background image

1

 

 

Fifth stage 

Pediatric 

Lec-7

 

أوس

 

22/2/2016

 

 

Genetics

 

 

Genetic disorders: 

common, with 2% of live-born babies having a significant congenital malformation and 
about 5% a genetic disorder  

burdensome to the affected individual, family and society, as many are associated with 
severe and permanent disability 

 

Genetically determined diseases: 

1. Single gene mutations,((Mendelian disorders) 

2. Chromosomal disorders  

3. Multifactorially inherited conditions  

4. Disorders that show an unusual pattern of inheritance  

5. Teratogenically caused conditions  

 

Mendelian inheritance: 

Disorders with these patterns of inheritance, described by Mendel in 1865, are rare 
individually, but collectively numerous, with over 15 000 single gene traits or disorders 
described 

There are three classic forms of genetic inheritance: autosomal dominant, autosomal         
recessive, and X-linked 

 

Autosomal dominant inheritance: 

This is the most common mode of Mendelian inheritance  

Autosomal dominant inheritance is determined by the presence of one abnormal gene on 
one of the autosomes (chromosomes 1–22).  


background image

2

 

 

Male and female offspring each have a 1 in 2 (50%) chance of inheriting the abnormal gene 
from an affected parent 

 

 

 

Tuberous sclerosis 

 

Marfan syndrome 

 

Neurofibromatosis 

 

Huntington's disease 

 

Retinoblastoma 

 

Waardenburg syndrome 

 

Myotonic dystrophy 

 

Familial hypercholestrolemia (LDL receptor defect Type IIa) 

 

Adult polycystic kidney disease 

 

von Hippel Lindau 

 

Familial adenomatous polyposis and Peutz Jeghers Syndrome 

 

Hereditory spherocytosis 

 

Achondroplasia 

 

Ehlor's Danlos (vascular type) 

 

Acute intermittent porphyria 

 

Hypertrophic Obstructive Cardiomyopathy (HOCM) 

 

Von Willebrand Disease 

 

Polydactyly 

 

Osteogenesis Imperfecta (Except Type VII) 

 

Hereditary hemorrhagic telengiactasia (Osler-weber-rendu syndrome) 

 

Osteopetrosis Type II (Adult type) 

 

Hypokalemic Periodic Paralysis 

 

 


background image

3

 

 

Variation in expression

Within a family, some affected individuals may manifest the disorder mildly and others 
more severely. For example, a parent with tuberous sclerosis may have mild skin 
abnormalities only, but his or her affected child may have, in addition, epilepsy and learning 
difficulties.  

 

Non-penetrance

Refers to the lack of clinical signs and symptoms in an individual who must have inherited 
the abnormal gene. An example of this is otosclerosis, in which only about 40% of gene 
carriers develop deafness 

 

 

No family history of the disorder

A new mutation in one of the gametes leading to the conception of the affected person. 
This is the most common reason for absence of a family history in dominant disorders, e.g. 
>80% of individuals with achondroplasia have normal parents. 

 

Rules of Autosomal Dominant Inheritance

Trait appears in every generation  

Each child of an affected parent has a 1 in 2 chance of being affected  

Males and females are equally affected  

Male-to-male transmission occurs 

 

Examples of Some Autosomal Dominant Disorders

Achondroplasia 

achondroplasia is the most common skeletal dysplasia in humans. The bony abnormalities 
in achondroplasia lead to short stature, macrocephaly, a flat midface with a prominent 
forehead, and rhizomelic shortening of the limbs.                       


background image

4

 

 

Neurofibromatosis Type 1

 

 

Marfan Syndrome

 

Clinical symptoms mostly involve three systems: cardiac, musculoskeletal, and 
ophthalmologic. Musculoskeletal findings include dolichostenomelia (a tall, thin body 
habitus), arachnodactyly (spider-like fingers and toes), abnormalities of the sternum 
(pectus excavatum or carinatum), kyphoscoliosis, pes planus, and joint laxity 

 

Eye findings include high myopia, which eventually can lead to vitreoretinal 
degeneration; an abnormal suspensory ligament of the lens, which can lead to ectopia 
lentis (dislocation of the lens; in Marfan syndrome, the lens usually dislocates upward 
and outward); and cataracts. Cardiac findings include a weakened aortic wall, which 
leads to progressive dilation of the aortic root. Aortic insufficiency followed ultimately 
by aortic dissection is a common complication of this disorder 

 




رفعت المحاضرة من قبل: Abdalmalik Abdullateef
المشاهدات: لقد قام 16 عضواً و 150 زائراً بقراءة هذه المحاضرة








تسجيل دخول

أو
عبر الحساب الاعتيادي
الرجاء كتابة البريد الالكتروني بشكل صحيح
الرجاء كتابة كلمة المرور
لست عضواً في موقع محاضراتي؟
اضغط هنا للتسجيل