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There are two types of vitamin D dependent rickets (VDDR) that cause rickets in children. VDDR type 1 (VDDR-I) is caused by an inborn error of vitamin D metabolism, which interferes with renal conversion of calcidiol (25OHD) to calcitriol (1,25(OH)2 D) by the enzyme 1-α-hydroxylase. Patients with VDDR-I have mutations of chromosome 12 that affect the gene for the enzyme 1-α-hydroxylase, resulting in decreased levels of 1,25(OH) vitamin D. Clinical features include growth failure, hypotonia, weakness, rachitic rosary, convulsions, tetany, open fontanels and pathologic fractures. We report a case of VDDR-I in 14-month-old male child. Establishing an early diagnosis of these genetic forms of rickets is challenging, especially in developing countries where nutritional rickets is the most common variety of the disease where genetic diagnosis is not always possible because of financial constraints. A prompt diagnosis is necessary to initiate adequate treatment, resolve biochemical features and prevent complications, such as severe deformities that may require surgical intervention. [ABSTRACT FROM AUTHOR]