FISH

SMALL SUPERNUMERARY MARKER CHROMOSOMES

-  sSMC -

BASICS - FREQUENCY

 

Frequency of sSMC

-   in newborn
-   in prenatal cases
-   in mentally retarded
-   in subfertile people
-   if sSMC is de novo
-   if sSMC is acrocentric derived
-   of one single UK facility
-   if ring chromosome shaped
-   according to their chromosomal origin

 


Frequency of sSMC in newborn

Overall, in newborn cases the rate is 0.044% [157]


some examples from literature:
0.026% (16 in 59952 newborn infants) {1 here are taken together: 17-18, 22-27}
0.024% ( 4 in 16395 newborn infants) {2}
0.123% ( 8 in 6500 newborn infants) {3}
0.040% ( 3 in 7536 newborn infants) {4-6 taken together according to 3}
0.054% ( 6 in 11148 newborn infants) {7}
0.069% (24 in 34910 newborn infants) {19; 62}
0.027% ( 4 in 14835 newborn infants) {98}
0.219% ( 4 in 1830 newborn infants) {125}
0.000% ( 0 in 930 newborn infants) {126}
0.027% ( 1 in 3665 newborn infants) {143}

According to {142} sSMC occur
- in 27.7% of aborted fetuses (9/46 cases)
  but only
- in 9.2% (7/76 cases) of term births

 

References 

 


Frequency of sSMC in prenatal cases

Overall, in prenatal cases the rate is 0.075% [157]

 

- In Ref. {153} 20 sSMC were found in 15792 prenatal cases
  The cases were studied due to
  + advanced maternal age [54.16%],
  + increased risk acc. to triple test [19.27%],
  + pathologic ultrasound finding [14.26%], or others

- According to {16} the higher rate of cases with sSMC in prenatal compared to newborn can be due to
  (1) the bias caused by the maternal age effect in prenatal series,
  (2) the fact that prenatal diagnosis is sometimes performed due to known or suspected fetal pathology, and/or
  (3) severely affected fetuses may result in miscarriages and will therefore not be included among newborns.

- According to {142} - a study done in 1997 - ~50% of pregnancies with sSMC were terminated; 4.4% of the remaining pregnancies ended with stillbirth or spontaneous abortion; the rest of the children wer born clinically normal.

- According to {116} - a study done  in 2004 - 20% of pregnancies with cytogenetic aberrations (419 cases) are terminated; 31% of the cases with de novo sSMC are selectively terminated!

- According to {166} - a study done  in 2003:
  in 7/7 inherited sSMC pregnancy continued
  in 8/17 pregnancies with de novo sSMC pregnancy was terminated - i.e. ~50% were terminated in this Italian study

- According to {158} an sSMC was present in 1/13 pregnancies with exomphalos.

- According to {159} an sSMC was present in 1/70 pregnancies with cleft palate.

 

References

 


Frequency of sSMC in mentally retarded

 

Overall, in mentally retarded patients the rate is 0.288% [157]

 

- one single center study found a rate of 0.118%
  (in 32930 patients karyotyped in the Belgium center for Human Genetics between 1966 and 1981) {48}

 

References

 


Frequency of sSMC subfertile people

 

Overall, in sub fertile people the rate for male and female together is 0.125% [157]
but it differs with 0.165% in male versus 0.022% in female.

 

- in Ref. 69 it is suggested that sSMC could disrupt human spermatogenesis - in  {142} the influence of sSMC on non-disjunction is discussed.

- 644 cases with autosomal sSMC collected in that page by 13.Nov. 2004 were specified by their gender: 322/644 where male an 322/644 female

 

References

 


Frequency of sSMC if sSMC is de novo

Overall, 70% of sSMC are de novo [157]

 

- 77% of sSMC are de novo (172 in 241 cases)  - 16% maternally, 7% paternally inherited {151}.

- According to {53; 94} no discernibly increase risk for fetal abnormalities if sSMC is also present in a phenotypically normal parent.

- According to this page (12/06/2005) 918/1872 de novo; 111/1872 inherited 943/1872 no information available; i.e. de novo -> 89.2%; inherited ->10,8%. This hreflects the ascertainment bias present in the sSMC cases collectable on this page. But: 66/111 sSMC cases are of maternal origin; 39/111 are of paternal origin; 6 familial -> concordance with {151}

- 0.125% (3 in 2,400 adult healthy persons; 2 of the 3 cases were familial) had a de novo sSMC {29}

 

References

 


Frequency of sSMC if sSMC is acrocentric derived

Overall, 70% of sSMC are acrocentric derived [157]

 

86%       (i.e. in 38 of 44 cases) {2}
81%       (i.e. in 17 of 20 cases) {16}
45%        with satellites (i.e. 14 of 31 cases) {16}
68%       (i.e. in 26 of 38 cases) {46}

among mentally retarded
50% with satellites (i.e. 27 of 54 cases){91}

 

References

 


Frequency of sSMC of one single UK facility (Dr. Crollas group {147})

 

137 patients with sSMC
- 37% with abnormal phenotype
- 7% couples with reproductive difficulties
- 47% antenatal diagnosis
- 9% miscellaneous

- 59% mosaics - 41% no mosaics

- 70% de novo; 19% maternal origin; 11% paternal origin (of 109 of the cases)

- 36% derived from non-acrocentrics (of 112 cases studied by FISH)

- 35% derived from #15; 9% from #22

 

sSMC(15) appearance seems to be associated with advanced maternal age

 

References

 


Frequency of sSMC if ring chromosome shaped

 

- 10% (i.e. 3 of 31 cases) {16}

- 60% of case with sSRC are associated with an abnormal phenotype {77}.

- Apart from the shape a ring is characterized by: "the detection of anaphase bridges and micronuclei in the monolayer fibroblast culture" {64}

- sSRC per definition do not have telomeric sequences {78; 79}

- Ring chromosomes can also have telomeric sequences {169}.

 

References