Brachydactyly type D, also known as short thumb or stub thumb and inaccurately referred to as clubbed thumb, is a condition clinically recognised by a

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

being relatively short and round with an accompanying wider nail bed. The

distal phalanx The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

of affected thumbs is approximately two-thirds the length of full-length thumbs. It is the most common type of

brachydactyly Brachydactyly (Greek βραχύς = "short" plus δάκτυλος = "finger"), is a medical term which literally means "short finger". The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an in ...

, or shortness of digits, affecting approximately 2–3% of the population, and is associated with the ''

HOXD13 Homeobox protein Hox-D13 is a protein that in humans is encoded by the ''HOXD13'' gene. This gene belongs to the homeobox family of genes. The homeobox genes encode a highly conserved family of transcription factors that play an important role in ...

'' gene, located on chromosome 2q31.1

Physiology

Brachydactyly Brachydactyly (Greek βραχύς = "short" plus δάκτυλος = "finger"), is a medical term which literally means "short finger". The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an in ...

type D is a skeletal condition which exhibits a 'partial fusion or premature closing of the epiphysis with the

of the thumb', according to Goodman '' et alia'' (1965). J.K. Breithenbecher (1923) found that distal phalanges of stub thumbs were one-half the length of full-length thumbs, while R.M. Stecher (1957) claimed that it is approximately two-thirds. The condition may either be unilateral (affecting one thumb) or bilateral (affecting both).

Genetics

A genetic trait,

type D exhibits

autosomal dominance In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

and is commonly developed or inherited independently of other hereditary traits. The condition is associated with the ''

'' gene, which is central in

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...

formation and growth. Various other studies supported an autosomal dominant pattern with reduced penetrance.

Hereditary trait

A 1965 scientific study in

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

found that 3.05% of Israeli Arabs had one or two stub thumbs, compared with 1.57% among

Ashkenazi Ashkenazi Jews ( ; he, יְהוּדֵי אַשְׁכְּנַז, translit=Yehudei Ashkenaz, ; yi, אַשכּנזישע ייִדן, Ashkenazishe Yidn), also known as Ashkenazic Jews or ''Ashkenazim'',, Ashkenazi Hebrew pronunciation: , singu ...

as well as non-Ashkenazi

Jews Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...

. However, as the survey's Arab test persons were mainly recruited from a handful of large and closely related clans living in a particular village, said percentage should be "considered with some reservation," according to Goodman ''et al.'' (1965). Cases of stub thumbs have also been found in Eastern Nepal for Jirel ethnic individuals from their participation in various epidemiologic studies. Some studies included taking radiographs of hands and wrists to examine their skeletal structure. Of the studied sample (which included 2,130 participants; 969 male and 1,161 female), 3.55% were found to have brachydactyly type D.

Terminology

The condition is known under numerous names. The most commonly used name is clubbed thumb, or club thumb. American researcher R.A. Hefner used the terms "short thumb" and "brachymegalodactylism" in 1924, and "short thumb" has continued to be used in a few other studies since then, including the study that defined

Rubinstein–Taybi syndrome Rubinstein–Taybi syndrome (RTS) is a rare genetic condition characterized by short stature, moderate to severe learning difficulties, distinctive facial features, and broad thumbs and first toes. Other features of the disorder vary among affect ...

in 1963. "Stub thumb" is the common term preferred by the online database Online Mendelian Inheritance in Man and was first used in a 1965 study. Stub thumbs have also been called murderer's thumb (allegedly among

fortune tellers Fortune telling is the practice of predicting information about a person's life. Melton, J. Gordon. (2008). ''The Encyclopedia of Religious Phenomena''. Visible Ink Press. pp. 115-116. The scope of fortune telling is in principle identical wi ...

), bohemian thumb, toe thumb, and potter's thumb. The term "clubbed thumb" should not be confused with

nail clubbing Nail clubbing, also known as digital clubbing or clubbing, is a deformity of the finger or toe nails associated with a number of diseases, mostly of the heart and lungs.Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. ...

, which is a clinical sign associated with a number of diseases.

References

{{Congenital malformations and deformations of musculoskeletal system Fingers Irregular bones