Classical homocystinuria (HCU) is the most common inborn error of metabolism in Qatar, with an incidence of 1:1800, and is caused by the Qatari founder p.R336C mutation in the CBS gene. This study describes the natural history and clinical manifestations of HCU in the Qatari population. A single center study was performed between 2016 and 2017 in 126 Qatari patients, from 82 families. Detailed clinical and biochemical data were collected, and Stanford‐Binet intelligence, quality of life and adherence to treatment assessments were conducted prospectively. Patients were assigned to one of three groups, according to the mode of diagnosis: (a) late diagnosis group (LDG), (b) family screening group (FSG), and (c) newborn screening group (NSG). Of the 126 patients, 69 (55%) were in the LDG, 44 (35%) in the NSG, and 13 (10%) in the FSG. The leading factors for diagnosis in the LDG were ocular manifestations (49%), neurological manifestations (45%), thromboembolic events (4%), and hyperactivity and behavioral changes (1%). Both FSG and NSG groups were asymptomatic at time of diagnosis. NSG had significantly higher intelligence quotient, quality of life, and adherence values compared with the LDG. The LDG and FSG had significantly higher methionine levels than the NSG. The LDG also had significantly higher total homocysteine levels than the NSG and FSG. Regression analysis confirmed these results even when adjusting for age at diagnosis, current age, or adherence. These findings increase the understanding of the natural history of HCU and highlight the importance of early diagnosis and treatment. Synopsis A study in 126 Qatari patients with HCU, including biochemical, clinical, and other key assessments, reveals that patients with a late clinical diagnosis have a poorer outcome, hereby highlighting the importance of early diagnosis and treatment.

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A total of 78,428 blood units collected by the Blood Donor Unit, Hamad Medical Corporation, Doha, from the multinational donors of Qatar (28,622 Qatari nationals donors and 49,806 Non-Qatari donors) in the period January 1994 to Dececember 2001 were screened for hepatitis markers. About 10,382 units (13.2%) were discarded because of positivity for one or more hepatitis markers; 769 units (0.9%) were positive for hepatitis-B surface antigen (HBsAg), 8516 units (10.9%) were positive for hepatitis-B core antibodies (HBcAb) and 1097 units (1.39%) were positive for hepatitis C (HCV) antibodies. There was no significant difference between the rate of positivity for HBcAb and HBsAg in indigenous Qataris and Non-Qataris despite a slightly higher rate ofpositivity for HCV antibodies in the Non-Qatari group. An outstanding finding was the significantly high rate of positivity for HCV antibodies in Egyptian donations (11.2%), which accounted for 31.2% of all discards for the Non-Qatari group. As the Blood Donor Unit at HMC is the only blood collection center in Qatar it is assumed that the results could be representative of the country as a whole.