On the basis of linkage studies, the gene of human triose-phosphate
isomerase (TPI) EC 18.104.22.168. has been assigned to chromosome 12 (Jongsma et al.,
1974). By hybridization experiments it has been further localized on the 12pter
? 12q14 region (Jongsma et al.,1975). We can now define its position
:12pter ? 12p12.2. This conclusion results from quantitative estimation
of TPI activity in 3 patients with different aberrations of chromosome 12.
Materials and Methods
The enzymatic activity of triose-phosphate isomerase has been assayed
in three patients carrying a rearrangement of the short arm of chromosome
Case No. 1 is a male of 2 years 4 months with trisomy of the segment
12pter ? 12q12 due to malsegregation of a maternal translocation
t(12;14) (q12;p11). This patient's observation has been already reported
(Réthoré et al., 1975),
Cage No. 2 is a newborn male with trisomy of the segment 12pter
? 12p12.1 due to malsegregation of a maternal translocation t(12;15)
(p12; p11;1) (unpublished observation).
Case No. 3 is a 4-year-old male, with monosomy of the segment 12p11
? 12p12.2, whose observation has been already reported (Malpuech et al.,
Table 1 shows results concerning genes already assigned to chromosome
12 : triosephosphate isomerase (TPI), lactate dehydrogenase B (LDH P) (Malpuech
et al., 1975; Réthoré et al.,1975) and glyceraldehyde 3 phosphate
dehydrogenase (G3PD) (Réthoré et al., 1976). We also include, as controls,
glucose 6 phosphate dehydrogenase and 6 phosphogluconate dehydrogenase,
respectively assigned to chromosome X and chromosome 1 (Jangsma et al., 1973;
First Internat. Workshop on Human Gene Mapping, 1973).
Table 1. Red cell enzyme activity estimated according to
||Case No. 1Trisomy 12pter ?
12q12||Case No.2Trisomy 12pter ? 12p12.1||Case No.
3Monosomy 12p11 ? 12p12.2
|Triose phosphate isomerase
|InTris pH 8 (N= 1673 ±
|In sodium phosphate pH 7.5 (N = 2765 ±
|Glyceraldehyde 3 phosphate dehydrogenase N=206 ±
29||314 ||352 ||224 173
|Lactadehydrogenase N = 100 ±
|Glucose 6-phosphate dehydrogenase N = 11.9 ±
|6 Phosphogluconate dehydrogenase N = 9.1 ±
|Results are expressed in lU/g Hb
Red cell TPI and G3PD activities are significantly increased in cases
1 and 2, while they are within normal limits in case 3. In contrast LDH, which
is increased in cases 1 and 2, is significantly decreased in case 3. In
addition, a study of TPI repeatedly showed an increased activity of leukocytes
and fibroblasts in patient 1 (data not shown).
The excess of genetic material for chromosome 12 involves the short
arm in its full length in case 1 and only the distal part in case 2. In case 3,
there is a loss of genetic material, involving the proximal part. Only a short
segment in the middle part of the short arm is concerned in all three
aberrations, and, according to our previous results, the gene coding for LDH B
was thereby assigned to this segment (Réthoré et al., 1975). Further
investigations allowed us to localize G3PD on the distal segment (Réthoré et
al., 1967). Since the results for TPI are similar to those obtained for G3PD,
it is likely that the gene coding for TPI is located on the same distal segment
of the short arm of chromosome 12 (Fig. 1).
As far as in chromosome aberrations gene dosage effect can provide a
reliable clue to precise gene localisation (Junien et al.,1976), we suggest
that the TPI locus, like G3PD, is between 12pter and 12p12.2.
Fig. 1. Localization of TPI, G3PD, and LDH-B on the chromosome 12 short
arm. R banding according to Dutrillaux and Lejeune (1971)