The histocompatibility antigens are thought to be the principal genetic factor in disease susceptibility and expression (Bach & van Rood, 1976). This antigen system has been studied in various autoimmune disorders and high incidence of certain HLA antigens has been observed in many diseases. Recently, Goebal et al (1977), while screening 20 patients with ITP, found a high incidence of HLA-B8 and HLA-B12 either alone (70% and 45% respectively) or in combination (40%) as compared to controls which included patients with drug-induced thrombocytopenic purpura and healthy volunteers.We subjected our 20 patients with ITP to HLA phenotype studies. The criteria for the diagnosis of ITP included: (a) a platelet count of less than 100 x 109/l; (b) megakaryocytic hyperplasia with poor platelet production in the bone marrow; and (c) exclusion of any systemic disease, other haematological disorder and antecedent history of intake of drugs o r toxins related to this disorder. Antiplatelet antibodies were present in 12 out of 20 cases (60%) as tested by the platelet factor 3 release test (Karpatkin & Siskind, 1969).HLA profiles were assayed by the two-stage microlymphocytoxity test (Mittal et al, 1968). Well-defined antisera against 23 specificities were used to identify the antigens. Three or four antisera were used against each specificity. Sixty controls included healthy members of our staff and unrelated voluntary donors for patients waiting for renal transplantation. All the patients and controls were from North India and represented the same ethnic group of population. All but three of the patients had not received steroid therapy for more than 6 weeks at the time of HLA phenotyping. One of these patients had been on 20-30 mg of prednisolone per day for 2 months when his HLA typing was carried out. The two other patients had been taking 5-10 mg of prednisolone intermittently for about 2 years when their HLA phenotyping was carried out; one of them had undergone therapeutic splenectomy.HLA-B8 was present in 15% (three patients) as compared to 13.3% in the control. HLA-B12 was observed in 10% (two patients) as compared to 20% in the control population. Combination of HLA-B8 and B12 was not observed in any patient. Statistical analysis using Yates chi-square test did not show any significant association of HLA-B8, B12 or any other HLA antigen with ITP as compared to controls. The present data therefore do not reveal any association between the HLA antigens and ITP in this ethnic group.

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The prevalence of alpha-thalassemia in this cohort of Saudi population was 39.99%. Hb H disease appeared as common as SCD. Sickle cell gene was seen in 23.4% of neonatal samples. alpha-Thalassemia gene significantly reduces MCH, MCV, RDW-SD, Hct, Hb, and increases RBC count in both normal or sickle cell trait neonates. Generally, the variation of red cell parameters is directly proportional to the amount of Hb Bart's in the cord blood. Sickle cell gene in itself produces low MCV, RDW-SD and MCH in cord blood. Further, normal reference values for red cell parameters of cord blood are established.

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