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A tuft of hair above the bottom when present since birth usually indicates an underlying spinal cord
anomalies or other neural tube defects or sometimes kidney
abnormalities .However only the excessive growth of hair without an associated defect may be due to an underlying hormonal
or metabolic problem.Since she is asymptomatic it is unlikely that any major congenital anomalies are present but nevertheless it does warrant an evaluation.
So please consult a pediatrician
for a thorough examination & investigation of your granddaughter to rule out any of the above mentioned problems.
Wishing her good health,