This is the most direct statement on the ADA and left-handedness I have been able to find.
The actual implementing regulations and the statutory language are not so clear. I have not found any case in which a claim was made under the ADA which cited left-handedness as a disability udner the ADA, either the original act or as amended.
(a) (1) Disability means, with respect to an individual:
(a) (1) (i) A physical or mental impairment that substantially limits one or more of the major life activities of such individual;
(a) (1) (ii) A record of such an impairment; or
(a) (1) (iii) Being regarded as having such an impairment as described in paragraph (f) of this section.
(a)(2) Rules of construction.
(a)(2) (i) The definition of “disability” shall be construed broadly in favor of expansive coverage, to the maximum extent permitted by the terms of the ADA.
(b)(1) Physical or mental impairment means:
(b)(1)(i) Any physiological disorder or condition, cosmetic disfigurement, or anatomical loss affecting one or more body systems, such as: neurological, musculoskeletal, special sense organs, respiratory (including speech organs), cardiovascular, reproductive, digestive, genitourinary, immune, circulatory, hemic, lymphatic, skin, and endocrine; or
(b)(1)(ii) Any mental or psychological disorder such as intellectual disability, organic brain syndrome, emotional or mental illness, and specific learning disability.
(b)(2) Physical or mental impairment includes, but is not limited to, contagious and noncontagious diseases and conditions such as the following: orthopedic, visual, speech and hearing impairments, cerebral palsy, epilepsy, muscular dystrophy, multiple sclerosis, cancer, heart disease, diabetes, intellectual disability, emotional illness, dyslexia and other specific learning disabilities, Attention Deficit Hyperactivity Disorder, Human Immunodeficiency Virus infection (whether symptomatic or asymptomatic), tuberculosis, drug addiction, and alcoholism.
(b)(3) Physical or mental impairment does not include homosexuality or bisexuality.
(c)(1) Major life activities include, but are not limited to:
(c)(1)(i) Caring for oneself, performing manual tasks, seeing, hearing, eating, sleeping, walking, standing, sitting, reaching, lifting, bending, speaking, breathing, learning, reading, concentrating, thinking, writing, communicating, interacting with others, and working; and
(c)(1)(ii) The operation of a major bodily function, such as the functions of the immune system, special sense organs and skin, normal cell growth, and digestive, genitourinary, bowel, bladder, neurological, brain, respiratory, circulatory, cardiovascular, endocrine, hemic, lymphatic, musculoskeletal, and reproductive systems. The operation of a major bodily function includes the operation of an individual organ within a body system.
(c)(2) Rules of construction.
(c)(2)(i) In determining whether an impairment substantially limits a major life activity, the term major shall not be interpreted strictly to create a demanding standard.
(c)(2)(ii) Whether an activity is a major life activity is not determined by reference to whether it is of central importance to daily life.
(d) Substantially limits.
(d)(1) Rules of construction. The following rules of construction apply when determining whether an impairment substantially limits an individual in a major life activity.
(d)(1)(i) The term “substantially limits” shall be construed broadly in favor of expansive coverage, to the maximum extent permitted by the terms of the ADA. “Substantially limits” is not meant to be a demanding standard.
(d)(1)(ii) The primary object of attention in cases brought under title III of the ADA should be whether public accommodations have complied with their obligations and whether discrimination has occurred, not the extent to which an individual’s impairment substantially limits a major life activity. Accordingly, the threshold issue of whether an impairment substantially limits a major life activity should not demand extensive analysis.
(d)(1)(iii) An impairment that substantially limits one major life activity does not need to limit other major life activities in order to be considered a substantially limiting impairment.
(d)(1)(iv) An impairment that is episodic or in remission is a disability if it would substantially limit a major life activity when active.
(d)(1)(v) An impairment is a disability within the meaning of this part if it substantially limits the ability of an individual to perform a major life activity as compared to most people in the general population. An impairment does not need to prevent, or significantly or severely restrict, the individual from performing a major life activity in order to be considered substantially limiting. Nonetheless, not every impairment will constitute a disability within the meaning of this section.
(d)(1)(vi) The determination of whether an impairment substantially limits a major life activity requires an individualized assessment. However, in making this assessment, the term “substantially limits” shall be interpreted and applied to require a degree of functional limitation that is lower than the standard for substantially limits applied prior to the ADA Amendments Act.
(d)(1)(vii) The comparison of an individual’s performance of a major life activity to the performance of the same major life activity by most people in the general population usually will not require scientific, medical, or statistical evidence. Nothing in this paragraph (d)(1) is intended, however, to prohibit or limit the presentation of scientific, medical, or statistical evidence in making such a comparison where appropriate.
(d)(3) Condition, manner, or duration.
(d)(3)(i) At all times taking into account the principles set forth in the rules of construction, in determining whether an individual is substantially limited in a major life activity, it may be useful in appropriate cases to consider, as compared to most people in the general population, the conditions under which the individual performs the major life activity; the manner in which the individual performs the major life activity; or the duration of time it takes the individual to perform the major life activity, or for which the individual can perform the major life activity.
(d)(3)(ii) Consideration of facts such as condition, manner, or duration may include, among other things, consideration of the difficulty, effort or time required to perform a major life activity; pain experienced when performing a major life activity; the length of time a major life activity can be performed; or the way an impairment affects the operation of a major bodily function. In addition, the non-ameliorative effects of mitigating measures, such as negative side effects of medication or burdens associated with following a particular treatment regimen, may be considered when determining whether an individual’s impairment substantially limits a major life activity.
(d)(3)(iii) In determining whether an individual has a disability under the “actual disability” or “record of” prongs of the definition of “disability,” the focus is on how a major life activity is substantially limited, and not on what outcomes an individual can achieve.