15 Genetic Diseases

Genetic Diseases (Inherited Diseases) Zou Xiao-bing Department of Pediatrics 3rd Affiliated Hospital Sun Yat-sen University

Great changes in medicine
one of the biggest victories in medicine over the past 100 years is that infectious diseases have decreased dramatically, for example, smallpox was eradicated, poliomyelitis will soon be eradicated and pertusis , diphtheria , malaria , measles are diminishing

The reasons of the changes in medicine
Social progress
planned immunization
Advances in medical sciences
better nutrition

Genetic diseases are increasing

Reasons
Environment pollution caused by development : mutagenic substances come from industrial wastes , nuclear wastes and modern human life, drug abuse such as the use of thalidomide .
Improved diagnostic techniques include biochemical techniques, cytogenetic techniques and more important, molecular genetic techniques.

Epidemiology of genetic diseases in China
It is estimated that ,each year in China , there are 20,000,000 live birth neonates. 5% of them will suffer from inherited disorders or birth defects. it means that each year there are 1,000,000 new patients.
Over 10,000 kind of inherited diseases are found by now.

Basic of genetics
Cell is the basic unit of human body .
Chromosome is the carrier of inheritance and gene.
Normal cell contain 23 pairs chromosomes , with about 30,000 structural genes

Basic of genetics
chromosomes exist in pair, so genes exist in pair. Paired genes could be divided into dominant gene and recessive gene.
traits are controlled by the genes
One gene one enzyme theory
the abnormal chromosomes and genes result in genetic diseases.

Classification of Genetic Diseases
Chromosomal abnormalities: including euploid ,21 trisomy, 45,XO(turner syndrome) and structure abnormal such as 5P- and 14 ring.
Gene diseases including single gene diseases such as PKU and polygenic diseases such as diabetes.

Classification of Genetic Diseases
Chromosome diseases :quantity or structure of chromosome is abnormal
autosomal chromosome diseases
sex-linked chromosome diseases
Gene diseases
single gene inherited diseases (mendel model)
polygenic inherited diseases :diabetes, asthma, congenital cardiac abnormalities, cleft lip, gastric ulcer, obesity, schizophrenia etc.

Classification of single gene inherited diseases
Autosomal dominant inherited diseases
brachydactyly 、  -thalassemia, marfan syndrome
Autosomal recessive inherited diseases
PKU 、 albinism
X-linked dominant inherited diseases
G-6PD deficiency, vit-D resistant rickets
X-linked recessive inherited diseases
hemophilia 、
Y-linked trait: hairy ear syndrome

Manifestation of genetic diseases
Features in common:mental retardation 、 developmental delay, simian crease and abnormal dermatoglyphics , microcephaly and macrocephaly ,abnormal of genital organs,malformation of limb and extremities, spine and anal abnormal
specific features:fair skin and unpleasant odor of PKU, White skin of albinsim, facial abnormalities of Down syndrome and thalassemia

Diagnosis approaches of genetic diseases
Samples used
blood
amniotic fluid
skin
hair
different kind of cells
approaches
chromosome analysis
biochemical test
Enzyme analysis
gene analysis
pedigree analysis
dermatoglyphics

Treatment of Genetic Diseases
Most genetic diseases couldn’t be cured.
better care from family
better welfare of the society
function training
gene therapy has show us a bright future, ADA(Adenosine Deaminase) deficiency, can be treated by gene therapy.
(bone marrow transplantation and stem cell transplantation belong to gene therapy, ß- thalassemia can be treated by BMT)

Treatment of some single gene diseases
Restrict specific food (Dietary restriction) : PKU-phenylalanine, G6PD deficiency-broad bean and aspirine
Discharge harmful substances ( wilson disease-copper, thalassemia-iron);
Supply lacking substances (hemophilia A- factor 8)

Prevention of genetic diseases
Genetic counseling, marriage guidance and risk assessment
find the carrier of the parents with abnormal gene
prenatal diagnosis by amniocentesis and chorionic villous biopsy

DOWN SYNDROME
First described by John Langdon Down in 1866, the syndrome is named after him.
in 1956, Tijo found human cell contained 46 chromosomes.
In 1959, Lejeune identified the underlying chromosomal abnormality of affected individuals having a additional #21 chromosome.
It is the commonest chromosomal disease.
Maternal age is linked to the syndrome.

Manifestation of Down Syndrome
Facial abnormalities:small head,recessed nose, small ears and mouth
mental retardation:IQ score less than 60
development delayed ,short statue , obesity, fingers are short and stubby, simian crease on the palm
congenital heart disease and other malformations can be found in most cases.

Classification of Down Syndrome
Trisomy 21 (account for 95% of the individuals).
Translocation Down syndrome (4%)
Mosaic Down syndrome (1%)
translocation down syndrome don’t differ congnitively and medically from those with trisomy 21. but mosaic down syndrome is less severe because their trisomy cells are interspersed with normal cells.

Etiology of trisomy 21 Nondisjunction of chromosome #21 in meiosis

Etiology of translocation down syndrome During prophase of meiosis in a parent,there may be a transfer of a portion of one chromosome to another

Etiology of mosaic down syndrome death Develop to a mosaic down syndrome Nondisjunction of zygote during early stage

TURNER SYNDROME
Karyotype of turner syndrome is 45 XO
affected individuals are female in appearance , ovarian dysgenesis causing inferity, short stature, webbing of the neck, wildly spread nipples, cubitus valgus.

Klinefelter Syndrome
Karyotype is 47,XXY
the typical clinical features include male in appearance, inferity, gynaecomastia in adolessence, mental retardation, high and thin stature (usually over 180cm)

47 XYY Syndrome
Karyotype is 47 XYY
The affected individuals are male in appearance, high and thin with increased tendency to be violent and so are more common in prison or to be a hero in wartime.
END

Phenylketouria (PKU)
Autosomal recessive disease
inborn error of metabolism
reason is the lack of phenylalanine hydroxylase or an essential co-factor(BH4)
mental retardation and seizure
dietary phenylalanine restriction in early infant is very important for mental development.

Clinical manifestations of PKU
Mental retardation
seizure, irritability
abnormal EEG
fair skin
unpleasant odor of urine

Congenital hypothyroidism
Result from deficient production of thyroid hormone.
Clinical features include coarse facies,dry skin, hoarse cry, hypotonia, umblical hernia, constipation, prolonged jaundice, TSH↑ ， thyroxine↓
need life long supplement of thyroxine.

THANK YOU

45, XO TURNER SYNDROME

5p- back

Mental retardation and autism-like symptom Long face and big ears

back1 back2

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15 Genetic Diseases

by ghalan on Feb 06, 2010

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