The palm lines can be divided into three main zones: the greater fisheye, the lesser fisheye and the interphalangeal zone. The major fisheye is located below the thumb. The Minor Interflexor is located on the lower part of the little finger side of the palm. At the base of each of the second to fifth fingers, there is a trigeminal point, labeled a, b, c, and d. In the lower part of the palm, normally at the base of the greater and lesser pisiforms, near the center of the palm base, there is a trigeminal point called trigeminal t. The line from t to a and d makes an angle, called the atd angle. Palmar atd angle greater than 45deg; is a chromosomal abnormality caused by mental retardation congenital stupidity (21 III syndrome, Down syndrome) special appearance. The symptom is present in approximately 40% of patients. Mental retardation (mentalretardation) is a syndrome in which an individual’s intellectual functioning is significantly lower than that of his or her peers due to mental retardation, impaired or impaired intellectual development, accompanied by difficulties in social adjustment, as the main feature before developmental maturity (usually before the age of 18 years). The atd angle of a normal person is usually indicated by “t”, and the atd angle of a normal person in China is about 41° on average. However, some patients with certain genetic diseases have changes in the position of the trigeminal t-site on the hand resident, thus making the atd angle abnormal. Abnormal atd angle with “t′” and “t″, 46 ° < t′ < 63 ° < t″. For example, the average at′d angle in patients with congenital stupidity is about 70°. Trigonometric t′ occurs in 2% of normal individuals and 82% of congenital stupidity, and trigonometric t″ occurs in 3% of normal individuals, compared with 25% in trisomy 18, 81% in trisomy 13, and 80% in 5P- patients.