Recent studies suggest that sleeping too much or sleeping too little could be genetically linked. Abnormal sleeping patterns are connected to the regulation of thyroid hormone levels, specifically the DNA region located close to the PAX8 gene. Excessive sleepers are those who sleep more than 10 hours a day, and this condition is called hypothyroidism which occurs when the thyroid glands do not produce enough thyroid hormones. Hyperthyroidism is when too many thyroid hormones are produces which results in insomnia, and those affected sleep less than 6 hours a day.
There is another sleeping pattern where people can function normally with only 4-6 hours of sleeping. This sleep pattern is a result of a mutation in the DEC2 gene, and typically expressed as falling asleep between 11pm and midnight, and waking up as early as 4 pm. This mutation results in alertness decreasing late at night allowing individuals to fall asleep faster, and waking you up alert and ready in the early morning. This mutation is rare, but different sleep patterns are controlled by different genes.