الفهرس 
TitleOnly 14 pages are availabe for public view
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Abstract
Prader-Willi syndrome (PWS) is a complex disorder with a heterogeneous genetic base. Diagnosis may be difficult to establish on clinical background as many features are subtle or non specific and other change with age. Misdiagnosis still occurs. Under diagnosis in younger children and over diagnosis in obese retarded adolescents and adults are both common. Unfortunately, most PWS patients are diagnosed only after obesity is installed.
The present study aimed to reach a proper diagnosis of PWS through a sensible strategy of investigations on the cytogenetics level, molecular cytogenetics level using FISH technique and molecular level using DNA methylation tests for early diagnosis and proper counseling and management.
This study was conducted on 23 patients who were clinically suspected to have Prader-Willi syndrome. The revised criteria proposed by Gunay-Aygun on 2001 were put into consideration.
All patients were subjected to detailed clinical studies; chromosome analysis was done as a routine part of evaluation of these patients in order to rule out other abnormalities, and to detect rare instances of translocations or other rearrangements. FISH was carried out using commercially available probes (Oncor & Vysis), the technique was followed according to the manifacturers’ instructions. Methylation analysis using combined methylation sensitive restriction enzymes and PCR was done. M-PCR was applied as an alternative technique to avoid encountered problems rendering inconclusive results in 4 patients & to confirm the given results in other 4 cases.
-The results of the present study were:
• Sample included 13 males and 10 females with a male to female ratio 1.3:1, with a mean age of 7.23 years.
• Positive consanguinity is present in 9 cases (43.5%).
• Family history of related condition was present in 9 cases. There was no family history of similar or related conditions in the rest of our cases.
-Results of clinical examination were:
• Small for gestational age was present in 4 (17.4%) cases. Average birth weight for gestational age was present in 12 (52.2%) patients and prematurity in one case. History of large for gestational age was present in 4 (17.4%) cases. There were no reliable data given by parents for the rest of cases.
• Infantile hypotonia with poor suck was present in eleven cases (52.4%) and was absent in the rest of our patients, 2 cases were not informative.
• Typical facial features of PWS in the form of narrow bifrontal diameter, almond shaped eyes, and thin upper lip with downturned corners of mouth (carp mouth) were observed in 9 of our cases (39%). Almond shaped eyes were the only feature presenting in the rest 61.0% of patients (14 patients). Coarse facies, in addition to other facial features, was present in 2 cases.
• The least common finding was depigmentation compared to the familial back ground was observed in 2 patients (8.7%). Hypopigmentation involved skin, hair and iris, no fundus hypopigmentation was present.
• Obesity was the most outstanding complaint and cause of referral in our study group. Nineteen out of 23 (82.6%) presented with body weight above 3.0 SD.Their age range was 9-36 months. Four patients less than 1 year didn’t manifest obesity yet.
• Stature was on the mean in 17 cases (74%). One patient was on +2.2 SD Two patients were short within -2.0 SD to -2.5 SD for further height evaluation. Three patients were short below – 2.5 SD.
• Among our 23 patients, only 9 cases (39%) had Small hands and feet with fusiform fingers. Hands and feet size correlated with stature in 4 cases, but not in the other 5 in whom the height was on the mean.
• Hypogenitalism was present in all but 3 cases (87%).
• IQ evaluation conducted on our cases showed: 5 cases within the normal range of mentality IQ ≥ 79. Mental subnormality was present in 14 cases (78.3%) in the form of: border line mental retardation in one case with IQ 70-79, mild MR with an IQ score 50-69 in 7 cases, moderate MR with IQ score 35-49 in 4, to severe MR with IQ score 20-35 in 2 cases. IQ was not available in 4 cases.
-Results of cytogenetic and FISH studies were:
• Out of 23 patients subjected to cytogenetic study of metaphase spreads, 8 cases showed abnormal karyotype analysis in the form of: deletion of 15q 11-13 in all studied metaphases in 2 cases, 50 % deletion of the 15q11-13 region in 3 cases, and 25% deletion in one case. Deletion of the 15q11-13 region was suspicious in 2 cases. FISH confirmed the deletion in all studied metaphases in 5 cases, mosaicism in one case; detected deletion in 4 cases, and excluded deletion in 13 cases.
-Results of Molecular studies:
• Molecular studies were carried on 7 cases showing no deletion on FISH studies and one case with a deletion as a positive control. The 1088bp band SNRPN product was absent following the McrBC digestion in 2 cases, while present in other 2 cases. An abnormally unexplained positioned band was detected in the remaining 4 cases. Using MSP analysis. Both maternal and paternal products of the same intensity were seen at 313bp and 221bp lengths respectively in 6 cases signifying a normal result regarding PWS, while the paternal product was absent in 1 case which is diagnostic to PWS.
-Among the 23 cases of the study group, 11 cases were found to be PWS: 10 of the deletion subtype of PWS confirmed by FISH and 1 case of the non deletion subtype confirmed by molecular studies, 6 cases were excluded from being PWS by molecular studies and 6 cases PWS was not confirmed due to lack of DNA samples (patients refused to complete the test).
-Below normal IQ showed a significant difference between the positive cases of PWS (100%), the negative (66.7%) and the non confirmed ones (50%) (P<0.05). No significant differences were found between the positive, negative and the non confirmed groups regarding the rest of the clinical data.
Conclusion:
-Genetic analysis must be carried out in children with infantile hypotonia of unknown cause, poor sucking and some facial features of PWS (almond eyes and narrow bifrontal diameter, and hypopigmentation), small hands and feet and hypogonadism. This can allow the early diagnosis and avoid invasive exams necessary for neuromuscular disorder diagnosis.
-FISH is very effective in confirming or ruling out deletion of 15q11-13 detected on cytogenetic analysis.
- M-PCR is very accurate and cost efficient for the detection of PWS of any subtype i.e. deletion, UPD or IC defects.
-Cytogenetic analysis is not reliable for the detection of PWS deletions and should only be carried out as a routine to rule out any other chromosomal aberrations.