| المستخلص: |
Down syndrome (DS) is the most common and best-known chromosomal disorder and is the single most common genetic cause of mental retardation. Governmental care of this syndrome and other handicapping conditions has increased tremendously in the past few years to the extent that DS phenotype has became a phobia and many parents and/or physicians referred normal babies for karyotype for suspicion of chromosomal anomalies or for reassurance of their parents. On the other hand, prenatal screening is still inaccessible to most families and almost all cases of Down syndrome are diagnosed postnatally. In this paper we present the first and the largest study on DS patients referred to Medical Genetics Center from different regions and discrete all over Egypt aiming to look for possible causal factors for this high birth rate, and to evaluate the trend of parents and clinicians to the new screening programs and prenatal diagnosis. The study was included 1100 patients referred as DS, 1030 cases were confirmed by cytogenetic analysis to be DS. Most of these cases (98.43 %) were diagnosed postnatally and only 1.56 % were detected prenatally mainly through amniocentesis and rarely products of conception (0.01 %). Their ages ranged from one hour to 30 years with mean of 351 days. Males represented 54.13 % while females represented 45.87 % of the studied group. Mean maternal age at conception was 31.8 years for cases with non- disjunction and 24.5 years for cases with translocation. All mothers of cases of translocation DS were under 35 years, in contrast to mothers of non- disjunction cases in which 41.48 % were above 35. Paternal age ranged from 19 to 62 years with mean of 36.5 years in non-disjunction cases and from 24-35 years in translocation cases with mean of 30.6 years. Consanguineous marriage was present in 12 % of cases. Positive family history was present in 6 % of cases. Most of cases were the first or the second in order of birth, and the most common cause of referral was dysmorphic features in live births and advanced maternal age in prenatally referred cases. Karyotype revealed that 93.98 % of cases had non-disjunction, while 3.5 % of cases had translocation and 1.84 % had mosaicism. Non- classical karyotype was present in 7 cases (0.68 %). Most of the cases of translocation with (21; 21), which was present in 51.35 % of cases, followed by t (14; 21), which was present in 40.5 % of cases, t (13; 21) in 5.4 %, and t (15; 21) in 2.7 % of cases of translocation. We concluded that, in Egypt 1.6 million births / year and estimated risk of 2285 DS births annually, the concept of preventive genetics should be reinforced with a national policy targeting both health professionals and general publics to offer prenatal genetic screening for all pregnant ladies and prenatal diagnosis for screen positive cases. This needs an integrated system including proper integrated diagnostic facilities, trained personnel and professional staff.
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