomes.

Each chapter contains several thousand stories, called genes.

Each paragraph is made up of words, called codons.

Each word is written in letters, called bases.

Changes in the Stories are Mutations We inherit from our parents, a gigantic

list of recipes (genes) for making proteins and protein-making machines.

Proteins do almost every chemical, structural and regulatory thing that is done in the body.

Mistakes in writing, copying or reading the recipes lead to abnormal proteins.

Types of Mutations in Human Genetic Disease Substitutions Frameshifts-deletions, insertions RNA processing mutations Regulatory mutations Expansion of trinucleotide repeat

sequences

Classification of Genetic Disorders Single-gene

disorders Chromosome

disorders Multifactorial

Disorders

Single Gene Disorders:Autosomal Dominant Marfan Syndrome Achondroplasia Huntington Disease Polycystic Kidney

Characteristics of Autosomal Dominant Inheritance Every affected person in a

pedigree has an affected parent, who also has an affected parent, and so on as far back as the disorder can be traced or until the occurrence of the original mutation.

Marfan Syndrome Marfan Syndrome

is a connective tissue disorder. One sign is arachnodactyly,long spidery fingers. Premature death is cardiac related.

Achondroplasia Note small

stature, short limbs, large head, prominent forehead, low nasal bridge, and lumbar lordosis.

Huntington Disease This is part of a

single large Venezuelan pedigree that lead to the discovery of a genetic marker for Huntington Disease.

Polycystic Kidney This photograph

shows a cross section of a polycystic kidney. Patients present with multiple symptoms related to their urinary tract.

Single Gene Disorders:Autosomal Recessive Cystic Fibrosis Phenylketonuria Sickle Cell Anemia Tay-Sachs Disease

Characteristics of Autosomal Recessive Inheritance Males and females are equally affected Disorder seen in other siblings but not

in parents or other relatives Parents are asymptomatic carriers of

mutant alleles Parents may be consanguineous

(related to a close common ancestor) especially for rare disorders

Recurrence risk is ¼ siblings

Cystic Fibrosis This cross section

of the lung of a cystic fibrosis patient exhibits mucus plugs and purulent secretions within the airways.

Phenylketonuria A classic “inborn

error of metabolism” disorder in which the lack of PAH prevents the breakdown of the amino acid, phenylalanine.

Sickle Cell Anemia A scanning electron

micrograph of red cells from a patient with sickle cell disease- the classic sickle shape is seen only when cells are in the deoxygenated state.

Tay-Sachs Disease This disorder was

named after Warren Tay, a British ophthalmologist who noted the cherry red spot in children suffering from Tay-Sachs. Bernard Sachs was a neurologist also studying this disorder.

Single Gene Disorders:X Linked Duchenne Muscular Dystrophy Hemophilia

Charcteristics of X-Linked Recessive Inheritance Incidence of trait much higher in males

than in females Heterozygous females are usually

unaffected The responsible gene is transmitted from

an affected man through all his daughters Any of the daughter’s sons has a 50%

chance of inheriting the condition A significant proportion of isolated cases

are due to new mutation

Duchenne Muscular Dystrophy

This classic “Gowers

maneuver” is used by people with muscular dystrophy to rise from the ground.

Hemophilia Subcutaneous

hematoma of the forehead of a young boy with hemophilia.

Chromosome Disorders:Aneuploidy Down Syndrome

Chromosome Disorders These disorders are not due to a single

mistake in the genetic blueprint but to an excess or deficiency of the genes contained in whole chromosomes or chromosome segments.

These are quite common, affecting 7/1000 liveborn infants and accounting for about half of all spontaneous first-trimester abortions.

Normal Male Karyotype A normal human

genome consists of 23 pairs of chromosomes, one from Mom and one from Dad.

Too many or too few chromosomes is called aneuploidy.

Down Syndrome Note the classic

facial features of a young child with Down Syndrome- the epicanthic folds, small jaw, and protruding tongue.

Multifactoral Inheritance:Genetic/Environmental Insulin-Dependent Diabetes

Mellitus

Multifactorial Inheritance There appears to be no single error in

the genetic information, but rather a combination of small variations in

genes that together can predispose or produce a serious defect, often in concert with environmental factors.

Multifactorial disorders tend to recur in families but do not show the charcteristic pedigree patterns of single-gene traits.

Genetic Disorders Affect Human Body Systems Marfan Syndrome Achondroplasia Huntington Disease Polycystic Kidney Cystic Fibrosis Phenylketonuria Sickle Cell Anemia Tay-Sachs Muscular Dystrophy Hemophilia Down Syndrome Diabetes

Cardiovascular/multiple Skeletal Nervous Excretory Respiratory Digestive Hemoglobin Formation Nervous Muscular Blood Clotting Mechanism Cardiovascular/multiple Endocrine