Young: Medical Genetics 
Multiple Choice QuestionsYoung: Medical Genetics
Chapter 7
John Dalton
Reverend Dr WIlliam Spooner
John Dalton (1766-1844)
Photo of John Dalton
John Dalton was born in Cumberland close to the region of England known as the Lake District, and lived most of his life in Manchester, where he taught and undertook research in the many aspects of science that captured his interest and imagination. Most notable amongst these was chemistry, specifically the fundamental structure of elements, and in the scientific community he is best remembered for his proposal of basic atomic theory, i.e. that elements are composed of atoms and that atoms of different elements combine to form compounds.
While this was undoubtedly his outstanding achievement, Dalton is also honoured in biological circles for his thoughts on colour blindness, the subject of the first of his many scientific presentations. Dalton was himself colour blind, as was his brother, so that he was able to provide a meticulous description of how he differed in his interpretation of various shades of the spectrum, resulting on occasions in the purchase of clothing of a totally inappropriate and embarrassing colour. He noted that males were affected more often than females and attempted to account for his unusual perception of colours by proposing that his vitreous humour was tinted blue. This would result in the selective absorption of longer wavelengths (green and red). His enthusiasm for this theory was such that he requested that his eyes be examined after his death to determine whether his vitreous humour was indeed tinted. Given that the basic defect is now known to lie in the retina, it is not surprising that Dalton’s vitreous humour was found to be crystal clear.
In 1995, almost exactly 200 years after his presentation on “extraordinary facts relating to the vision of colour”, DNA was extracted from one of Dalton’s eyes and found to be lacking in a normal copy of the green pigment gene, thereby providing molecular confirmation of deuteranopia. As outlined on page 147, this is the most common form of red-green colour blindness. It is usually caused by recombination between the misaligned red and green colour pigment genes in meiosis.
Although Dalton’s original theory on the cause of colour blindness was incorrect, because of his detailed description of the condition, his name has been strongly associated with it to the extent that for many years colour blindness was widely referred to as ‘Daltonism’. It is a little strange that the man who propounded the fundamentals of basic atomic theory should be remembered equally well for his description of what is little more than a biological curiosity.
Reference
Hunt DM, Dulai KS, Bowmaker JK, Mollon JD (1995) The chemistry of John Dalton’s colour blindness. Science, 267, 984-988.
Reverend Dr William Spooner (1844-1930)
On page 138 reference is made to William Spooner who has achieved immortality and an eponymous entry in the Oxford English dictionary as a consequence of his jumbled, and on occasions, amusing, misuse of his native tongue. Born in London, he attended New College Oxford, first as a student and later as lecturer, dean and warden. He also qualified as an Anglican priest.
Amongst his students Spooner gained a reputation as a kind and perhaps somewhat eccentric individual whose brain and speech were not always in perfect synchrony. This manifested in the form of a number of potentially embarrassing faux pas such as his toast to Queen Victoria ‘Three cheers for our queer old dean’ and reference to ‘Our lord’ as ‘a shoving leopard’ These examples of reciprocal transposition of the first letters of closely adjacent words soon came to be known as ‘Spoonerisms’.
These curious linguistic quirks may simply have been a consequence of a racing brain which could cerebrate much more rapidly than its owner’s tongue could articulate. However there is an alternative explanation. Spooner had oculocutaneous albinism (OCA). This is now known to comprise a genetically heterogeneous group of disorders, in all of which vision is poor due to nystagmus and an associated defect in optic tract decussation. This poor visual acuity with misrouting of the visual pathways at the optic chiasm might well have compromised Spooner’s ability to synthesise and articulate written notes with consistent precision.
OCA is generally a relatively mild disorder although those affected have to be careful to avoid direct sunlight and its attendant risk of skin cancer. The two common forms, OCA1 and OCA2, both show autosomal recessive inheritance. OCA1 is due to reduced or absent activity of tyrosinase, an enzyme essential for melanin synthesis (p 208). OCA2 is caused by defects in a gene that encodes a melanosome membrane transporter known as Protein P. The OCA2 locus lies within the Angelman/Prader-Willi syndrome microdeletion region on chromosome 15q11-13 (p. 64, 85-86). Approximately 1% of individuals with these conditions also have OCA as a result of unmasking of the carrier state by loss of the normal ‘wild-type’ allele in the deletion.
Reference is also made on page 138 to the possibility that Noah may also have had OCA. At birth he was described as being ‘whiter than snow’ and ‘redder than the rose’, with hair ‘whiter than white wool’ and eyes ‘like the rays of the sun’. The case for a diagnosis of OCA in Noah has been cogently argued by Arnold Sorsby, a Professor of Ophthalmology based in London, on the basis of his review of ancient religious writings.
Reference
Sorsby A (1958) Noah – an albino. British Medical Journal, 1587-1589.
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