APPROACH TO THE DYSMORPHIC CHILD

3/100 infants are born with a congenital defect, many are associated with a degree of developmental disability  genetic disorders ...

1. 3/100 infants are born with a congenital defect, many are associated with a degree of developmental disability 
2. genetic disorders and birth defects account for approximately 40% childhood deaths

History

1. prenatal/obstetrical history: maternal age and past health, alcohol/drug/meds use, difficulties during pregnancy/labour/delivery, investigations done and results (see Obstetrics Notes)
2. complete 3 generation family pedigree: consanguinity, stillbirths, neonatal deaths, specific illnesses, mental retardation, multiple miscarriages, ethnicity (thalassemia, Tay-Sachs)
3. developmental milestones and growth in an older child 

Physical examination

 

1. careful observation
2. growth parameters (height/weight/head circumference)
3. compare child's features with parents and sibs 

Investigation

1. ask for serial photographs if child is older
2. x-rays if bony abnormalities or if suspect a congenital infection
3. cytogenetic/chromosome studies +/- skin fibroblasts
4. biochemistry: specific enzyme assays
5. molecular biology for specific testing
6. genetic probes now available
   • e.g. Fragile X  counselling and recurrence risk assessment

Patterns of Inheritance

 

Autosomal dominant

1. 50% risk with an affected parent
2. e.g.
   • Marfan syndrome
   • Achondroplasia
   • Neurofibromatosis I and II

Autosomal recessive

1. risk is 25% when both parents carry the affected gene
2. carrier states can sometimes be detected; consanguinity increases chance  e.g.
   • sickle cell anemia
   • CF
   • Tay-Sachs

 

X-linked recessive

1. gene for the disease carried on X chromosome
2. inherited through mother
3. most are recessive with homozygous
4. females being rare
5. female carriers may sometimes be detected, e.g. G6PD deficiency
6. cannot have male to male transmission e.g.
   • Duchenne MD
   • Fragile X
   • G6PD
   • Hemophilia A and B

 

Multifactorial

1. genetic predisposition with environmental factors required for
   disease to be  expressed
2. recurrence risk 4-10% (disease specific)
3. if mother and one child affected, risk is up to 15%
4. e.g.
   • neural tube defects
   • cleft lip and palate

 

Mitochondrial

1. genes from mother only; M=F
2. e.g.
   • Leber optic neuropathy
   • MELAS (Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes)

 

Spontaneous mutations