A model for translocation inheritance in man, segregation patterns for a single centric-fusion translocation

Clinical manifestations of trisomy 4p syndrome

Trisomy 4p syndrome is a distinct clinical entity which was noted almost a quarter century ago by Wilson et al. [71] and later was delineated by Gonzalez and colleagues [29]. The variation in the length of duplicated segment usually associated with monosomy of other genetic material which has resulted in confusion and as a result a so-called 4p syndrome could not be recognized without cytogenetic analysis. We wish to draw the attention of clinicians to this subject by presenting the description of over 75 cases including one from our clinic and stress the point that molecular approaches are imperative to characterize this anomaly. After extensive review, it appears that patients retaining at least the distal two-thirds to the entire short arm share an overlapping phenotypic expression that constitutes pure trisomy 4p syndrome which includes prominent glabella, bulbous nose with flat or depressed nasal bridge, retrognathia, pointed chin, short neck with low hairline, enlarged ears with abnormal helix and antihelix, rocker-bottom feet with prominent heel. Arachnodactyly and camptodactyly. Molecular characterization of 4p is imperative. We have also included an extensive bibliography for clinicians who may find it useful as a single reference source for evaluating their future cases.

CONCLUSION

The 4p-syndrome is a distinct entity but without cytogenetic evaluation, the syndrome can not be recognized.

Comments on methods and results in: Sherman et al., "Segregation analysis of balanced pericentric inversions in pedigree data"

The analysis by Sherman et al. (1986), its basis and results have been examined. The analysis relies on general methods, which may give acceptable results under the special conditions considered by the authors, but will usually produce more or less misleading results. The program POINTER (Lalouel & Morton 1981) is shown to be based partly on a chain of irrelevant arguments for the actual context. The so-called "conventional ascertainment rules" (Morton et al. 1983) are shown to produce misleading results in cases where their assumptions are not satisfied. The mean risk for unbalanced offspring is underestimated because of an erroneous ascertainment correction. The segregation frequencies are found to be different in three national samples, contrary to the claim by Sherman et al. Only a small proportion of all information available in the data has been utilized. Alternative and more appropriate models, hypotheses and procedures have been suggested. The frequent use of packages with computer programmes of standard statistical procedures in nonstandard situations with data from collaborative studies in human cytogenetics is discussed.

Genetic risks for familial reciprocal translocations with special emphasis on those leading to 9p, 10p and 12p trisomies

An analysis of genetic risks for reciprocal translocations is given. Data from translocation families, ascertained through unbalanced offspring with trisomy 9p, 10p and 12p, were taken from the literature. The translocations were specified according to (1) the type of trisomy, (2) the degree of resulting chromosomal imbalance (partial short arm trisomies, complete short arm trisomies, complete short arm trisomies including long arm segments) and (3) the type of disjunction (2:2 or 3:1) and segregation (adjacent-1, adjacent-2; tertiary trisomy, interchange trisomy). The risks for unbalanced liveborn offspring were high for translocations leading to partial short arm trisomies through 2:2 disjunction and adjacent-1 segregation (25-29%). They were lower for translocations leading to complete short arm trisomies through the same disjunction/segregation mechanism (5-17%). Low risks were obtained for translocations, leading through 3:1 disjunction to unbalanced offspring (about 2%). For 2:2 disjunction and adjacent-2 segregation and for 3:1 disjunction the risk is significantly lower for male than for female carriers.--The frequency of balanced karyotypes compared with normal karyotypes deviated among the phenotypically normal offspring of parental carriers from the theoretical 1:1 ratio, both for translocations ascertained through trisomy 12p and trisomy 10p.--It was demonstrated that the genetic risk for reciprocal translocations depends exclusively on (1) the degree of possibly resulting genetic imbalance and (2) the probability of the disjunction/segregation mechanism leading to this type of imbalance. Both factors can be predicted from the position of breakpoints.--The precision of breakpoint localizations and its impact on the risk estimation are also considered.--Finally, general rules for genetic counselling of families with reciprocal translocations are indicated.

4p trisomy syndrome: report of 4 additional cases and segregation analysis of 21 families with different translocations

Thirty reports of partial 4p trisomy have been published. The manifestations and cytogenetic findings in four additional cases from two families are described in the present paper. Segregation analysis has been performed on the 21 families reported to date. The risk of having unbalanced offspring was the same in carrier mothers and carrier fathers. The risk of trisomic offspring was 14%. Among phenotypically normal progeny, normal karyotypes and balanced translocation states occurred with about equal frequency.

Reproductive risk of t(13q14q) carriers: case report and review

We report a four-generation kindred with a balanced 13q14q Robertsonian translocation. The proband had the Down sydrome, due to trisomy of chromosome 21; he also carried the balanced D-group translocation. S segregation analysis of 86 sibships was performed to examine the risk of t(13q14q) carrier parents having trisomy 21, 47,XXY, or trisomy 13 children by which a number of families were ascertained. None of these disorders recurred after birth of the propositi. The frequency of abortions was not different from that of the general population. The conditional segregation ratio for balanced translocation carriers among the phenotypically normal offspring of carrier parents was 0.55 +/- 0.04.

Risk for short arm 10 trisomy. A segregation analysis of eleven families with different translocations

A segregation analysis has been carried out for 11 families with trisomy 10p caused by familial translocations involving a segment of the short arm of chromosome 10. The theoretical basis for the analysis is considered in some detail. No differences were found between the segregation pattern in the offspring of carrier mothers and that of carrier fathers. There was a high risk for offspring with trisomy 10p (22%). A phenotypically normal descendant also has a high risk of becoming a balanced translocation carrier (71%). This result does not deviate significantly from the theoretical value of 50%.