Foot with partial syndactyly<unk>  fusion of two toes<unk>  is generally diagnosed based on symptoms, the findings on examination, and the results of an electrocardiogram. Clinical diagnostic criteria have been proposed which suggest that a diagnosis can be made if two of the following four criteria are met: (1) periodic paralysis; (2) ventricular arrhythmias (frequent ventricular ectopic beats or ventricular tachycardia), a prolonged QT interval when corrected for rate, and/or a prominent U wave; (3) at least two of the following dysmorphic features: low-set ears, wide-set eyes, a small mandible, fifth-digit clinodactyly, and syndactyly; and (4) a family member with confirmed<unk> . Genetic testing can be used to identify the specific mutation in an affected person, which if found can assist with screening family members. Other investigations that may be helpful in making a diagnosis include ambulatory ECG monitoring to assess for arrhythmias, measurement of blood potassium levels at baseline and during periods of weakness, and measurement of thyroid function. Differential diagnosis The differential diagnosis for a prolonged QT interval includes other forms of long QT syndrome such as Romano–Ward syndrome in which only the electrical activity of the heart is affected without involving any other organs; Jervell and Lange-Nielsen syndrome in which a prolonged QT interval is combined with congenital deafness; and Timothy syndrome in which a prolonged QT interval is combined with abnormalities in the structure of the heart, in addition to autism-spectrum disorder. The frequent ventricular ectopy and bidirectional ventricular tachycardia seen in<unk>  can also occur in catecholaminergic polymorphic ventricular tachycardia. The intermittent weakness seen in<unk>  also occurs in other forms of periodic paralysis<unk>  hypokalaemic periodic paralysis, hyperkalaemic periodic paralysis, and paramyotonia congenita.
Andersen–Tawil syndrome
Jervell and Lange-Nielsen syndrome
Dennie–Marfan syndrome
Romano–Ward syndrome
Timothy syndrome
Marfan syndrome
Catecholaminergic polymorphic ventricular tachycardia
CAMFAK syndrome