Gene Screening

Carriers
About one in twenty people have faulty genes which increases their chance of having a child with a serious disorder.

Inheritance
For most disorders a child is affected if both parents are carriers and both pass on their faulty gene. For others it is sufficient for the mother to be a carrier but the fault worsens when it is passed on.

Family history 
Despite the high risk to carriers, most affected children are born into families with no history of the disorder.

Tests Available

Fragile X syndrome (FXS):   The most common cause of severe learning disability after Down's syndrome.  Intellectual impairment  is severe; girls can be normal but a large proportion are impaired.  Only mothers need to be tested.  Carrier frequency 1 in 150.

Spinal muscular atrophy (SMA):   A debilitating disorder that destroys the nerve cells for walking, head and neck control, swallowing and breathing. It primarily affects children and is the main genetic cause of death in infancy. Carrier frequency 1 in 60.

Cystic fibrosis (CF):   A serious condition in which glands produce excessive amounts of thick mucus in the lungs and digestive tract. Treatment has improved but average life expectancy is still only 30-40 years. Carrier frequency 1 in 25.

Carrier status for one or more of FXS, SMA and CF can be determined in a single blood sample. 

Alef8:   Seven disorders that are relatively common in Ashkenazi Jews, plus CF, in a single blood sample. Carrier frequencies 1 in 25-100 as detailed below.

Accuracy

The rate of carriers in the population (i.e. 'frequency') and percentage of carriers with identifiable DNA faults (i.e. 'detected') are high.

*At least one of the eight Jewish disorders

Couples

Testing for SMA, CF or Alef8 can be done for couples or individuals.  For couples the man's sample is tested only if the woman is found to be a carrier.