rickets is still a common health problem and is considered to be a challenge even in developed countries .
epidemiological data are not available in many countries , etiology is sometimes difficult to establish and vitamin d supplementation and rickets treatment have been debated for a long time .
a child aged 10 months old was admitted in pediatric emergency department with focal seizures with secondary generalization .
the child has , delay in motor developmental mile stones and hypotonia and poor gain in height .
biochemical and radiologic signs were suggestive for rickets . biochemical profile showing low serum calcium-6.1 mg / dl ( 9.2 - 11 mg / dl ) , low phosphorus-3.9 mg / dl ( 3.4 - 6.2 mg / dl ) , elevated alkaline phosphatase-4116 u / l ( < 269
u / l ) parathyroid hormone was 233.6 pg / ml ( 15 - 65 pg / ml ) 25-oh vitamin d was 40 ng / dl .
radiographic images of the wrist showed fraying and cupping of the distal radius and ulna , as well as bone demineralization ; the metaphyses are widened , irregular and cupped .
physical examination , biochemical data ( hypocalcemia , mild hypo - phosphatemia , high serum concentration of alkaline phosphatase ) and rachitic changes on x - ray , were compatible with the diagnosis of rickets . the child was started on sodium valproate 20 mg / kg / day , calcium 500 mg / day and vitamin d 6 lakh iu following which there was no improvement in the serum calcium level and there was recurrence of seizures .
then endocrinologist opinion sought following which the child was initiated on 0.5 g / day of active vitamin d (  cacidiol ) along with 1000 mg of calcium .
there was no seizure recurrence in the last 15 months and serum calcium normalized . in view of response to 1  calciferol
1,25 oh vitamin d and enzyme studies were not done in view of financial constraints and lack of availability .
a total of 10 different allelic variants of vddr have been identified , exhibiting little or no clinical differences .
prominent clinical manifestations of vddr - i include growth failure , short stature , skeletal abnormalities , genu valgum , rachitic rosary , open fontanels , pathologic fractures , muscle weakness and convulsions .
radiologic findings usually include fractures , generalized osteopenia , growth failure and arched or curved legs .
the most common laboratory findings include hypocalcemia , hypophosphatemia , elevated parathormone levels and high alkaline phosphatase . moreover , the serum levels of 25(oh ) vitamin d are normal or raised while the levels of 1,25(oh ) vitamin d are low or undetectable .
vitamin d is intimately involved in a wide variety of biologic processes , including calcium homeostasis , bone formation and cellular differentiation . in order to exert its effects ,
vitamin d must be activated by a metabolic pathway that requires the enzymatic activity of 25-hydroxylase and 1--hydroxylase .
the gene for vddri has been recently mapped to the long arm of chromosome 12 , region one bands 2 - 4 ( 12q12-q14 ) , representing the location of the 1--hydroxylase gene .
hence , it has been suggested that the disease should be referred to as 1--hydroxylase deficiency .
stong clinical suspicion is required for the clinical diagnosis of vddr and therapeutic challenge with 1  calciferol will prove the diagnosis .
 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)2d ) by the enzyme 1--hydroxylase . 
 patients with vddr - i have mutations of chromosome 12 that affect the gene for the enzyme 1--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 . 
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