Genetic Disorders Fragile-X Syndrome (FXS) Prevalence Approximately 1 in 5000 births 1 in 4000 for males, 1 in 6000 for females Why? In many X linked conditions only males who inherit the abnormal gene are affected (e.g. red-green colour blindness). Fragile X syndrome is an exception, in that females can also be affected – but prevalence is lower and symptoms are less severe.

Premutation versus Full Mutation “Normal” Persons A section of the DNA in the FMR1 gene (X chromosome) repeats about 30 times.  Sequence: cytosine, guanine and guanine (CGG).  Persons with Premutation CGG repeats 55-200 times.  Persons with Full Mutation CGG repeats 200-800 times. 

38 weeks 4 pounds, 13 ounces

Small for Gestational Age More than two standard deviations below expected birth weight for gestation time for preterm and full term babies. Public Health Agency of Canada: http://www.phac-aspc.gc.ca/rhs-ssg/bwga-pnag/index-eng.php Can include: Low birth weight (LBW) < 5.5 pounds Very low birth weight (VLBW) < 3.3 pounds Extremely low birth weight (ELBW) < 1.1 pounds

Appropriate for Gestational Age (AGA) Less than 2 standard deviations below expected birth weight for gestation time. Smaller than 90th percentile of expected birth weight for gestational time. Can include: Low birth weight (LBW) < 5.5 pounds Very low birth weight (VLBW) < 3.3 pounds Extremely low birth weight (ELBW) < 1.1 pounds