Severe Combined immunodeficiency

Sickle cell disease
Sickle cell disease (SCD), which is the result of homozygous and compound heterozygote inheritance of a mutation in the -globin gene, was originally described by Herrick in 1910, although reports suggested that the ailment had been described earlier. A single base-pair point mutation (GAG to GTG) causes the hydrophobic amino acid valine to replace the hydrophilic amino acid glutamic acid in the sixth position of the -chain of haemoglobin, resulting in haemoglobin S. (HbS). SCD is the first disease to be molecularly characterised, as described by Pauling, and was confirmed to be caused by a single amino acid substitution by Ingram almost 70 years ago. Despite a well-defined Mendelian inheritance, phenotypic variation in clinical presentation is a distinctive feature of SCD. When foetal haemoglobin (HbF) lowers toward the adult level by five to six months of age, SCD is a multi-organ, multi-system condition with both acute and chronic consequences.