The SIMIAN LINE: it's fundamental significance + how it became recognized as a 'minor physical anomaly'!
How come that the simian line became recognized to represent an unusual palmar line?
First of all: how to recognize a simian line? The concept of the classic simian line can be recognized to represent a 'complete' fusion between the two horizontal palmar creases (heart line & head line), leaving the presence of a single line that is featured with the impression that something appears to be missing (see picture above in left with single red line + right variant inside picture below). The prevalence of a 'complete' simian line in both hands is generally estimated to be around 1% in Europeans and up to 3% in Asians.
The simian line is known to have the highest prevalence in the so-called 'trisomy syndromes', which represent a group of genetic disorders featured with an extra chromosome that creates 'trisomy' in one of the 23 chromosome pairs. The two most common trisomy syndromes represent in respective:
- Down syndrome (trisomy 21), where the prevalence of the simian line is usually reported to be around 40%;
- Edwards syndrome (trisomy 18), where the prevalence has been confirmed to be around 70% - which is higher than in any known human (sub-)population around the world.
Interestingly, in both Down syndrome and Edwards syndrome the simian line is often featured with another (more rare) form of 'fusion' between lines - which manifests through the formation of a 'single interphalangeal crease' in the 5th digit (pinky finger): see picture below.
NOTICE: The combination of simian line + single crease on 5th finger is occasionally also present in trisomy 13, partial trisomy 9p & Cornelia de Lange syndrome.
Simian line percentages close to 50% have also been reported in e.g. the more rare trisomy 8 (Warkany syndrome) and trisomy 13 (Patau syndrome).
Beyond the extraordinary high prevalence inside the trisomy syndromes, relativel high simian line prevalence has also occasionally also been reported in a wide spectrum of diseases and disorders. This explains why the simian line became recognized as a minor physical anomaly (MPA) in medical science, which represent relatively minor (typically painless and, in themselves, harmless) congenital physical abnormalities.
Individual MPA's are known to have no specified diagnostic value; however, in combination with certain other signs (e.g. other MPAs) they can become significant for a specific disorder. For example: the combination of a simian line & single interphalangeal transverse crease (see picture above) represent a strong diagnostic sign for the presence of a trisomy syndrome. Additionally, the dermatoglyhics in the hand have been recognize to serve the purpose to finish the process of diagnosis in this perspective in order to find the one and only trisomy syndrome involved for the person - phantom pictures for the hand in trisomy syndromes are presented inside the Down syndrome section + inside the mini-course section 'diseases'.
However, the simian line in isolation from other likewisely significant signs represents in itself a relatively harmless (neutral) sign. And though rarely, it has also been spotted in the hands of a few world famous celebrities - including American actor Robert De Niro (see below), who has often been described to have a personality with strong tendency towards introversion and he described to have reliefed his shyness through performing.
NOTICE: In general, shyness as a construct is conceptually distinct from the wellknown dimensions of introversion and neuroticism - which both appear for many people not to represent quite the most favourable expressions of personality...!
the most famous simian line holder in the world; De Niro was voted in 2002 at
Filmfour.com as 'the best actor of all time', and in 2004 he was ranked as the no.1
in Empire (UK) magazine's "The Greatest Living Actor (Gods Among Us)".
Paul Broca (1877) was the first who described the unusual characteristic of the simian line (a.k.a the 'simian crease' or 'single palmar transverse crease') for the human hand. The word 'simian' refers to the fact that the hands of primates (simians) are usually featured with multiple likewise horizontal lines that transverse the full palm.
Two decades later the diagnostic significance of the simian line was established when R.L. Down discovered in 1906 that the 'single palmar crease' is a very common characteristic in Down's syndrome (after R.L. Down's father - the English physician, J. Langdon Down - had discovered Down syndrome in 1866).
During the 20th century the simian line became linked with a 'rainbow' of syndromes, diseases & other medial problems. And in modern 'Hand Analysis' the simian line has also been linked with various psychological personality characteristics (usually featured with a slight negative connotation, sometimes as a 'gift marker').
A quick summary of the effects seen in major diagnostic themes:
Simian line is 10x more common in Fragile-x syndrome
Simian line is 8x more common in Down syndrome
Simian line is 6x more common in Diabetes Mellitus
Simian line is 6x more common in Schizophrenia
Simian line is 4x more common in Neuroticism high scorers
Simian line is 2x more common in Extraversion low scorers
Simian line is 2x more common in Marfan syndrome
Simian line is 2x more common in Psoriasis
Simian line is 2x more common in Rheumatoid Arthritis
(All relative to control population prevalence statistics, which are supposed to represent the general population)
Today the (complete) simian line is known to be found in about 1 in 30 caucasian people (3%) - however, in some other populations (usually Asian populations) simian lines are more often seen - up to well above 10%. Studies in large populations have shown that the simian lines is usually almost twice more often seen in men (caucasian men: 4%) compared to women (caucasian women: 2%).
What is in 2016 the state of knowledge about simian lines? ...more.