Children homozygous recessive for this allele rarely survive past five years of age. This lipid accumulates in lysosomes in brain cells, eventually killing the brain cells. Sickle-cell anemia is an autosomal recessive we have discussed in other sections. The recessive allele causes a single amino acid substitution in the beta chains of hemoglobin . When oxygen concentration is low, sickling of cells occurs.
Achondroplastic dwarfism occurs, even though sufferers have reduced fertility.
The disease usually does not manifest until after age 30, although some instances of early onset phenomenon are reported among individuals in their twenties. Polydactly is the presence of a sixth digit. In modern times the extra finger has been cut off at birth and individuals do not know they carry this trait. One of the wives of Henry VIII had an extra finger. In certain southern families the trait is also more common.