CSV/XLS to customised nested JSON/TSV in R - r

Question

I have a XLS file in the following format-- XLS input file. The first column is just for explanation of JSON elements. I want to convert the column headers into main elements and then the next 4 rows into nested JSON elements. The desired JSON file will look like this-- JSON output file. I have tried string substitution in python which makes it easier but is there any way to do this in R?
XLS file -- XLS input file Excel link
Desired JSON output--
{
"MRI ID": {
"Description": "MRI ID"
},
"Participant ID": {
"Description": "Participant ID"
},
"Group": {
"Levels": {
"Case": "",
"Control": "",
"Cohort": ""
}
},
"Gender": {
"Levels": {
"Male": "",
"Female": "",
"Other": ""
}
},
"Age": {
"Units": "Years"
},
"Vocab Raw Score WASI": {
"Description": "Wechsler Abbreviated Scale Intellegence",
"Units": "Raw Score"
},
"Handedness": {
"Levels": {
"Left": "",
"Right": "",
"Ambidextrous": ""
}
},
"Last 60 Days Number of Drinks TLFB": {
"Description": "Alcohol Timeline Followback",
"Units": "Drinks"
},
"Last 60 Days Drinking Days TLFB": {
"Description": "Alcohol Timeline Followback",
"Units": "Days"
},
"Last 60 Days Average Drinks Per Drinking Day TLFB": {
"Description": "Alcohol Timeline Followback",
"Units": "Average Drinks Per Drinking Day"
},
"Last 60 Days Number of Non-Drinking Days TLFB": {
"Description": "Alcohol Timeline Followback",
"Units": "Days"
},
"Last 60 Days Max Number of Drinks TLFB": {
"Description": "Alcohol Timeline Followback",
"Units": "Days"
},
"Last 60 Days Number of Heavy Drinking Days TLFB": {
"Description": "Alcohol Timeline Followback",
"Units": "Days"
},
"Last 60 Days Number of Cigarette Smoking Days TLFB": {
"Description": "Nicotine Timeline Followback",
"Units": "Days"
},
"Last 60 Days Average Number of Cigarettes on Smoking Days TLFB": {
"Description": "Nicotine Timeline Followback",
"Units": "Average Cigarettes"
},
"Last 60 Days Number of Non-Cigarette Smoking Days TLFB": {
"Description": "Nicotine Timeline Followback"
},
"Last 60 Days Max Number of Cigarettes TLFB": {
"Description": "Nicotine Timeline Followback",
"Units": "Cigarettes"
},
"Last 60 Days Number of Marajuana Smoking Days TLFB": {
"Description": "Cannabis Timeline Followback",
"Units": "Days"
},
"Last 60 Days Number of Non-Marajuana Smoking Days TLFB": {
"Description": "Cannabis Timeline Followback",
"Units": "Days"
},
"Matrix Reasoning Raw Score WASI": {
"Description": "Wechsler Abbreviated Scale Intellegence",
"Units": "Raw Score"
}
}