Otto L Mohr.

A new type of hereditary brachyphalangy in man online

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in earlier publications concerning heredity in man. A limited examina-
tion might indeed have given a conception of a very marked "weaken-
ing" of brachyphalangy when the data collected from now living mem-
bers of this line were compared with the description of the character
found in the family book and with the photograph from generation II
(fig. 3). The introduction of modifying factors in later generations
(e. g., as that found in this case) would give exactly this impression.



HEREDITARY TYPE OF CHARACTER STUDIED. 61

It is hardly necessary to emphasize further the hypothetical character
of the interpretation here given. In human material where experiments
are excluded the only way is to test whether the carefully collected
data are in accordance with the principles sufficiently well established
through experimental genetic work. This is what has been done here
and the result is positive.



VII. SUMMARY.

The investigation deals with a symmetrical shortening of the second
phalanx of the second fingers and toes inherited within a Norwegian
family, some members of which emigrated to North America.

The malformation is always restricted to this phalanx only, a rela-
tion which makes the character especially favorable for genetic investi-
gation, since an exact numerical expression for the character studied
can be obtained by direct measurements from the radiographs.

The hands and feet are in every other respect perfectly normal. The
affected individuals show no shortness of stature.

The anomaly manifests itself under two distinctly different somatic
types, one " slightly" shortened, so-called B-type, which is generally
overlooked by the affected individuals, and one very "much" shortened,
so-called B !-type, which is very striking in its somatic appearance.
No case of an intermediate condition has been observed.

In the affected phalanges of the B-type there is no premature ossi-
fying of the epiphysial cartilages. Radiographs from hands of children
having the B !-type brachyphalangy demonstrate at the age of 12 years
a total ossification of the epiphysial cartilage of the affected phalanx.

The inheritance of the malformation is followed without any break
through 6 generations, including and descending from an individual
born in 1764. The lines descending from one affected daughter and
one affected son of this individual form the main subject for the present
investigation. Within these lines every individual is recorded. In
addition, several families belonging to the IV, V, and VI generation,
descending from another affected son, are discussed.

A detailed family record is presented with exact information also
concerning the earlier generations. This was possible, because the
family owns an old "Family book" with elaborate information con-
cerning each individual belonging to the earlier generations.

The photographs of brachyphalangy cover 5 generations, the radio-
graphs cover 4.

The brachyphalangy is inherited as a dominant, not a sex-linked
character. The numerical ratio between the affected and unaffected
individuals in the offspring of brachyphalangous members of the
family is in accordance with the theoretical expectation.



62 SUMMARY.

All the brachyphalangous individuals are heterozygous for the gene
in question, with one possible exception. This individual resulted
from an intermarriage within affected lines, and therefore may have
been homozygous for the factor for brachyphalangy. She was a cripple
without fingers and toes and was unable to develop. She died at the
age of one year.

Analogous cases from experimental genetic work, demonstrating a
distinct difference in the appearance of the somatic character when
the genes are homozygous from that of the heterozygous condition,
and the lethal effect of many dominant genes when homozygous are
discussed in this connection. Emphasis is laid on the importance of
this experience from a medical point of view.

The material includes one case of identical twins, both brachypha-
langous of an identical type.

Based on the numerous measurements from the radiographs, an
analysis of the two types of the malformation was possible. Much
attention has been paid to this special point. It was found that the
B-type of brachyphalangy may overlap the limit of extreme variation
in normal hands i. e., some individuals heterozygous for the gene for
brachyphalangy (which generally causes a very characteristic altera-
tion of the hand) may be somatically normal. The conclusive demon-
stration of this fact was obtained in one case where the radiographs
gave normal measures while the genetic test, which was at the same
time at hand, proved the individual to be heterozygous for the gene
for brachyphalangy.

A genetic explanation of the occurrence of the B-type and B !-type
is suggested. Based on analogies from experimental genetic work, the
two types are explained through the presence in some of the normal
individuals, married into the family, of a dominant specific modifying
gene which enhances the effect of the principal gene for brachyphalangy
and changes the B-type into a B !-type.

Indications in favor of this view are presented from the earlier
literature concerning hereditary brachyphalangy in man which deals
with types of brachyphalangy different from the one here studied.
The review of this literature includes both "pre-Mendelian" and
"post-Mendelian" publications demonstrating inheritance of these
malformations in accord with Mendel's laws.



LIST OF LITERATURE.

BAUR, E. 1914. Einfiihrung in die experimentelle Vererbungslehre. 2 Aufl., Berlin, 1914;

pp. 1-401.
BRIDGES, C. B. 1916. Non-disjunction as a proof of the chromosome theory of heredity.

Genetics, vol. 1, pp. 1-52, 107-163.
CASTLE, W. E. 1905. Characters in guinea-pigs and rabbits. Carnegie Inst. Wash.

Pub. No. 23, pp. 1-78.
and C. C. LITTLE. 1910. On a modified Mendelian ratio among yellow mice.

Science, n. s., vol. xxxii, pp. 868-870.
, and S. WRIGHT. 1916. Studies of inheritance in guinea-pigs and rats. Carnegie

Inst. Wash. Pub. No. 241, pp. 1-196.
CLARKE, D. S. 1915. Congenital hereditary absence of some of the digital phalanges.

Brit. Med. Jour., vol. n for 1915, p. 255.
CRAGG, E., and H. DRINKWATER. 1916. Hereditary absence of phalanges through five

generations. Jour, of Gen., vol. 6, pp. 81-89.
COLSON, . 1882. Microdactylie. Ann. de la Soc. de Med. de Gand., p. 202. Ref. by

Leboucq, 1896.
CUENOT, L. 1905. Les races pures et leurs combinaisons chez les souris (4me note).

Arch, de Zool. exp. et ge"n., 4e s6r., t. m, notes et revue, pp. cxxiii-cxxxii.
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Zool. exp. et ge"n., 4e s4r., t. vi, notes et revue, pp. i-xiii.
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note). Arch, de Zool. exp. et ge*n., 4 se"r., t. ix, notes et revue, pp. vii-xv.
DAVENPORT, G. C., and C. B. DAVENPORT. 1910. Heredity of skin pigment in man.

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DAVENPORT, C. B. 1913. Heredity of skin color in negro-white crosses. Carnegie Inst.

Wash. Pub. No. 188, pp. 1-106.
DETLEFSEN, J. A. 1914. Genetic studies on a cavy species cross. Carnegie Inst. Wash.

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Edinburgh, vol. xxvin, part 1, pp. 35-57.
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vol. n, pp. 21-40.

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Amer. Nat., vol. XLIV, pp. 173-181.
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pp. 160-174.
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Peabody Mus. Harvard Univ., vol. in, pp. 65-78.
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Archivio di Orthopedia, 1902, p. 119. Ref. in Arch. f. Orthop. 1903. Bd. 1.
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a. d. Geb. d. Rontgenstr., Bd. 7, pp. 273-276.
HOLMGREN, T. 1910. Uber den Einfluss der Basedow'schen Krankheit und verwandter

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vni, Uber die Ossification der Hand und die friihzeitigere Verknocherung der

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63



64 LIST OF LITERATURE.

JOACHIMSTHAL, G. 1900. Die angeborenen Verbildungen der oberen Extremitaten.

Fortschr. a. d. Geb. d. Rontgenstr., Erganzheft. 2, pp. 1-40.
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Rontgenbildern. Fortschr. a. d. Geb. d. Rontgenstr., Bd. 9, pp. 351-355.
KUMMEL, W. 1895. Die Missbildungen der Extremitaten durch Defect, Verwachsung

und Uberzahl. Bibliotheca Medica, Abt. E, Heft 3, pp. 1-84.
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LXJNDBORG, H. 1913. MedizinischbiologischeFamilienforschungeninnerhalb eines2232

kopfigen Bauerngeschlechtes in Schweden. Jena 1913. Pp. 1-740.
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vol. 19, pp. 61-98.

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MACHOL, A. 1907. Beitrage zur Kenntniss der Brachydactylie. Mitteil. a. d. Grenzgeb.

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old. Amer. Jour. Anat., vol. v, pp. 433-458.
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Zeitschr. f. Morph. u. Anthrop. Bd. 2, pp. 77-157 and pp. 365-678.
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d. Geb. d. Rontgenstr., Bd. 7, pp. 94-98.
WALKER, G. 1901. Remarkable cases of hereditary anchyloses or absence of various

phalangeal joints with defect of the little and ring finger. Johns Hopkins Hosp

Bull., 12, pp. 129-133.
WRIEDT, CHR. 1914. Die kurzohrige Schafrasse Norwegens. Jahrb. f. wissenschaft. u.

prakt. Tierzucht., 9 Jahrg.
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f. d. Norske Landbr., 23 AArg., p. 622.
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u. Vererb. lehre. Bd. xx, pp. 262-263.



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Online LibraryOtto L MohrA new type of hereditary brachyphalangy in man → online text (page 7 of 7)