What causes Congenital Hand Differences? (CHDs)
This blog is here to provide simple, helpful information on how and why hand differences occur to parents and carers of children born with hand differences.
What are CHDs? Congenital Hand Differences are hand differences that occur from birth where a child is born with a hand that is formed differently to what is commonly expected. The term "difference" is used rather than "abnormality" as this is what the childs hand is, different to others rather than abnormal. A CHD occurs in approximately 1 in 2000 live births.
How do CHDs happen? Embryology is a branch of medicine and biology that studies of how a foetus develops. Hands are formed between weeks 4 and 8 of a woman's pregnancy with webbing initially present between the digits which typically recedes by week 10. A network of signals are used by the foetus to work together to form the hand; this happens in three directions to create a fully developed human hand. One of the most important regulators of this development is a protein called sonic hedgehog (SHH) which really is named after the video game character. The amount of SHH the hand, and then the digits, receive determines the size and shape of them (1). If there is too much or too little SHH the hand can develop differently, resulting in a CHD.
Why does this happen?
Depending on where and when in the growth pathway signals differ, development of the upper limbs and hands will be affected in different ways. It is not currently clear exactly why CHD's happen, but this may be due to genes "planning" foetal development in the womb or it could be environmental depending on the womb itself or the external environment. However, most CHD's happen for unknown reasons that are not related to genes of the behaviour of parents so remember, in the majority of cases, parents are not to blame for CHDs happening.
(1) Anderson, Eve, et al. “Human limb abnormalities caused by disruption of hedgehog signaling.” Trends in Genetics, vol. 28, no. 8, 2012, pp. 364–373., doi:10.1016/j.tig.2012.03.012. Web. 6 Mar. 2018.
Sheeba, Caroline J., et al. “Getting a handle on embryo limb development: Molecular interactions driving limb outgrowth and patterning.” Seminars in Cell & Developmental Biology, vol. 49, 2016, pp. 92–101., doi:10.1016/j.semcdb.2015.01.007. Web. 6 Mar. 2018.
Lettice, Laura A., et al. “The Conserved Sonic Hedgehog Limb Enhancer Consists of Discrete Functional Elements that Regulate Precise Spatial Expression.” Cell Reports, vol. 20, no. 6, 2017, pp. 1396–1408., doi:10.1016/j.celrep.2017.07.037. Web. 6 Mar. 2018.