الفهرس 
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Abstract
Mental retardation (MR) is defined as subaverage intellectual functioning which originates during the deve¬lopmental period and which is associated with impairment in adaptive behaviour (Turner et al.1983)-^^
Statistical analysis in institutions for MR showed an excess of MR males than females, also mentally retarded boys were more likely to have affected brothers than were girls to have sisters- This was suggested to be due to X-LMR (Dewey et al,1965, Gerald,ig80).^
It is now possible to divide families having X-LMR into two groups, those having a fragile(X) chromosome i.e. fragile (X) syndrome which is the most common hereditary form, as it affects 1/3 to 1/2 of all families with X-LMR (Rhoads et a.1,1982)^^ and those not having such a marker i.e. fra(X) -ve X-LMR which are more than fifty disorders but with rare frequencies (Sutherland,1977).
Fragile sites on chromosomes are points at which the chromosome is liable to break:. They may be heritable fra. sites (rare, segregate in mendelian fashion e„g Fra X 27) or common fra sites (frequent, caused by environmental factors as radiation)(Le Beau,1986)^61^
The fragile X chromosome results from fragile site at ^”q27f ”^at is toward the end of the long arm of the X chromosome (Harvey et al.1977)-^12^ The only key to diagnose fragile (X) syndrome is the detection of the fra(X) chromo¬some in at least 4f° of cultured lymphocytes (Jacobs et al. 1980).(66)
This study w^s carried out in order to estimate the contribution of the fra(X) syndrome to non specific IV1K and to evaluate the presence of the marker (X) in female carriers. 23 patients (in 15 families) presenting with non specific MR are included in this study. These cases were subjected to clinical examination, anthropometric measure¬ments, dermatoglyphics, biochemical screening, EEG, esti-mstion of the IQ, clinical photography and cytogenetic examination.
Cytogenetic examination was done for all affected males, carrier females & a control group. It included routine blood culture (to detect chromosomal abnormalities) and two special techniques, FudR technique and Medium 199 technique, to detect the folate sensitive fra sites (mainly
fra X or?).
q27
from the studied 23 cases, 12 cases were found to be (+ve) for the fra(X) chromosome, and 11 cases were found to be(-ve) .71.4^ of fra(X) +ve cases and 25L/o of fra(X) -ve MR males had positive family history of similar cases.
As regards the phenotype of fra(X) males, MR was found to be the most common feature. Adult fra(X) males typically have long face, large or prominent ears, promi¬nent mandible and macroorchidism. In this study, 75^ of
the fra(X) +ve postpubertal males showed mareoorchidism, in contrast no macroorchidism was found in fra(X) -ve MR males.
Urine screening and thin layer chromatography revealed normal results in all the studied cases.
Cytogenetic studies showed that FudR technique was more efficient in detecting the fra(X) chromosome than medium 199. Age is a factor in demonstrating the fra(X) chromosome in carrier females but not in affected males. A higher proportion of fra. (X) chromosome was seen in mentally retarded males (3$ -38$) than in females (ly»~8$)j the proportion of cells expressing the fra(X)chromosome had no significant effect on the IQ level of fra(X)+ve males.
As regards dermatoglyphic findings in fra(X) males,a significant difference was found in finger prints, a-b and t-d ridge counts, patterns on toes and soles. Non significant difference was found in total ridge count, palmar pattern intensity index, atd angle and palmar patterns.
It was concluded that detailed cytogenetic examination by special techniques in all cases suffering from non specific MR must be done to diagnose frs(X) +ve ms.les and female carriers, and hence proper genetic counselling can be applied.